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Sector Over-Deliveries Due to Non-Adherence

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Category: Safety Alert Safety Alerts
Content source: EUROCONTROL Safety Alerts EUROCONTROL
Content control: EUROCONTROL EUROCONTROL

Request for Support Message

Sector Over-Deliveries Due to Non-Adherence

Date: 25 May 2009 Request for Support Message.gif

Your Support Is Required

The aviation safety professionals, particularly Aircraft Operators and Air Navigation Service Providers, are kindly invited to share experience and good practices regarding the below mentioned issue.

Synopsis

  • Daily across Europe, traffic regulations are put in place to protect ATC sectors from receiving more traffic than the controller can handle safely. However, it happens that more aircraft than planned enter these protected sectors, exceeding their capacities by more than 10%, which is regarded as an ATFCM “over-delivery”.
  • EUROCONTROL has launched a campaign to raise awareness amongst controllers, pilots and flight dispatchers about Flight Plan and ATFCM adherence. It ranges from ATFCM slot adherence, provision of accurate EOBT/CTOT to the en-route stage of flight, e.g. FL changes and use of DCT.
  • The link below will guide you to the downloadable version of the “Flight Plan & ATFCM adherence” booklet.

Analysis

When investigating the reported occurrences of over-delivery in most cases it is found that additional flights entered the concerned sector as a result of:

a) Not flying at the requested flight level (RFL); or,
b) Departing at times different from the original estimated off-block time (EOBT) or calculated take-off time (CTOT); or,
c) Arriving in the sector earlier or later than originally planned; or
d) Deviating from their original planned route (often direct routeing (DCT)).

In 35% of all reported ATFCM over-deliveries during 2008, the actual FL was different to the RFL in the Flight Plan.

Impact From an ATFCM Point of View

The network impact of the over-delivery can result in:

a) Wasted capacity in some sectors;
b) Potentially excessive workload;
c) An overall lack of confidence in the accuracy of forecast traffic counts. Accurate and reliable flight plan data is an essential prerequisite for correct sector counts, i.e. to protect ATC from overloads;
d) Protective capacity reduction;
e) Increased workload, stress or working conditions such that the ability of ATC controller to handle the traffic may be significantly impaired and thus a safety issue.

Support Requested

ANSPs, airport and aircraft operators are invited to respond to the following questions:

  1. How does non-adherence of EOBT/CTOT, requested level, or change of routeings affect your operations?
  2. What are the possible reasons (root causes) of non-adherence?
  3. What are your recommendations or proposed solutions to improve adherence and avoid re-occurrence?

Summary of Responses

How does non-adherence to EOBT/CTOT, requested level, or change of routings affect your operations?

Impact on AO

Non-adherence of EOBT/CTOT means downgrading of service level of the airline and non-efficient utilisation of its aircraft fleet. Non-adherence to CTOT has negative impact on operations, as it is always a delay. Getting the flight off-blocks earlier is considered an advantage, but gain is not more than 5 or 10 minutes. However, the advantage is imaginary in case of saturation or over-delivery at the airport of destination in which case flights are instructed to hold.

Flying at requested FL is always a benefit, because of lower fuel consumption and emissions.

Change of routing is sometimes due to saturation and in this case the new route is longer, therefore it has negative effect. Direct route clearance by ATC (granted very often) in real-time is an advantage, as it reduces fuel consumption.

Impact on ANSP

In general, non-adherence increases controller workload and is therefore considered a safety concern. The potential risk is always that of "ATCOs excessive workload" and any event derived from it. Capacity is wasted in some sectors while other sectors are overloaded. Granted direct routings may improve individual flight efficiency and contribute to reduced workload in own sector, however often have negative impact on adjacent sectors or ACCs. From a business point of view, the reduction of capacity far outweighs the ad-hoc improvements at individual flight level. Some ATS providers estimate that approximately 5-10% of capacity is 'reserved' to take care of all non-adherence issues, such as the tactical FL/route changes, as well as EOBT/CTOT non-adherence. The impact of non-adherence is believed to be lower in airspaces with low to medium traffic complexity.


What are the possible reasons (root causes) of non-adherence?

Most common reasons are commercial pressure, fuel saving and earlier/delayed off-block. For AOs on-time performance and fuel burn minimisation are second only to safety.

EOBT/CTOT non-adherence can be caused by:

  • Unrealistic turnaround times which put a strong pressure on pilots to depart even outside the CTOT to save a huge amount of delay as the new EOBT/CTOT will be much worse.
  • Delayed off-bock that can happen for several reasons: late passengers; inadequate number of airport security personnel; reactionary delay, unplanned maintenance work short time before departure and in very few cases due to lack of flight or cabin crew members (e.g. late show, maintenance).
  • Challenges with ground operations/turnover process at the airport (e.g. congestion)
  • Weather related problems, de-icing
  • Operational constraints (runway unavailability/changes, works, airspace closure, etc)
  • AO failure to update the EOBT compounded by ATC failure to manage both the operators and the CTOT compliance.
  • Inadequate coordination and ATC overload, sometimes by late planned charters.
  • Flawed actions by FMPs and flight dispatchers
  • At saturated airports CTOT compliance may come second in priority to making full use of available capacity and ensuring the needed runway throughput.
  • Underestimation of the network effects by ATC due to: low traffic levels at own airport; doubts about the credibility of traffic load figures; limited knowledge of the network and potential effects; wrong expectations on aircraft ability to make up for a delay
  • Misunderstanding of tactical loads and inadequate requests by FMPs for application of traffic exemption measures; and inadequate or frequently changed taxi times
  • Use of incorrect data in traffic prediction tools resulting in inadequate ATFM measures (for example filing duplicate or very similar FPLs distorts the traffic load figures calculated by FMPs) and reduced confidence in such tools.

Non-adherence of EOBT/CTOT has usually no negative consequences for the operational staff.

RFL & route non-adherence can be caused by:

  • Use of RPLs to generate CPL, the former being of limited accuracy by nature;
  • Pressure to fly the optimum profile for actual aircraft take-off mass rather than the assumed weight used to determine the RPL cruise level;
  • Pressure to reduce flight time due to late departure - pilots often fly faster and ask for shortcuts, and ATCOs often grant these.
  • Difference between statistical/estimated and actual winds;
  • Detailed differences between aircraft type variant performance versus the variant used to determine RPL cruise level
  • The operation of a particular flight under an RPL/FPL where an aircraft type change has not been amended.
  • Weather (turbulence) avoidance
  • Passenger comfort considerations including CAT and (for short haul) layer cloud tops avoidance;
  • There is no obligation for the pilots to adhere to the filed FL.
  • Direct clearances issued by ATC to ensure separation and expeditious traffic flow in TMAs or through own en-route sectors
  • Controllers being usually unaware which flights are subject to ATFM measures.
  • Disbelief among operational staff that flight planning tools of today can predict the most optimum flight profile within the known constraints.
  • Lack of understanding among the operational staff for the network effect of ones actions and decisions.
  • Deliberately filing of a routing/FL to obtain better slot-time and later requesting a change
  • Filing for a non-restricted airport with a restricted one as an alternative, then requesting to land at alternate when en-route.


What are your recommendations or proposed solutions to improve adherence and avoid re-occurrence?

Possible prevention solutions include:

  • Move away from RPLs and introduce a new system that will provide better optimal profiling.
  • Enable filing of direct routes for all aircraft operations - routes should be gradually redesigned according to AOs preferences. Once that is done, strictly adhere to FPL routings, levels and cruise speeds unless there is an aircraft safety issue (e.g. severe airframe icing, turbulence, weather).
  • ATFM should be improved starting from the time of RPL submission; improved HW & SW will ensure improved prediction and tracking of flights from take-off to destination, including on direct route segments.
  • Problems causing delayed off-block should be solved. It won’t be an easy task due to the production pressure on ANSPs, aircraft and airport operators.
  • Flight dispatchers should update the EOBT of the AFP based on the standing rules. Pilots should be informed of any FPL change and receive updated FPLs (AFP is corresponding to OFP). In case of ad-hoc rerouting pilots should get updated documents via ACARS.
  • Make it a requirement that all flight crew requesting a deviation give adequate descriptions of the actual or anticipated weather circumstances which have led to their request, especially in the case of CAT or layer cloud tops turbulence
  • Ensure that all ACCs can display (and adjust) weather returns on their radar screen when appropriate so that the potential impact of significant convective build ups can be taken into account proactively before the requests for deviation start coming in.
  • Ensure that ATC & cockpit systems identify a level capped flight to both crews and ATC.
  • Improve sector overload prediction and make this information available to individual controllers to prevent diverging aircraft from planned flight path.
  • Improve and make ATFCM training compulsory for TWR and AOs personnel concerned
  • Raise the awareness of involved ATC and AOs’ staff about the consequences: the extra workload due to over-delivery, in-flight holding and possible safety issues created by late changes to EOBT/FL/routing. Ops management should clearly communicate to concerned staff that non-adherence is not acceptable and promote strict adherence to the CTOT and filed FL/route.
  • Reduce corporate pressure on flight dispatchers and flight crews.
  • Controllers should initiate a change in the planned FL/routing level only in order to ensure safe separation, respectively pilots of flights subject to ATFM measures should request change of FL/routing only in case it is necessary for the safety of flight.
  • AOs that abuse the ATFM system should be penalized.
  • Adopt a European regulation to deter inappropriate practices of non-adherence.

Possible mitigation solutions include:

  • Improved planning and supervision of operations by ATC management in coordination with CFMU.
  • Revision of inadequate sector design, not capturing all aircraft;
  • Monitoring of declared sector capacity adequacy; improved tools for sector workload analysis and monitoring; reduced count interval (e.g. 10 min); CDM in case of extended period of over-delivery;
  • FSA/CPR transmission by all States and introduction of a CFMU message, such as SAM to regulate EOBT compliance.
  • Enhanced tactical ATC re-routing and timely coordination with adjacent sectors/centres; use of flight level allocation schemes (defined in LoAs) over the entry/exit FIR points.
  • Improved teamwork and management of real time traffic load balance between sectors.

Detailed responses

Disclaimer

© European Organisation for Safety of Air Navigation (EUROCONTROL) May 2009. This alert is published by EUROCONTROL for information purposes. It may be copied in whole or in part, provided that EUROCONTROL is mentioned as the source and to the extent justified by the non-commercial use (not for sale). The information in this document may not be modified without prior written permission from EUROCONTROL. The use of the document is at the user’s sole risk and responsibility. EUROCONTROL expressly disclaim any and all warranties with respect to any content within the alert, express or implied.