Resilience of Air Traffic Management system [302113]
Air Navigation
Resilience of Air Traffic Management system
BEng Final Project
Author: Vasile Alexandra
Supervisor: Cristian Constantinescu
Session: July 2017
Anti-Plagiarism Declaration
I [anonimizat]: [anonimizat], [anonimizat], individual work. All the external sources of information used were quoted and included in the References. [anonimizat], and tables taken from external sources include a reference to the source.
Date: _________ Signature: __________________________
Terminology and Acronyms
Abstract
Table of contents
List of figures
Figure 1.1
Figure 1.2
Figure 2.1
Figure 3.1
Figure 4.1
List of tables
Table 1.1
Table 1.2
Table 2
Table 3
Table 4
Chapter 1. Introduction
This dissertation is a research study on resilience in Air Traffic Management (ATM) [anonimizat] a long term air traffic growth [1]. This paper analyse several disruptions that may appear in the air transport system and their impact on its performance. [anonimizat].
There are a number of elements that are strongly interacting and collaborating in order to ensure a safe air transport system. Thus a [anonimizat]. [anonimizat], without any delays or negative consequences regardless the difficulties encountered during the flight from departure until arrival.
[anonimizat] a system which can be defined by the ability of the system to quickly recover regardless the disruptions and problems there may appear. [anonimizat], and in the same time assure a smooth air traffic flow and the airspace users safety.
What it can be called a ‘disturbance’ [anonimizat], human errors that triggers a ‘perturbation’, a [anonimizat].
The following chapters will attempt to define and measure the resilience of the system by quantifying the impact of disturbances in time over the air transport system. [anonimizat]. A modified trajectory resulted from a disruption will be calculated.
[anonimizat], as follows [3]:
[anonimizat] a system needs to be defined. Thereby the system will be associated with a structure composed of several objects with specific attributes.
By the current state of a system we evaluate the present values of the system performance indicators.
Reference state of a system is the specified set of its performance indicators values. A reference state (at the moment of its specification) relative to the current state of the system can be either an actual reference state, when the current values of the performance indicators are in the specified set of performance indicators values; or a potential reference state, when at least one of the current values of the performance indicators is not in the specified set of performance indicators values.
Stress is a reaction of a system, the state of a system caused by a disturbance which differs from the reference state and is characterized by deviation from this reference condition. If the system presents no change in the current state it means there is a survival stress, while the lethal stress means that the system has to be modified.
Through a disturbance one may understand a phenomenon, factor, or process that will influence the system either internal or external by producing a so call ‘perturbation’ with a dependency on the initial reference state. [pdf 1.3*]
The concept of ‘perturbation’ mentioned before represents the reaction of the system when the current state performance indicators changes, in other words an effect/consequence. [pdf 1.3*]
Robustness – the ability of a system to experience no stress since a disturbance had occurred, i.e. the system is robust against the disturbance over the considered time horizon; is relative to the specified reference state of the system and to a particular disturbance [pdf1.3]. In other words after a disturbance the system maintains its state within the boundaries of state reference.
Air Navigation Service Providers (ANSPs) are organizations providing Air Navigation Services and are responsible for accommodating traffic growth by providing capacity at agreed air traffic flow management delay levels to meet customer requirements and the most cost-effective air transportation service. [ECTL08]
Chapter 2. Resilience of a system. Resilience of ATM system
Resilience as a general notion
For a better understanding of what resilience refers to, a short history of the notion will be presented. The term ‘resilience’ is a widely used concept in many different domains, that over the years become extensively studied with various interpretations. Although it has his origins in English back in history in the 16th – 17th century, it was first introduced by R.M. Hoffman in the field of mechanics and material testing in 1948 and one decade later Holling implemented the term in ecology [site, pdf 1.1*]. Its etymology is unclear, being specified two terms from the Latin: ‘resilientia’ translating into ‘fact of avoiding’ and ‘resiliens’ with its translation ‘leap back’ (Oxford English Dictionary, 2012).
Hoffman applied the concept of resilience for substances and materials, the term describing the capacity to return to its original state after the applied force/tension have ceased. He observed, analysed and classified the substances based on their reactions to an external stress in an unit time. In this way, substances could be included in different categories as follows:
The first one is high resilience that has a low response and high recovery;
The second one is medium resilience which could be split in another 2 sections: one with both response and recovery high, while the second sections present the same essential parameters as a low ones.
The third one, consider low resilience in terms of high response and low recovery. [site, pdf 1.1*]
This simple classification gives a better perspective on the returning to normal ability of a system. Further discussions on resilience metrics will be held in a next chapter.
Strunz claimed in 2012, that ‘resilience’ as a concept in distinctive domains is ‘polysemous’ [site, pdf 1.1*] suggesting the fact that even if the variously used concept interpretations might be similar, they are actually not the same. Being examined in different social and social-specialized framework contexts, the term acquired some comparable form definitions that shall be mentioned, as follows.
Engineering resilience as noted by Hoffman, defines resilience as the time required for a system or as the ability of a system or as the capability of a substance to return to an equilibrium or steady-state or original state, following a disturbance or sometime later after the removal of the disturbance factor [site, pdf 1.3]. Engineering resilience is based on two important characteristics: resistance and recovery. Through a resistant system it can be understood that there will be no significantly changes in the system, while recovery indicates how fast a system can return to its current state.
Hollnagel expressed resilience engineering (2006) as a concept through which human and organizational aspects can be monitored in terms of reactions to pressure [site, pdf1.3*].
Stepping on to another domain, ecological resilience is defined in the ……. as “the ability or as the capacity of a system to absorb a disturbance, whilst essentially retaining the same function, structure, identity and feedbacks” [site, pdf 1.3]. In contrast to engineering resilience, this means the system does not return to its initial point of equilibrium after a disturbance occurs. Instead it maintain its initial parameters.
In an ecological context, one can explained these notions through a box within it is found a dot that represents the configuration of a system. As a result of disruptions, the resistance of the dot can be measured in terms of returning speed to its initial location, also known as recovery. Resilience instead, with respect to the dot means that the dot can move around the box as long as it respects its limit and remain inside, in other words maintain a similar stable state. [site, pdf 1.1*]
Figure – The current ‘state’ of a system may be defined by key characteristics relating to structure and process (the ‘box’) [site, pdf 1.1]
Resilience applied on ATM system
The air transportation system is permanently disturbed by various disruptions that take place in different locations, airport, at different time. These can raise a series of events that will affect the entire system. Such events may cause small perturbations on passengers discomfort (rerouted flight, rescheduled passengers), while others (mid-air collision, volcanic ash, hazardous weather) have a significant impact on flight operations, air travellers and system performance. All these accidents and incidents proves it is necessary for ‘resilience’ concept to exist. Although all these events are unfortunate, they can be a source of learning where things went wrong for further improvements.
Figure – Air transportation resilience pyramid [ site, pdf 1.1]
A proper functioning system of our daily flights is maintain throughout the interoperability of the socio-technical Air Transport system and a wide information system that aims to attain a high level of performance, safety and flight efficiency. There are a number of factors taken into account when achieving the required demands and fulfil at the same time the standards of European Organisation for the Safety of Air Navigation (EUROCONTROL). These implies cost effectiveness, environmental impact, time based operations and the flexibility of the system.
In this paper, resilience and its importance in the Air Traffic Management system (ATM) will be presented in relation with disturbances and perturbations. Therefore, some basic ideas on ATM system shall be expressed.
Air Traffic Management system is a framework that encompass all the necessary processes and control systems that sustain a safe and orderly air traffic flow. This is done by….. the air and ground based communications, navigation and surveillance services. Apart from ensuring flight guidance from departure until arrival, air traffic management system must offer the same airspace performance over time regardless the changing environment. For this purpose a collaborative integration of human resources, procedures and technical services is required.
ATM is divided in three main departments, that carry out different activities: Aeronautical Information Services (AIS), Air Traffic Control (ATC) and Air Traffic Flow Management (ATFM). Aeronautical Information Services provides all the necessary information to ensure a smooth and efficient air traffic flow, while Air Traffic Control includes area control centre, approach and tower control service and provides minimum separation between aircrafts en-route, as well as in terminal areas around the airports in order to prevent air/ground collision. Air Traffic Flow Management instead, is the department within ATM system that handles the air traffic capacity, that is to say the department that ensures the number of flight per hour over a certain airspace sector, will not exceed the number of flights air traffic controllers can safely cope with. On overview over the flights at a given time can be held through the flight plans completed by the pilots before departures and analysed by the ATFM Centre. However, due to hazardous weather or other issues there may exist many variations in the air traffic flow that could outcome in several disruptions in the airspace capacity. Thus involving more attention from the operators. [wiki *+ eurocontrol site*]
Resilience in ATM domain becomes a subject of more and more interest in recent times. That is because once with a fast growth in air travel demands (flights), the system ability to react to a changing environment has been minimized.
EUROCONTROL described resilience as ‘the intrinsic ability of a system to adjust its functioning prior to, during, or following changes and disturbances, so that it can sustain required operations under both expected and unexpected conditions’ [2].
In other words, resilience in ATM system represents a fundamental property of the system to recover its normal function in a short period of time after being subjected to certain changes or disturbances. The uncertainty of latter (weather, technical issues, human actions) makes difficult the prediction of the impact these will have over the flight operations and ATM system. Thus, a well-coordinated operations and human operators actions, along with the procedures and regulations ensures the system flexibility in normal and abnormal conditions [site, pdf 1.2*].
The adaptability, recoverability and the absorptive capacity are the most important characteristics when defining the resilience and in the same time, essential/vital for sustaining such a complex and important system as the ATM.
The adaptability of a system is expressed in the capability to avoid a change in state regardless the type of disturbance or the time interval under which the system was subjected. An adaptive cycle requires certain internal or external actions to establish its initial stability after a collapse due to expected or unexpected events. In terms of recoverability, the amount/interval of time a system needs to regain its equilibrium shall be reduced to a minimum for achieving a high performance.
From the Journal of Air Transport Management it can be identified a key parameter in the definition of resilience: ‘ability to absorb change and disturbance and still maintain the same relationships between populations or state variables’ [4] that is its absorptive capacity.
For a better understanding of why resilience shall be incorporate in the ATM system, it is necessary to throw a look through the relationship between safety management and engineering resilience.
The safety of a system cannot rely only on the possibility to predict probable failures. For an efficient safety management system there must exist permanently improvements done in order to overcome the unexpected disturbances such as the break-down or the system malfunctioning [2*]. Accident analysis and risk assessment are methods that came in response to problems following certain disruptions (with a significant or insignificant impact). These can be used as a lesson for the entire system of how to handle future similar situations.
As mentioned in an EUROCONTROL document ‘procedures and instructions are always incomplete, except for extremely simple situations’ [2]. To compensate for this lack of organization of the infrastructure and in order to be able respond to the current demands of current air traffic flow, we need to be able to represent the variability of the system.
Resilience Engineering establish the path for normal conditions by identifying potential risks, analysing the things that could go wrong and preventing them through the variability of the system [2*]. Such, a model of variability can be described along with its impact on performance, positively or negatively.
Figure – The set of possible outcomes [2]
In Figure … it can be seen the relation between the outcomes and predictability, having as a quantitative measure, predictability from very low to high and from negative to positive for outcomes; where crossing positive and very high .. means that things go right, while negative and very low means a disaster [2*].
Due to a continuously increase in traffic, the ATM system must cope with demand and future technical improvements without neglecting the financial pressures as well as the environment and safety aspect. The main concern remains in these areas since, because the main objective for the air transport system is to remain profitable, reliable and safe even with the traffic growth and ATM infrastructure changes. Delays and rerouting are the main drawbacks that deteriorate the ATM system performance, especially from an economical point of view.
System performance framework
It is necessary to illustrate a performance framework by means of performance indicators for emphasizing the related outcomes on the complex ATM system. This type of specialized metric targets the performance monitoring and analysis. Having as reference the key performance indicators (KPIs) and areas (KPAs) defined by ICAO in the Manual on the global performance of the Air Navigation System, one can evaluate the state of performance and the validity over a period of time. The following factors comply with High Level goals of SES (Single European Sky) and SESAR (Single European Sky ATM Research) [site, pdf 2*] and will serve as means to measure resilience [site, pdf 1.3*].
To begin with, efficiency will be mentioned. This express the operational and economical point of view of daily flights, in terms of time, resources, consumption and materials. With an increased number of airspace users in the last decades because of the short time of travel, the ATM system has to constantly take into account the optimization of flights trajectories.
Another important factor that defines the performance of air transportation system is the cost-effectiveness. The economical point of view cannot be neglected when the interests of ATM system are at stake. The costs of travel ought to dependably be considered in such a way that any of the airspace clients may afford.
For attaining a high level of system performance the notion of capacity has to be considered. This means the air transportation service must fulfil the requested flights and ensure the frequency in a certain air sector regardless the uncertainty data due to disturbances. Thus resilience interpose. The purpose is to response the demands in any conditions, guaranteeing in the same time there will be no unfavourable effects on the environment or flight safety. Since there is a continuously increase in the air traffic flow there shall exist a commensurate capacity increase defined as number of flights per hour in a specific airspace sector.
Sustaining the capacity of air transportation system results in a need of system flexibility. That is to say the ability to constantly modify the aircrafts trajectories and change the take-off and entry times, while keeping a satisfactory level of performance. Flexibility is a defining factor in the profitability of the system through its adaptability to external disruptions.
Performance implies the predictability of the system in such that the airspace clients and ATM specialized organizations must be able to give predictable and trustworthy levels of execution. Having this in mind, a schedule of air transportation system can be developed giving the possibility to know in advance the system state.
Next, the safety factor is presented as being one of the highest priority of the air navigation service providers. ATM must comply all safety standards and apply the required processes and practises. To ensure the passengers safety and keep their reliability in air transport travel, permanently improvements must be made in air traffic management, flight and ground operations and emergencies services. The aims of these measures is to prevent and reduce the number of accidents. Therefore a vigorously airspace overview is recommended, together with an increase in the airspace capacity and efficiency. A collaborative function between technical subsystems must not be forgotten.
Furthermore, ATM system must contribute to the security and safety risk management. That is to say the protection against various threats that may influence flight or ground influences. From human errors or natural catastrophes till purposeful incidents like terrorism acts or information gap, any attempt considered a dangerous situations must be avoided. ATM system has the responsibility to offer necessary assistance for attaining the adequate protection system.
On the other hand, ATM framework ought to take into consideration impact of flight operations over the environment. In consequence, noise, gaseous emissions and other environmental issues cannot be neglected and certain solutions shall be implemented in the global ATM system.
Entire ATM system should rely on common procedures and standards, otherwise said on the global interoperability. This ability to transfer information will facilitate technical and operational activities and will establish an optimum, harmonised system that will sustain air traffic growth.
Another performance indicator is represented by access and equity. Through this a fair and equitable access to all services for air transport operators shall be provided for all airspace users and should be part of any airspace modernization plan.
Finally, to meet the increased demands of airspace users there is a need of permanently involvement of the ATM community in planning, implementation and operation of the system. Thus, several yearly meetings with the participation of aerodrome community and ATM service providers will take part on discussing air navigation system development.
All the indicators presented previously defines a performance framework. They help assessing the current state of ATM system regarding the operational performance with an eye to further improvements. Having as objective the resilience measuring, an analysis over disruptions consequences on Air Traffic Management system performance is required, that incorporates key performance indicators and areas.
Emergent behaviour
Due to the interactions between various human operators, technical systems and procedures, the air transportation socio-technical system exhibits emergent behaviour [site, 1.1]. Emergence is a common property that has to be considered when introducing the newly defined expression of resilience [pdf, 1.3]. It express the behaviour of the system and it can be predicted through several ways such as mathematical analyses or simulation. Of course, there is the possibility of not being able to predict it.
Some examples are propagation through the network of some disturbances, as reactionary delays or the impact on the performance of the system of failures of elements that may seem independent, but which indirectly interact, and lead to important consequences [site, 1.1]. Emergent behaviour can be classified in categories as it will be further presented
Andrew Cook in the book ‘Applying complexity science to air traffic Management’ mentioned four types of emergent behaviours. First type represents a fully prediction of air/ground technical systems behaviour. The second one instead, have in sight pilots and controllers behaviours, their actions and interaction within the system. Type III of emergence is subjected to certain changes in the feedback loop, its turbulent behaviour making it difficult to predict. When hazardous elements cause perturbations in the air transportation system, the submissiveness to the existing regulations may involuntarily worsen the situation. In contrast, the last one express a behaviour that cannot be predicted because it describes the appearance of a new system. [4*]
Resilience importance
Resilience plays an important role in building a new air transport infrastructure system, a more sustainable and elastic one when uncertain changes occur. It seems like predicting the future is a limited option. But instead we can anticipate, monitor and evaluate the unexpected conditions based on learning. System vulnerabilities should be identified at a performance and connection level, for further strategies and appropriate actions. Such, some properties of the resilience will be brought in discussion, essential ones in the process of accommodating the present infrastructure system into a new adaptable one.
There are four interrelated pillars that we need to consider when we want a resilient system. These are anticipation, monitoring, response and learning [HRE12*].
Figure … – The four pillars towards a resilient system
Anticipation is concerning the future and different disruptive scenarios. Knowing the threats, the potential disturbances and the perturbations that may appear, to expect the possible changes means to realize when the system ability to adapt and recover will drop.
Monitoring is another important milestone, to look for irregularities in the system, to gather metrics and supervise them. Like that threats may be prevented before escalate into a big event with significant effects.
The response of the system means how the system react when sudden changes appear and how the system can be modified in order to cope with them. Attention must be paid to the response because this can cause repercussions in the nodes of the network. Taking into account the anticipation pillar, it can be stated that response implies risks due to predicted events that may prove to be accurate or wrong. In the latter situation, money will be wasted on the unnecessary actions. Thus, a balance must exist between these milestones.
Lastly, but not the least important is the learning pillar. Here, the emphasized aspect is what had happened and what could be learned from that breakdowns and mistakes in order to use it for future improvements. By doing that, the stability of the system will be increased.
Chapter 3. Disturbances framework
Uncertainty
In such a complex system as Air Traffic Management system is, uncertainty of flight operations and flight trajectories must be taken into account. Such analysis can provide information on the current and future state of the air traffic flow. Understanding the uncertainty impact over the flights may outcome in several improvements in the air transportation system, based on various conditions models. Further discussions attempt to highlight the sources of uncertainty due to which delays and rerouted flights occurs with negative social-economical effect on ATM system [1 + 4*].
Uncertainty can be related to operational, technical or weather issues. In other words, one can expect various changes of the environment coming from system break-down, equipment failures or human factors, such as flight operators decisions. Also data uncertainty and data unavailability must be mentioned. While the first one refers to a certain level of vulnerability regarding information, the other one express the lack of information because administrative barriers. [4*].
Uncertainty scales
Having in mind the uncertainty data previously mentioned, an uncertainty scale was introduced in order to accomplish a better system management. Thus, 3 scales presented in the next table will be described in few words: the microscale, mesoscale and macroscale [4*] [ACB*].
Table …. – Network scales [A.C. Book] – page 13
The first one, the microscale have in view in particular the individual flights. Here are taken into account statistics delays, delay propagation models and trajectory uncertainty by deliberating initial conditions, wind conditions and aircraft performance.
The second one, the mesoscale is associated to a group of flights and express the interaction between flights and weather systems. It describes the air traffic flow management problems framework [1*] (management procedures, human actions and unexpected weather). This scale can disturb the connectivity of a system as a whole since it is considered to be a transitional order between an element and a group.
The last one, the macroscale corresponds to the entire air transport network. Looking for system oversights, this macroscale implies microscale and mesoscale analyses concerning safety assessments [1+4*]. The system is viewed through the macroscale as a whole, that takes into account the way the information is spread through the network and incorporate the metrics of the entire structure.
Disturbances Statistics related to delays
Disturbance express an event or a factor that produce a perturbation in the system, deteriorating in this manner its normal function. The outcome is loss of ATM performance and inappropriate operations.
Being considered notable events with a significant impact on safety assessments and properly function of the ATM system, flight delays and their disturbances requires statistical database. Central Office for Delay Analysis (CODA) of EUROCONTROL provide such a database with information on the air traffic delays based on the IATA (International Air Transport Association) standardized codes that attributes to each flight delay a cause. These data are considered only for Europe. [EUROCONTROL*]
Relevant information are presented in a CODA Report from 2016 related to the operational data received from the airlines. In the next picture, it can be seen the major causes for delays in 2016 expressed in minutes of delay per flight comparatively with the numbers obtained in the 2015. A slightly increase in airline and weather delays is shown. [9*]
Figure … – Main primary groups of delay causes [EUROCONTROL, CODA, 2017]
Another useful information with respect to the delays causes statistical data, this time expressed in percentages are made public on the Network Operations Portal (NOP) website. There exist a wide range of disturbances that may appear in current or future ATM operations and below are shown some of the most common reasons for them, using the data from the ATFCM Network Situation data.
Table …. – Situation data last updated 06/05/2017, 14:10 [https://www.public.nm.eurocontrol.int/PUBPORTAL/gateway/spec/]
Identified disturbances
A SESAR paper [7] provides detailed disruptions, classified from several points of view such as weather conditions, human resources, interoperability between systems, technical disturbances, based on 525 identified hazards and possible events that may influence the ATM system.
Table … – Hazards and hazard clusters examples [7]
Towards a more comprehensive approach, several groups of disturbances will be interpreted. Starting with disturbances due to technical systems, it can be said that such issues may be related to radar coverage and the existed blind spots, radar malfunction, systems degradation of the aircraft such as the brake system or issues due to the Flight Management System (FMS), for example differences between the ATC and FMS plans.
When talking about human performance, fatigue represents an important factor in the controllers/pilots behaviour due to which certain disruptions may appear. As Hollnagel cited “Actions by human operators can fail to achieve their goal in two different ways: The actions can go as planned, but the plan can be inadequate, or the plan can be satisfactory, but the performance can still be deficient” (Hollnagel, 1993) [8]. Here it can be mentioned as well wrong positions reports and mixed ATC clearances types. With respect to the communication and coordination it can be enumerated several examples like unsuitable phraseology, erroneously reads back, wrong frequency shifts between the controllers, or the usage of a language other than English, the international language for civil aviation. It is well known that one cannot fully rely on computers and this is way human decisions and actions are demanded, to be able to control unexpected situations that took place in air traffic management service [site, 1.2*].
Strikes or staff issues, in other words industrial actions can be another important factor that may generate arrival or departure delays. Depending on the duration of strikes, they have a disruptive effect on air traffic flow and induce dissatisfaction among airspace users because of their rescheduled flights. [site, 2.1*] 15 days prior to the strike, the Network Manager is announced and the information is made public through the NOP. Preparations are taken in the Network Manager Operations Centre and the communication between air transport entities of interest is intensified. [EUROCONTROL, 10*] Also, illness through the airport staff or crew members involve certain problems in the proper evolution of the flight, including the ground handling service (sustained by the SMGCS-Surface Movement Guidance and Control System). [site, 2.1*]
‘Weather is one of the greatest hazards to aviation. Making correct and timely decisions are important to keeping to schedules and maintaining safety’ [6]. The biggest problem related to weather conditions are the wind, the rain, snow and the fog phenomena, these ones being extremely frequent encountered. Based on the METAR (weather information report) data, the meteorological phenomena can be predicted with respect to time and delays. [2.2*] Its information consists of time, temperature, visibility, humidity, pressure values, wind direction and wind speed. They are emitted once an hour or half an hour. [wiki]. Nevertheless, it must not be forgotten the rare events but with a huge impact over the entire airspace traffic such as hurricanes. Hurricane Sandy that occurred in North America in 2012 is one of the events that caused important disturbances even in the European air transportation system [Is ATM resilient*].
A classification of weather conditions can be estimated based on how much its disturbances influence the system. In the next table, number one means significant consequences, while sixteen is minimum critical. As it can be noticed, thunderstorms represents one of the most important hazards in air transportation, after tornados which are very rare. Their combination with rain, snow or hail makes it even worse, extremely unpredictable and dangerous to the safety of air traffic management. These phenomena results in turbulence, low visibility, windy conditions, runway contamination with snow, that overload the air traffic operators work.[site, 3.1*]
Table – …… [site, pdf 3.1]
Not only that all these weather phenomena represents one of the most frequent and important factor for delays, but it also implies weather avoidance. This leads to necessary modified trajectories in order to avoid adverse weather. A trajectory analysis due to delays will be further discussed in a following chapter of this paper. Apart from rerouted flights, there may be flight cancellations when extremely events such as volcanic eruptions mentioned before take place. Such unexpected changes of trajectories and delays conclude in a money loss of air transportation system.
Last, but not least, the unknown flying objects (e.g. balloons, paragliders) or other events such as air shows event though they have a minor impact on the ATM, they are increasing the capacity in the air traffic system in certain sectors.
Nevertheless, the system is vulnerable to major possible events, such as volcanic eruption, terrorists’ assault, nuclear accidents or cyber threat. [EUROCONTROL*] Even though they are very rare all the entities and authorities with respect to aviation should be aware of them and prepare for them, before a big disaster took place. As related to the volcanic ash, a serious event happened in 2010 around one of the largest volcanoes in Iceland, where a small volcano erupted, causing big air travel disruptions for several days [Skybrary*]. The ash cloud, as an outcome of the eruption, diminish the number the flight to more than half (a percentage of 53.6%) during a period of 7 days in April. The situation was supervised and updated by the CFMU, which also had the priority of sharing all the relevant information gathered (e.g. ash cloud anticipated movement reports). [EUROCONTROL, 11*]
Quantification of disturbances
Disturbances may be evaluated and classified by type, duration, frequency and intensity [3*]. Since several examples were previously highlighted, it will be now shown how disturbances can be categorized.
Related to the frequency of disturbances, they can be very rare, rare, occasionally and regular site, 1.2*]. Taking into account an airport with 300,000 flights per year, the probability of disturbance that may arise per flight can be expressed with approximation for each of the mentioned categories. Therefore, very rare means less time 3 times per 10 years such as ATC centre evacuation, radar failure with significant impact on ATCs. Rare class provides a roughly estimation between 3 times per 10 years and 30 times per year for FMS (Flight Management System) errors or wrong use of the runway, while occasionally offers a percentage between 30 times per year and 4 times per day when talking about changes in procedures. Last, but not least, a regular disturbance has a probability of more than 4 time per day site, due to the flight operators high workload (pilots and controllers attention may have several consequences on the proper interaction between them) [1.2+].
Depending on the type, disruptions can be arranged in three classes. A low-level class that is to say a single disturbance, a mid-level class which incorporates a low-level disturbances collections and finally, a high-level class where several mid-level groups are included [site, 1.2*].
Duration and intensity??
Chapter 4. Perturbations and operational strategies
Perturbations
As an outcome to the previous chapter related to disturbances, this chapter will present the perturbations. That is to say, the effects of disturbances on the entire airspace and ATM system with respect to delays, system cost losses, environment or airspace users dissatisfaction.
?? Depending on how much the external or internal changes makes the system divert from its initial state, on a large scale perturbations can be transient, with consequences on a short period of time or permanent, with a significant impact over time that will lead to a new system state. [3*] The next figure express the already mentioned types of perturbations.
Figure – Impact of a disturbance on an ATM System [pdf 1.3]
In order to realize how significant the perturbation is, a throwback look in the first chapter is required, where performance indicators are mentioned. Based on these performance indicators, with the biggest impact on areas such as safety, capacity, cost efficiency and environment, experts provides a classification of perturbations, allocating them in scale like: large negative, small negative, negligible change, small positive and large positive.[site, 1.2*]. For a better understanding, a briefly presentation of what each of these categories consists of will be presented. It will concern the impact with respect to performance system.
From a safety point of view, things are clear. From a large negative to a large positive scale, the former express a high accident/incident probability (more than a factor 2) that slightly continues decreasing until the percentage is substantially diminished by reaching large positive scale. When talking about the capacity of a certain airspace sector or airport it is considered for large negative class a reduced capacity for a major period of time. As for small negative and small positive, the capacity is decreased, respectively increased in a lower degree for a short time. Large positive suggests a significant rise in the airspace capacity with more than 30%, while negligible means there is no effect on capacity. In terms of cost-efficiency it could be mentioned the economical aspect since the previously cited scale represents supplementary costs (large negative) or cost savings (large positive) for the airliners and the Air Navigation Service Providers (ANSP). Here, the costs could be for several airplanes in case of large negative and positive and just for one airplane or a few of them in case of small negative and positive. Negligible implies no modification on costs. Passing on the environment area, further emissions and noise are indicated through the large negative class that take notice of the airplanes that are flying for a long period of time at lower altitudes. On small negative class only one or few aircrafts are involved when the pilot needs to fly additional miles. Finally, it could be remarked a reduced impact on the environment on small positive and large positive, as well as no other consequences in the negligible class.
In terms of costs, disruptions outcome in additional costs for the airlines and the airports. Most operations costs are given in cost per hour for all phases of the flight from arrival, departure, ground movements or hold on procedures. For aviation companies and the ATM system, delays and cancellations are a huge and expensive issue. A simple delay in the embarking process of passengers and crew may lead to other delays, therefore in a waste of money.
As presented in the book of Andrew Cook, ‘Complexity science in Air Traffic Management’, traditional airlines operating hub and spoke networks and low cost airlines with point-to-point networks are inclined to produce less optimal trajectories, delays and rerouting. For example, low-cost airlines are shown to be the main contributor to path redundancy, which increases the flight options passengers have between a given origin and a destination airport.
Framework of strategies and properly reactions
This part of the project tries to present and understand the way disturbances are detected in the ATM system, who are the ones that shall firstly observe the disturbance and what are the measures taken immediately after the problem had been established. Based on some controllers and pilots interviews (MAREA Interviews – Stroeve et al., 2011 – presented on a research study regarding resilience) {1.2/pg 20}, several ideas can be expressed, as follows.
To begin with, the disturbance must be identified. This can be done through either a pilot, a controller, a system alert or any other person involved in the air traffic system like someone from the airport operations, maintenance operations, cabin crew etc. The notification of a disturbance can come even from different sources at the same time. Nevertheless, the top of the list it is held by controllers and pilots as being the first ones that realize a disturbance and to a smaller degree all the others.
Next, another important step needed to be taken is to establish communication with the pilots, other airports, airspace sector controllers, airlines and so on in order to make everyone aware of the disturbance and the perturbations that comes with. By everyone, it can be understood the entire air traffic system. Through this measure, an exchange of instructions and information is held, by which the new airspace management configuration can be reported. Due to the conditions created by the disturbance and the importance of perturbations, this configuration can mean restrictions, a close airspace or runway, a rerouted traffic on other airports or others. In unexpected conditions it is absolutely necessary to exist this interchange of information that has the role to facilitate all the monitoring, organizational and control actions. Thus the air-ground communication must be mentioned (between the air traffic controller and the pilot) which is the first approach done and to a smaller extent follows communication between controller and several control and organization facilities, and to even a smaller degree the air to air communication between pilots follows. Therefore, a safe and orderly air traffic in sudden situations and emergencies is basically depending on a transparent internal communication, as well as on the ability of the human involvement (within the ATM system) to quickly shift and adapt with the correct reactions.
In order to adequately handle the unexpected situations, there are some strategies and procedures that must be respected. When talking about human performance within the air traffic management system, the strategies differs from controllers to pilots as well as the way they are applied. The differences comes in the organisational tasks, in the reactions to sudden situations, the procedures each entity must follow and their interventions when dealing with disturbances. An ATC-pilot interaction must continuously be active for the best coordination in implementing the strategies. If there is a crisis situation such as a volcanic eruption or severe weather in different parts of world, the controllers must cope with the new air traffic network and direct all flights in other airspace sectors. It is also important to raise the number of controller under that certain period of time so that the whole traffic could be maintained at a certain level of safety.
When such disruptions take place, the Network Manager has the responsibility to monitor and prevent disruptions events turning into crisis events. In order to minimize them and to avoid a potential infrastructure fail of great significance it is essential to exist procedures, an actual plan of measures based on preparation and rehearsal and a strong interconnectivity between the state entities, airport authorities and airline companies. This is why the European Commission and EUROCONTROL established a Crisis Management Unit to be prepared to response both politically and nationally or internationally. [EUROCONTROL, 11*]
In a pre-alert phase, minor disruptions may be detected, but several others are forthcoming. The Network Manager becomes aware of the consequences this may have on the airspace sector and keep an up-to-date monitoring situation. In case the system does not recover its normal state due to the perturbation it will be dispatch to the next phase related to disruption management. Here the event is already amplified and it may proceed to a crisis management phase. Related information are made public on the NOP (Network Operations Portal). In the crisis phase, considerably events such as an armed or cyber-attack may arrive in a major perturbation on the entire air transport network, with a gap between the capacity and demands. The EACCC (European Aviation Crisis Coordination Cell) is alerted in order to intervene, to settle and supply the communications and inform all the relevant authorities and entities. It must be clarified that for all phases certain measures of facilitating the communications are taken (e.g. teleconferences). [EUROCONTROL, 11*]
At an organizational level of the air transport system, concerned structures responsible for a safe and orderly air traffic flow, are important to be mentioned like EUROCONTROL, EASA, Air Navigation Service Providers, National Supervisory Authorities (NSA), airline and airport entities, private operators. Through their involvement and role in the coordination and supervision of operational flight phases it can be assessed the operational control during a challenge serving a disruption.
CFMU is the ………. It represents the structure that handles the slot allocation as well as the CTOT (Calculated Take-Off Time). These means that any disruption in the system with repercussion on the normal/logical order of a flight phases will upset the CFMU pre-tactical or strategic planning.
In spite of the fact that rules and procedures plays an important role in coping with ordinary or uncommon conditions, this presentation aims to bring to attention also the human operators flexibility framework. This analysis will expose to what extent the human performance influence the resilience of ATM system….
Chapter 5. Measures and metrics
Time and magnitude metrics
As mentioned before the objective of this study paper is the analysis of the ATM system with respect to the resilience in order to bring improvements and achieve a more robust system state, one which must be able to adapt its behaviour to unforeseen situations, such as a perturbation in the environment, or to internal dysfunctions in the organisation of the system. [site, pdf1.1]. But before investing resources in the system, it is necessary to know how resilience can be measured, what are the parameters needed to be taken into account and where are the weak points of the system. Such, for a complete investigation certain steps must be carry on.
Define and describe the system, one would like to investigate, and its boundary to the environment;
Specify the scale and/or the level of hierarchy at which the system will be observed;
Define the set of performance indicators describing a state of the system and the validity period of the set;
Specify the reference state of the system by means of the defined set of performance indicators and the validity period of the reference state;
Indicate and classify disturbances, which impact on the described system one would like to investigate, by type (of effect), frequency, intensity and duration (keeping in mind that the scale in which the system is defined and observed is the most important factor determining the level of detail required in characterizing disturbances and their impact on the system
For each selected disturbance set the time horizon for investigation of resilience or robustness of the system against the disturbance
[pdf 1.3 – page 14]
We define a metric as any quantitative metric, particularly one which usefully express some output of a system (usually performance), part of the system, or an agent within it, usually over an aggregate scale and often as a ratio (e.g. per flight) [ACBook]. With respect to the state condition of a system and the behaviour of the ATM system during a certain disruption, one can measure the resilience based on the deviation in magnitude and time.
Depending on a defined reference state, the deviation of the actual state of the system from its reference state over time as well as the magnitude of the following fluctuations, after a disturbance has occurred, are used to evaluate resilience of the system [site, pdf 1.3].
This can be done considering two important elements when talking about a disturbance in a system. That is to say the time of deviation denoted and time of recovery as . By ‘time of deviation’ it can be understood the time until the system achieve its maximum point of difference measured from the point the system exceeds its reference state, while the ‘time of recovery’ can be defined as the necessary time the system need to turn back to its initial state. Based on the relation between the two parameters it is established certain categories of resilience (high, medium or small resilience) as the following graphs stand as proof.
Figure – High resilience of an ATM System against a disturbance [pdf 1.3]
Figure – Medium resilience of an ATM System against a disturbance [pdf 1.3]
Figure – Low resilience of an ATM System against a disturbance [pdf 1.3]
As it can be seen in the figure no…, the time of deviation is greater than the time of recovery
() resulting in a high ATM system resilience. When we speak about medium resilience it can be understood an equivalence between the two parameters (), while a low ATM resilience have the time of deviation smaller thus the duration of recovery (). [pdf 1.3*].
Let us consider an airport as an ATM System, the throughput of its runway system as a set of performance indicators that defines the state of the system , the throughput
as a reference state and a winter season as a disturbance.
Let us assume that the time horizon for the evaluation of resilience or robustness of the system is the length of the winter season . When the airport performs so that its current state is at the reference state over,i.e. the airport ܣ has the throughput over the considered period of time, this means that it has no stress during . Therefore, the system is robust against the disturbance during the time horizon (see framework in Figure 1). However, this situation is possible at the airports working under its nominal capacity only. More realistic is that the throughput becomes smaller, for instance
This means that the considered system – the airport – is under stress over the time horizon . However, the system returns back to the reference state at the end of the time horizon . So, it reacts by survival stress and acts by transient perturbation over . Therefore, the airport is resilient against the disturbance over the time horizon .At the case, if the evaluation of resilience or robustness of the system is performed during the time horizon , which is shorter than , and the throughput of the system is , the system is not resilient over the time horizon . There are two possibilities over :
the system is under survival stress and reacts by permanent perturbation – a new reference state of the system will be specified (for instance, )
the system is under lethal stress, i.e. the throughput cannot be accepted – the system will be modified (for instance, the relevant airport equipment will be adjusted).
This example stresses the importance of the time horizon for evaluation of resilience or robustness of an ATM system.
[pdf 1.3-page 11]
General resilience metrics based on performance
This part of the study aims to measure and determine resilience of ATM system. Resilience metrics will be expressed in formulas, while some disruption cases will be used to observe the evolution of events before, during and after a disturbance. Since the subject covers a large spectrum of disturbances, further analysis will be provided only for part of them. The most important disruptions appeared in the ATM system of Europe with significant impact resulted in delays, closed airspaces and changed trajectories will make the sight of this chapter. Perturbations in air traffic will be considered in terms of performance and capacity and examined in 3 phases: locally, nationally and for Europe network. For appropriate analysis, several data sources were used, consisting of different literature, statistics and EUROCONTROL reports.
Based on a detailed analysis on the resilience metrics obtained from other domains literature like psychology, infrastructure system, ecosystems and so on, resilience can be expressed in terms of ‘triangle resilience’ using the next formula:
This new concept of ‘triangle resilience’ emphasize the impact of a disruption on a system performance and the recovery line model drawn, by taking into account
the time of disruption (),
time of recovery (),
the peak time of full perturbation within a system () and
the performance.
If the pattern of the triangle decrease in depth and duration, it means that we have a high system resilience.
An extended formula used for quantifying resilience in represented below:
where = is the system performance before the disruption
= is the post-disruption performance level
= is the performance at a new stable level after recovery efforts have been exhausted
= express how fast the system can recover
….
When it comes about the entire air transport network, Janic (2015) propose a resilience indicator defined as “the ratio of the on-time and delayed flights achieved to the total number of scheduled flights during a specific time period.” He consider that the air traffic network resilience could be measure by the resilience sum of the each singular airport.
The already mentioned formulas of resilience are used to express in terms of probability how a system react in case a disturbance or several disturbances took place and how fast the system can return to its original performance. Through such resilience assessments one can evaluate the systems problems and model different scenarios dimensions and implications in order to prevent uncertainty level of disruption.
For a comprehensive view of resilience it is proposed a discussion on the interdependencies between systems that will expose the vulnerability of air transport system. The concept defines how a group of two or more subsystems rely on the others towards a resilient infrastructure. The interdependencies highlight an important aspect that is the sustainability of a system from a social, economic and environmental point of view. In normal operations, interdependencies may not be under attention, but once a disruption event happen, they become evident and undeniable important. It can be then mentioned 4 types of interdependency stated by Rinaldi (2004):
Physical interdependency refers to a material dependency of 2 systems.
Cyber interdependency express dependence on the information exchange.
Geographic interdependency is related to the environment context.
Logical interdependency denote any other dependency of a system on the other one.
In aviation, there are several correlations on multiple levels. A simple example may be illustrated by the interdependency of airlines and airport. If certain airspace sectors or airports are closed for any reason, this will outcome in cancelled flights and passengers unable to board for the airline companies.
Next, several airports resilience calculations will be undertaken at different levels in order to draw some conclusions about the Air Traffic Management system from a resilience point of view. When talking about the air transport system, one can characterize the performance of an airport (Q (t)) through capacity, demand and delays/rerouting.
In this chapter, three case-studies will be closely analysed in order to bring under examination resilience at a local level (for a single airport), national level and for the entire air traffic network in Europe. Firstly, …. Airport will be studied for local resilience. Next, ROMATSA air traffic controllers strike from 30th of May, 2017 will be represented at a national level and lastly, the third case study will follow the line of Iceland volcano eruption event, from April, 2010.
Case study 1:
This case study presents resilience metrics at a local level that is for a single airport. Once a disturbance took place, the perturbations propagates among the network, causing delays after delays in air transport due to the interdependencies between the nodes. Normally, the effects of disruption keep going on a certain period of time. If the timescale exceed some limitations, the disruptions becomes noticeable. Using the capacity and delays as parameters, the next metrics will determine if there are any significant effects on the air traffic network produced by a disruption on a single airport.
Where = an airport
= the capacity of the airport a
= local delays at the airport
= total demand at the airport
= local delay generator
= total demand at the airport a
= time window
= all time windows
In order to move forward “the breaking point” of an airport will be defined “as the critical airport capacity value in which there is a sudden and sharp increase in total delay”. [pdf 3.3]
Efficiency of an airport is another important concept illustrated as follows:
The following metrics are used to establish the percentage of flights on an airport “a” that has a rate of delays of over 15 minutes. It is stated that if this percentage exceeds the number of 20, then significant delays will be generated in the network [pdf 3.3].
Where = flight
= scheduled time of departure for flight f
= scheduled time of departure for flight f
= all scheduled departure flights
= all scheduled departure flights
= represents 15 minutes of delay
Thus it will be obtained:
Where = flight
= flights that has a delay of more than 15 minutes expressed in percent
Such analysis on resilience of Air Traffic Management implies a debate on comparisons between system scenario at its normal performance and the system scenario when this is affected by disturbances generating propagation of the system degradation in the network. [pdf 1.3*]
Case study 2: ROMATSA air traffic controllers strike, 30th of May 2017
This case study aims to observe and analyse the impact of air traffic controllers strike from ROMATSA (Romanian Air Traffic Services Administration) Headquarter on the Romanian airspace and the air traffic network. This is one of the most recently event of large-scale in our country, that took place on 30th of May, 2017. According to the legislation, one third of the flights will be provided with air traffic services, while the rest of them will be cancelled or rerouted. The strike had a duration of 2 hours and it brought economical losses for our country, since every airplane that cross our airspace have to pay a route charge considering the distance length, the applied charge per unit and the weight of the aircraft.
It started at 9:00 a.m. and ended at 12:10 a.m. Even though 2 hours may seem a short period of time, when air traffic is involved it means several delays and cancelled flights over the day, many hours after the strike concluded. Some of the following figures will provide a better view of the consequences the strike had over the increased capacity of our neighbouring countries.
Firstly, a table will be presented containing the number of flights that cross the Romanian airspace at certain time during the day the strike took place, that is 30th of May, 2017. The time period was chosen for 1 hour distance and is expressed in both Local Time of Romania and UTC Time.
**UTC is the Universal Coordinated Time is the standard time used in the entire world.
Table … – Flights in the Romanian airspace during and after the strike
9:00 a.m. (Local Time) – The air traffic controllers strike started and the effect could be seen already. 3 flights were cancelled and 2 others for Frankfurt and Amsterdam have delays.
10:00 a.m. (Local Time) – The strike continues. Now the Romanian airspace has only 5 flights in control as it can be seen in the following picture. All the other flights were rerouted, most of them south of the Danube, through Bulgaria, were an increase in the capacity can be easily observed. During the strike, air traffic control was taken over by EUROCONTROL.
Figure … – Screenshot Flight Radar 24: Romanian airspace at 10 a.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 11 a.m., 30th of May, 2017
12:30 a.m. (Local Time) – The air traffic controllers strike ended at 12:10 p.m., the controllers return to work and the Romanian airspace is opened again. By now, several flights were cancelled and delayed, creating flurry through the passengers. Even though the strike ended, at 12:30 p.m. the consequences over our neighbouring airspaces can still be seen. Next picture shows an increased number of flights, especially in Bulgaria, Serbia and Hungary. All the flights passing Turkey are rerouted south of Romania.
Figure … – Screenshot Flight Radar 24: Romanian airspace at 12:30 p.m., 30th of May, 2017
The following figures shows the air traffic flow over the Romanian airspace that come after the strike. It will be noticed how fast the flights will be resumed and how much time it is necessary for the air transport system to return to its normal performance. A time period of 1 hour had been chosen to keep under observation the airspace, until 10 p.m.
Figure … – Screenshot Flight Radar 24: Romanian airspace at 1:30 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 2:00 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 3:00 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 4:00 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 5:00 p.m., 30th of May, 2017
6:00 p.m. (Local Time) – At this hour the air traffic stabilizes and in the Romania airspace can be counted roughly 53 flights.
Figure … – Screenshot Flight Radar 24: Romanian airspace at 6:00 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 7:00 p.m., 30th of May, 2017
8:00 p.m. (Local Time) – Air traffic flow in Romania neighbouring countries decreased. Romania is crossed at this hour by 36 flights, more than half of the normal capacity.
Figure … – Screenshot Flight Radar 24: Romanian airspace at 8:00 p.m., 30th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 10:00 p.m., 30th of May, 2017
In order to outlook the differences in air traffic over Romania airspace during the strike and several hours after the strike, some figures and estimating numbers will be presented for the day after the event, that is for 31th of May, 2017. For this case, a time period of 1 hour was also chosen, starting from 10 a.m. up until 5 p.m. (Local Time).
Table … – Flights in the Romanian airspace; the day after the strike
Figure … – Screenshot Flight Radar 24: Romanian airspace at 10:00 a.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 11:00 a.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 12:00 p.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 1:00 p.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 2:00 p.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 3:00 p.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 4:00 p.m., 31th of May, 2017
Figure … – Screenshot Flight Radar 24: Romanian airspace at 5:00 p.m., 31th of May, 2017
Considering the previous data and a normal capacity over the entire Romanian airspace of 80 flights crossing Romania in an hour, including landings and take-offs, that is a 100% initial/stable performance level, it can be estimated the performance level in percentage during the disruption and hours after. Using the rule of three, calculation will be performed.
Where x = performance level obtained [%]
n = number of flights/capacity
Therefore, the following results will be obtained for the 30th of May, 2017, the day of the air traffic controllers strike.
Table … – Calculations related to performance levels during the day of disruption
Thus, the resilience of ATM system …….
Case study 3: Eruption of Iceland's Eyjafjallajökull volcano, April – May 2010
Figure …- Eruption of Eyjafjallajökull volcano – Institute of Earth Science [http://earthice.hi.is/solofile/1015805] [http://futurevolc.vedur.is/?volcano=EYJ#]
Eruption of Iceland's Eyjafjallajökull volcano on 14th of April 2010 is one of the most important international event with major social, economic and environmental impact, especially on the worldwide air transport. The ash cloud resulted from the eruption produced several disruptions consisting in several closed airspaces, thousands of cancelled flights and millions of passengers affected. Even though the crisis period was during the first 8 days after the eruption (14th – 22nd, April), the effects of the disruption could have been seen up until mid-May.
One of the biggest problem was represented by the ash cloud containing high ash concentration levels that was moving towards Europe causing large airspace sectors closure. The eruption outcome in an expel of 250 million cubic metres (0.25 km3) tephra into the atmosphere that raise up untill a height of 9 km (5.6 miles). There were very fined grained of ash of 10 μm according to the Institute of Earth Sciences that examined the samples from 50 km away from the eruption site. [http://www.coolgeography.co.uk/A-level/AQA/Year%2013/Plate%20Tectonics/Volcanoes/MEDC%20case%20study.htm]
The magnitude of this event, caused especially by an accelerated rate of ash spreading and a long time period of persisting ash, the Iceland volcano eruption becomes the highest level of air travel disruption since the Second World War [https://en.wikipedia.org/wiki/2010_eruptions_of_Eyjafjallaj%C3%B6kull] Statistics shows a number of 104,000 cancelled flights during the April crisis, 10 million passengers that were not able to get onto their flight, 20 countries forced to close their airspace sectors and the consequences continues on the next month with a number of roughly 7,000 cancelled flights on May. This could be expressed in a percentage of 48% of expected traffic during the 8 days of the main period of the disruption. [EUROCONTROL REPORT – April-May, 2010] During May, the event and consequences over the air transport network were accentuated by Greek general strike that took place 5th May2010, numbering through delays and cancelled flights another 1,000 affected flights.
The next table represents the effects of disruption in air traffic over the Europe. It provides estimated numbers of flights in Europe for several days before (8th April – 13th April), during the main period of disruption (14th April – 22nd April) and after the disruption (23rd April – 25th April).
Table … – Number of flights in Europe before, during and after the April disruption.
[EUROCONTROL REPORT]
Based on the previous data, the next figure shows a graphic expressing the impact of Iceland volcano eruption on air traffic across Europe network in a certain period of time. Through this graphic the resilience of the system is emphasized relying on the number of flights and on time that will help building the so called ‘resilience triangle’.
Thus the three important time dates, the time of disruption, the peak time of disruption and the time of recovery will be mentioned again. It could be noticed a steady capacity during the days before the eruption with a slightly decrease on 10th April. On the 14th of April, the time of disruption the eruption of volcano took place and from there it could be easily observed a steep fall in air traffic capacity over the entire Europe. The moment of full performance impact was established on 18th April, when the number of flights across Europe was of 4,975 as it could be seen in the previous table. This could be encompass in a total loss of 80% of the normal traffic during the most affected day. 22nd April represents the date when the system starts to get back on its stable line, even though the repercussions on the air transport in terms of delays, cancelled flights, economic and social impact continued up until 17th May 2010.
Figure … – Graphic of air traffic in Europe before, during and after the disruption, April 2010.
[EUROCONTROL REPORT**]
The resilience of the Air Traffic Management system could therefore be reduced to the following graphic:
Figure … – Graphic of disruption and recovery, April 2010,
Eruption of Eyjafjallajökull volcano event
Where = performance of the system
= stable performance of the system
= the minimum performance of the system after the disruption
= time of disruption, on 14th April
= peak time of disruption with a full impact on performance, on 18th April
= time of recovery, on 22nd April
Between and it is represented the degradation slope of the system performance;
Between and it is represented the recovery period of the system performance, until it reach the stable F(t).
Complex system involves networks and the network involves subsystems. In order to point out the behavior of each individual component and to outlook the most affected airspace sectors from the network, further analysis will survey the resilience of the countries from Europe during the main period, from 15th up until 22nd of April.
The next table presents the estimated cancelled flights in percentage per days for a list of countries from Europe.
Table … – Estimated percentage of cancelled flights for each European State, between 15th – 22nd April
[EUROCONTROL REPORT]
In top 3 of the most affected countries are Ireland, United Kingdom, and Finland, with a percentage of flight cancellations of over 90% during 5 days. The biggest impact could be seen on the Finland region where the overall cancellations reached a percentage of 81% that could be expressed in more than 4,000 flights including internal ones, arrival, departures and overflights. It is closely followed up by the Ireland which established a 100% cancellations during 2 consecutive days on 18th-19th May and an overall of 74 percent. United Kingdom also recorded an overall loss in flights of 74 percent, being the third most affected country, presenting a high rate of cancellations during the first 6 days of the disruption main period. Even though the volcano eruption was in Iceland, the airspace capacity over the country did not suffered a high rate of flights loss, Iceland being able to still keep flights to North Atlantic in the first days after the eruption. The reason behind this is related to the ash cloud which was straightened through the south.
Representation of disruption on air traffic in Europe using geodetic maps
Figure … -14th of April 2010, Ash cloud – Iceland volcano eruption [http://news.bbc.co.uk/2/hi/europe/8634944.stm]
Figure … – 20th of April 2010, Ash cloud – several days after Iceland volcano eruption [http://news.bbc.co.uk/2/hi/europe/8634944.stm]
Conclusions: “Overall, these eruptions have prompted the aviation industry, regulators, and scientists to work more closely together to improve the manner in which hazardous airspace is defined, forecast, and communicated.” [https://volcanoes.usgs.gov/volcanic_ash/ash_clouds_air_routes_eyjafjallajokull.html].
Through this case-studies it is desired to raise awareness on the ATM system resilience for future improvements and new ways of network recovery in the interest of a more reliable system. …
Traditional approaches of recognizing and interpreting the individual system components are not enough to fully describe the framework of essential properties of a complex systems. Such frameworks of system behaviours cannot be anticipated only through local analysis, but from the connection between the subsystems.
ATM modelling approach
Being such a complex system, it is required a modelling approach ATM system investigation through which the system will be simply split in two sector: the human related aspect along their actions and the physical movement of the aircraft. These implies the decision-making process since the motion of the airplane depends on both the decision taken by the pilots in unexpected situations and its performance indicators.
Such an approach could be found in the AirTOp (Air Traffic Optimization) Simulator used by the EUROCONTROL Experimental Central (EEC) to determine some measurements with respect to the key performance indicators and area mentioned in the previous chapters. The platform offers the possibility to tackle scenarios in the Departure, En-Route, Approach and Airport Ground Movements through a 2D/3D map interface. [http://www.eurocontrol.int/articles/airtop-fast-time-simulator *]
A simple example serves to illustrate the principle of the modeling approach. An aircraft delayed because of resource shortages during the turnaround process at the airport will receive a new slot by the air traffic flow manager. Ground- and runway controller are guiding the pilot till the ATC takes over. Because of weather disturbances, a sector controller might chose a trajectory different to the one originally planned (the red respectively blue dotted line in Figure 8). Any decisions occurring during this flight leg should be traceable in the hierarchical structure. [pdf 1.3 page 17]
For modelling the transport flow and congestions in uncertainty conditions, the Nagel-Schreckenberg model was realized for road transport, which was further used in air traffic at to model ground congestion at the Tokyo International Airport [CATM16]. These models are based on traffic jam modelling through a detailed analysis on the drivers conduct on the streets.
Chapter 7. Means of system improvements
In the last years, several actions and future technologies approaches were undertaken in order to adapt the air traffic sector to the continuous growth. One of the organisations that deals with these kind of initiatives is SES (Single European Sky) that pursue to improve safety performance by a factor of ten, to reduce the cost of ATM by a factor of 2, to reduce the environmental impact of an individual flight by 10 per cent and to cope with a threefold increase in traffic (A.C.B, page 3). Also a reduction in the environmental effects is aimed. The air transportation stakeholders like the Air Navigation Service Providers (ANSP) the airports, the airlines, the aircraft and ATM equipment manufacturers/suppliers will be involved in the process of building a new ATM system [pdf4.1*]. Another organisation that was settled in order to manage certain applied researches regarding the improvements and modernisation of the European ATM is the SESAR Joint Undertaking (SJU) that fulfil the SES objectives. [ACB*]
Such, this chapter of the paper aims to identify future concepts of Air Traffic Management towards a more resilient system that will perform optimal operations under any circumstances, including uncertainty conditions. Firstly, some of the main problems causing inefficiency in the air transport system will be established, then new methods of improvement will be determined for a new infrastructure system.
Impediments in the future ATM infrastructure
One of the important aspects considered to be major issues in the future ATM systems is the increased capacity of certain airspace sectors and airports. Predictions show a 20% growth in the airports capacity compared to the 2005 and over 80% in the airspace capacity. This reveals future delays and congestion problems on the nodes of the network (airports) that will be saturated. As a consequence of that, the air traffic controllers will be overloaded, the aircraft will not be able to take-off, the environment will be degraded due to extra emissions from the fuel burning, and passengers will be annoyed by delays, therefore there will be extra expenses.
Related to the capacity problems it could be mentioned a significant increase in the demand that will lead to airspace capacity limitations and a loss of system efficiency. Through this restrictions, the flights will be rerouted, forced to wait on the ground or do a hold procedure that implies extra fuel consumption and more expenses. Route charges will also influence the future ATM system in terms of costs and regulations.
Concepts towards a resilient and efficient Air Traffic Management System
In terms of research and improvements brought to the ATM system, a four dimensional (4D) trajectory planning may serve as a potential change having in sight the reduction of ‘traffic bunching’ in en-route and terminal areas. [ACB*] The 4D trajectory incorporate the 3D trajectory and consider as the fourth dimension the time parameter. Based on models and algorithms, optimized trajectories are provided for all phases of operations taking into account all constraints. Through this concept it is hoped to attain a high level of predictability and efficiency that will allow the air traffic controllers to cope and respond safely to the air traffic demand. Other benefits are related to the cost-effectiveness and a reduced percent in emissions.
The current ATM system presents some concerns in terms of information exchange and flexibility. In order to improve this drawback, the System Wide Information Management concept is proposed. Switching over from point-to point communication to a net centric communication it supports the interoperability of the system providing access to weather and flights data, airport operational status and data concerning use of airspace [FASW7]. These information will be available for all the operators increasing proper decision-making at the right moment, thus the efficiency of the ATM system.
Nowadays, the borders and the fragmentation of the airspace cause delays and constraints in reaching a productive and efficient air traffic flow. The flights have to travel more kilometres on longer routes due to restrictions leading to additional costs for the airlines. According to statistics the costs of such a discontinuity in air traffic flow in Europe is evaluated at $1.3billion every year. Apart from that $4 billion are spent every year because of delays and 429 million unneeded extra flight kilometres. [ATAGr]. Therefore, there is a necessity in attaining a restricted airspace, where national borders will not be a drawback anymore, instead direct routes …
Cost aspect of resilience
With respect to the cost-related aspect, increasing the resilience of a system and the necessary time for development as to join other transportation framework require further expenses. …….
Figure … – Recovery variation under different recovery strategies [EOR14]
Resilience is desirable but requires extra cost and effort and conflicts with global economic pressures to increase efficiency and related low operating costs essential for survival in modern firms. [http://discovery.ucl.ac.uk/1469381/1/131-135.pdf]
Chapter 8. Conclusions.
Methods to achieve resilience include 1. Redundancy: duplication and diversification which replace parts that go wrong, and (in natural systems) species which have overlapping roles and niches, e.g. multiple forms of power generation serving overlapping parts of a city, and 2. Low dependence on human inputs which is desirable since it reduces interference with resilience. [http://discovery.ucl.ac.uk/1469381/1/131-135.pdf]
[INTREBARI]
SESAR?? SESAR Project POEM
Working Plan
Introduction. Statement
Resilience of the system. Resilience applied on Air Traffic Management System
Problem framework. Disturbances. Prediction of disturbances
Perturbations. Consequences and the impact on ATM system and flight operations
Measures and metrics.
Representation of the disturbances and perturbations using graphs
Means of system improvements
Conclusions.
Bibliography
References
[1] [CATM16] Cook Andrew, Damian Rivas, 2016. Complexity science in Air Traffic Management Book
[2] [] EUROCONTROL, 2009, Cooperative Network Design. A White Paper on Resilience Engineering for ATM
[3] []Gluchshenko Olga, 2012. Definitions of Disturbance, Resilience and Robustness in ATM Context. German Aerospace Center (DLR), Institute of Flight Guidance
[4] [] Andrew Cook, Henk A.P. Blom, Fabrizio Lillo, Rosario Nunzio Mantegna, Salvatore Micciche, Damian Rivas, Rafael Vazquez, Massimiliano Zanin, 2014. Journal of Air Transport Management, Applying complexity science to air traffic management.
[] [] Gluchshenko Olga, Foerster Peter, 2013. Performance based approach to investigate resilience and robustness of an ATM System. German Aerospace Center DLR, Institute of Flight Guidance
[5] [] ICAO, Doc 9883, 2009. Manual on Global Performance of the Air Navigation System. Appendix D
[1.1] [] Robert Francis, 2013. Analysis of resilience in manmade and natural systems. Resilience2050.eu
[1.3] [] Gluchshenko Olga, Foerster Peter, 2013. Setting the basis – Defining resilience in the organization of ATM. Resilience2050.eu
[1.2] [] Stroeve Sybert, Bas van Doorn, Everdij Mariken, 2013. The Human Contribution – Analysis of the Human Role in Resilience in ATM. Resilience2050.eu
[9] [] [EUROCONTROL, CODA, 2017] EUROCONTROL, CODA DIGEST, 2016. All-Causes Delay and Cancellations to Air Transport in Europe. Site web: http://www.eurocontrol.int/sites/default/files/content/documents/official-documents/facts-and-figures/coda-reports/coda-digest-q4-2016.pdf
[2.1] []Zanin Massimiliano, Ureta Hector, 2013. Description of the integrated database schema. Resilience2050.eu
[2.2] [] Menasalvas Ernestina, Muelas Santiago, 2013. Description of the ATM patterns and insights discovered. Resilience2050.eu
[2.3] [] Menasalvas Ernestina, Muelas Santiago, 2014. Specifications and procedures to support the design of a resilience data mining service. Resilience2050.eu
[3.1] [] Innaxis, 2013. Resilience multilayer representation. Resilience2050.eu
[3.2] [] Innaxis, 2013. The resilience metrics for the European ATM system. Resilience2050.eu
[3.3] [] Innaxis, 2015. New design principles to foster safety, agility and resilience. Resilience2050.eu
[4.1] [] DHMI Genel Mudurlugu, 2014. Concept for the new, efficient Air Traffic System. Resilience2050.eu
[] Network Operations Portal. Site web: https://www.public.nm.eurocontrol.int/PUBPORTAL/gateway/spec/
[6] [] Met Office. Site web: http://www.metoffice.gov.uk/aviation
[7] [] http://sesarinnovationdays.eu/files/SIDs/SID%202011-MAREA.pdf ??
[8] [] Skybrary. Human error types. Site web: http://www.skybrary.aero/index.php/Human_Error_Types
[10] [] [EUROCONTROL,10] Tools available in times of disruptions and crises. Site web:
https://www.eurocontrol.int/articles/tools-available-times-disruptions-and-crises
[11] [] [EUROCONTROL,11] What could impact the network? Site web: https://www.eurocontrol.int/articles/what-could-impact-network
[] F. Gargiulo, D. Pascarella, A Errico, V. Di Vito, E. Filippone, 2014. Resilience Management Problem in ATM Systems as a Shortest Path Problem. Site web: http://www.sesarju.eu/sites/default/files/documents/WPE/sid2014/SID_2014-29.pdf?issuusl=ignore
[f] [EUROCONTROL Report] STATFOR, Doc394, EUROCONTROL, 2010. Ash‐cloud of April and May 2010: Impact on Air Traffic.
[] Coolgeography.co.uk. Volcanoes case study – Eyjafjallajökull. Site web: http://www.coolgeography.co.uk/A-level/AQA/Year%2013/Plate%20Tectonics/Volcanoes/MEDC%20case%20study.htm
Economic Impact of Air Traffic Control Strikes in Europe, 2016. Site web: http://www.politico.eu/wp-content/uploads/2016/10/ATCimpactreportA4E.pdf
Skybrary, Regulation (EC) No 552/2004 of the European Parliament and of the Council, 10 March 2004. Interoperability of the European Air Traffic Management network. Site web: http://www.skybrary.aero/index.php/Regulation_552/2004_-_Interoperability_of_the_European_ATM_Network
SESAR, 2015, European Organisation for the Safety of Air Navigation. The roadmap for delivering high performing aviation for Europe. European ATM Master Plan. Site web: https://ec.europa.eu/transport/sites/transport/files/modes/air/sesar/doc/eu-atm-master-plan-2015.pdf
[EOR14] Eric D. Vugrin, Mark A. Turnquist, Nathanael J. K. Brown. (2014). Optimal Recovery Sequencing For Enhanced Resilience And Service Restoration In Transportation Networks.
[ECTL08] EUROCONTROL, August 2008. Stakeholders Influence on the ATM Strategy Development.
Skybrary. 4D Trajectory Concept
[FASW7] Federal aviation Administration. System Wide Information Management
[ATAGr] Air Transport Action Group, 2012. Revolutionising Air Traffic management. Practical steps to accelerating airspace efficiency in your region
Sarah Sheard, 2008. A framework for system resilience discussions. Stevens Institute of technologies.
[HRE12] Erik Hollnagel, Jean Pariès,John Wreathall, David D Woods, 2012. Resilience Engineering in Practice: A Guidebook
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