54TH ANNUAL CONFERENCE, Sofia, Bulgaria, 20-24 April 2015
WP No. 83
Flight Planning Impacts on the ATM System
Presented by TOC
Inaccuracies during initial flight planning or insufficient communication regarding changes to existing flight plans can lead to undesirable effects on the ATM system. This paper discusses the most common issues currently experienced with flight planning.
1.1 In order to facilitate the safe and efficient flow of air traffic, accurate flight planning is essential. The flight plan contains crucial information about the crew’s intentions and the aircraft’s capabilities, and an accurate representation of those informs the ATM system in general and the controller in particular about current and future traffic demands, restrictions and abilities.
1.2 The variation in capabilities between ATS units, demands between different sectors or airspaces and individual capabilities of aircraft, leads to a high diversity and complexity when it comes to correctly completing and filing a flight plan. It is not unusual for flight plans to be incompletely or incorrectly filed.
1.3 As there are large differences in local requirements to flight plans worldwide and even from flight to flight, and in the capabilities of ATS units for the exchange of flight data, we will be looking mostly at the basic means with which we can ensure accurate filing of flight plans.
2.1 The flight planning process
2.1.1 Flight plans must be filed for all flights crossing international borders and for most other flights that are operated commercially. ICAO provides a model flight plan form and extensive regulations for the completion of a flight plan in DOC 4444. All flight plans filed shall be submitted using a form based on the model in Appendix 2, provided by the ATS unit. Flight plans shall be completed using the international and national standards and restrictions as defined by ICAO and the local Aeronautical Information Publications.
2.1.2 After the flight plan is submitted the ATS unit which received it will check it for inaccuracies or inconsistencies. The operator or crew shall be informed of the plan’s acceptance or rejection. After acceptance the receiving ATS unit will forward the flight plan to all other ATS units concerned. Any changes to the flight plan shall be communicated to the relevant ATS unit(s).
2.1.3 ANSPs have varying capabilities with regards to flight plan conformance checking. Automated systems may have the capability to compare filed flight plans with local flight planning regulations, and reject or propose amendments accordingly.
2.1.4 Advanced systems can compare information provided in flight plans with aircraft equipage and performance databases and alert either the operator, ATCO or Flight Data Officer to potential discrepancies, allowing early intervention to correct potential errors.
2.1.5 In many cases, conformance checking is limited to manual assessment by flight data or briefing staff, which relies heavily on human resourcing and appropriate training to ensure flight planning accuracy.
2.2 Common flight planning issues and consequences
2.2.1 A common and recurring issue is the difference between flight planned speed and flown speed. Airlines generally plan a generic speed for a fleet type, however it is common for flight crew to vary the speed in flight without informing ATC due to operational circumstances. Variances in flight planned and actual speed can have the following effects on the ATM system:
- Incorrect forward calculation of estimates – particularly in Oceanic and remote airspace;
- Instability in calculation of arrival sequences, particularly with automated sequencing software that draws speed information from what has been filed rather than derives it from surveillance data.
A pending change to ICAO Annex 2 proposes pilots will be required to report a variation of speed by more than 10 knots to ATC, rather than the 5% of speed it is now. This would of course go great lengths to reducing the impact of this issue.
2.2.2 Incorrect planning of RVSM or Negative RVSM status remains an issue in non-exclusive airspace. Planning RVSM approval when not approved can lead to loss of separation, or conversely, planning negative RVSM when approved can lead to an aircraft being assigned reduced priority for level assignment, or sub-optimal levels.
2.2.3 A late aircraft change often leads to incorrect registration data in the flight plan. CPDLC connections are contingent on correlation with the flight planned registration, and registration and other data in a logon request from the aircraft. Incorrect flight plan registration data can lead to prolonged periods of no communication in remote and oceanic airspace.
2.2.4 Incorrect data can pose serious risks if an incident occurs during flight as fire brigades and search and rescue operations rely on information from the flight plan to make decisions during a crisis situation.
2.2.5 When the flight plan form is not correctly filled in and the flight plan consequently rejected, dispatchers sometimes work around this by omitting parts of equipage, in order to get the flight plan accepted. This may lead to expectations in the cockpit differing to expectations on the ground.
2.2.6 Sometimes, no flight plan is filed at all or it’s not communicated to adjacent units. Consequences may include, but are not limited to:
- Loss of separation.
- Increased controller workload.
- Incorrect boundary estimates.
- Inaccurate coordination between ATS units.
2.2.7 In other cases, a flight plan has been filed, but the dissemination is inadequate or inaccurate, or there is a system error which prevents the flight details from being presented to ATC.
2.2.8 In both of the above events, controller and flight deck workload are significantly increased because of the need to file a flight plan while airborne. This is a common occurrence in airspaces where systems are outdated or the threshold for filing a flight plan is relatively high (i.e. only on paper at a flight information office).
2.2.9 If the rejection of a flight plan is not communicated to the flight crew, controller workload may be significantly increased due to inquiries from the crew. Sometimes the issue can be resolved easily with a minor change made by local troubleshooters. Other times controllers may need to create a flight plan using the information provided by pilots. This can be a large drain on frequency time and mental resources.
2.2.10 Even if a briefing officer is present to take care of the flight plan, there is a lot of pressure to file the plan quickly in these cases. This leads to a higher error rate because of less thorough checking of the entered data.
2.2.11 A contributing factor to flight plans not being filed can be the barrier of entry to the flight planning systems. In some areas, flight plans can only be submitted by paper. A flight plan processing unit that is available online or via phone lines could assist in preventing lack of correct planning.
2.2.12 Robust and reliable links along which to send flight plan data are not always present between ANSPs. System limitation, political conflict or inadequate resources may all contribute to the failure of data being passed correctly.
2.3 Flight planning through third parties
2.3.1 Corporate aviation and charter operators often makes use of third parties to file their flight plans. These companies provide pilots with applications that allow them to submit their flight plans easily. For example, in Europe, the user is only required to enter the departure and arrival aerodrome. The application then sources several possible compliant routes from the Integrated Flight Plan System (IFPS), which it presents to the user. They then pick the desired route and submit it directly via AFTN. Acceptance or rejection is usually instantaneous.
2.3.2 Problems arise when the flight plan is not immediately accepted or rejected by IFPS. The user may be under the impression that the flight plan has been filed but it may get rejected later after review by the receiving unit(s). Because the flight plan was submitted through a third party which operates their office only during office hours, sometimes the originator cannot be reached to communicate a rejection. This may result in pilots being confronted with rejections in flight while they were working under the assumption that their flight plan had been accepted.
2.3.3 Training of dispatchers sometimes lags behind the addition of new routes or new definitions of airspace. This of course causes problems while filing plans as the filer is not fully aware of the requirements, restrictions or possibilities of a given route.
2.3.4 In some regions dispatchers are not up-to-date on the norms required for the correct filing of flight plans. This results in issues such as, but not limited to:
- Incorrect routing.
- Incorrect equipage.
- Incorrect information on RVSM capabilities.
- Shortcuts to simplify filing resulting in inaccuracies.
2.4 Flight planning and safety net alerts
2.4.1 Flight planning inaccuracy can lead to the alerting service of ATS units being compromised, because it is contingent on several key points included in flight plans. The filing and processing of flight plans should therefore be a high priority to the responsible parties. Whether they be dispatchers, air crews, operators, flight planning offices or ANSPs.
2.4.2 In some regions, ANSPs are moving towards (or have already implemented) automated conflict detection. In such cases the system is legally and operationally responsible for detection of conflicts, not the controller. Correct information is even more crucial in these systems because if the information is incorrect, so is the system’s conclusion on conflict. This will be an important factor in the future as systems and tools that support controllers will rely more and more on accurate data to provide support.
2.4.3 In Europe flight plans are used to calculate airspace and aerodrome capacity and delays. That means that in order to expedite their flights, dispatchers often delete a flight plan and refile using a different route and/or level. The flight deck may not be aware of these last minute changes, and would then have different expectations of the flight profile than ATC. This can lead to unexpected turns or flights entering military airspace without proper coordination.
2.4.4 Airlines have also been known to make last minute route changes for security reasons. This can and has led to unexpected situations where controllers were confronted with aircraft flying different routes than expected.
2.4.5 Sometimes a new flight plan does not actually avoid a restriction further down the line, but it takes a given amount of time for flow control to award a flight a CTOT. It is therefore possible that the new flight plan slips through the cracks and generates a slot violation, leading to congestion.
2.5 Complexity of flight planning regulations
2.5.1 Especially for flights that cross several jurisdictions, flight planning can become very complex, due to differing flight planning requirements. Sometimes multiple documents need to be referenced in order to file a conforming flight plan.
2.5.2 For example, in Australia, different regions allow for different flight planning options. The manuals for these options can be confusing and difficult to read. The case of Australia is not an exception, as most regions have different demands as to the content of the flight plan. This is often a problem for incidental flights, where the flight planner does not have a routine knowledge of the airspaces involved.
2.6 Distribution of flight plans and changes among ANSPs
2.6.1 All ANSPs should receive border crossing flight plans from their neighbours. Changes to routing, level and speed are also supposed to be communicated according to ICAO regulations and applicable LoAs.
2.6.2 If messages are passed inaccurately, or not at all, adjacent units may find themselves with unexpected situations. Some providers reject messages from neighbours outright due to a high error rate in the messages sent, increasing system backlog and requiring manual checking and correction.
2.6.3 There are cases of ANSP suspending certain services regarding flight plans that pilots may not be aware of. For example, some ANSPs do not forward flight plans that concern flights departing from aerodromes outside their FIR. This can sometimes mean that the user assumes a correct filing, but relevant ATS units have not received the data.
2.7 Notable incident where flight planning was a contributing factor
2.7.1 On May 9th 2012 a Sukhoi Superjet 100 crashed into Mount Salak in Indonesia whilst on a demonstration flight. While there were many contributing factors to this accident, there were a number of issues regarding the planning of the flight.
2.7.2 The initial route planned by the ground handling operator was rejected by the briefing office at Halim Airport, due to the route interfering with traffic for Soekarno-Hatta International Airport. The briefing office suggested a new route which was accepted by ground handling staff, however the route passed on to the flight crew was incomplete. The captain would later make another amendment to the planned route.
2.7.3 Halim Tower overheard the briefing office staff mention that the first demonstration flight used a nearby military training area, the assumption was then made that the next flight would head there.
2.7.4 Due to the aircraft type not being available in the system, the aircraft type was incorrectly entered as a Sukhoi 30 military jet. When Halim Tower coordinated with Jakarta Approach, the tower controller mentioned that the flight was heading to a training area. This coordination, in conjunction with the incorrect information entered into the flight data system, led the approach controller to believe that the flight was performed using a military aircraft. It was only after surveillance and radio contact were lost that Approach realised it was a passenger jet.
2.7.5 The above illustrates a case in which many assumptions were made and shortcuts were taken regarding the planning of the flight and the correct entering of data into ATM systems. While not a direct cause of the flight crashing, a more accurate representation of intended flight path and type of flight may have raised questions during an earlier phase of the flight.
2.8 The future of flight plan data
2.8.1 ICAO is working on a replacement to the current ICAO flight plan. The working title for this project is Flight and Flow – Information for a Collaborative Environment (FF-ICE).
2.8.2 One of FF-ICE’s grounding principles is the sharing of information regarding the flight between flight deck, service providers and operators in order to increase safety and (perhaps even more so) efficiency.
2.8.3 Accuracy will become easier to achieve if information is continuously and consistently shared. On the other hand, systems will become ever more reliant on accurate data as their complexity and sophistication increases. Accurate information will only increase in importance in the future.
2.9 Methods of filing and automated conformance checking
2.9.1 There are a number of ways in which flight plans are submitted to ANSPs, these include but are not limited to:
- Direct from operators into AFTN.
- Via purpose-built websites or applications.
- At a briefing office, either via phone lines, fax or physically at the office using a paper form.
- On a dedicated frequency.
- On the frequency through a controller engaged in separating traffic.
2.9.2 The methods by which operators can submit flight plans directly to AFTN vary slightly from state to state. However, in general, these direct submissions are automatically checked for conformance and accepted or rejected without human intervention.
2.9.3 Some ANSPs have created purpose built websites that allow for direct submission of the flight plan. This allows the ANSP to check the flight plan for conformance and submit it to AFTN for further dissemination. If the website is well designed, errors can be prevented before they even occur.
2.9.4 Applications by third parties can be useful if careful agreements are set out with regards to responsibility for conformance checking. In this manner, errors in submitted flight plans can be prevented or corrected before submission to the ATM system.
2.9.5 Submissions that are reviewed and/or accepted by human officers are more error prone than the above as they rely on human resourcing and adequate training. On top of that, errors are more likely in high workload situations. It is therefore the opinion of TOC that it is preferable to submit flight plans through electronic means if practicable.
3.1 Incorrect and late filing, or total absence of flight plans have a significant detrimental effect on controller workload. ANSPs, regulators, operators and all other relevant stakeholders should make every effort to ensure flight plans are accurate and up-to- date in order to keep safety concerns to a minimum.
3.2 Accurate flight plans are critical for any future developments in ATC and ATM. Appropriate training is essential to guarantee dispatchers and briefing officers are current on the requirements and finer details of the flight plan.
3.3 Data and intentions must be accurate in order to provide safe and efficient ATS.
3.4 It should be as easy as possible to submit a complete and accurate flight plan for every flight. TOC believes that electronic means of submission are the way forward because they reduce workload for dispatchers, briefing officers and ATCOs. As we reduce this workload, we also reduce the likelihood of errors occurring in flight plans or the ATM system as a whole.
3.5 Responsibility for conformance checking, flight plan amendment or other troubleshooting should not lie with controllers for reasons of workload management. Electronic filing and automated conformance checking, including feedback on errors made by the submitter, would prevent this from happening.
4.1 It is recommended that IFATCA policy is:
Electronic filing and automated conformance checking of flight plans are preferable.
4.2 It is recommended that IFATCA policy is:
Interaction with flight plans should be minimised for controllers engaged in separating aircraft.
ICAO Annex 2 Rules of the Air.
ICAO Doc 4444 PANS-ATM.
Off Air Routes Planning Manual: http://www.airservicesaustralia.com/flight-briefing/off-air-route-flight-planning-options/flight-planning-regional-options, Airservices Australia, version 22, August 2014.
Aircraft Accident Investigation Report Sukhoi RRJ-95B: http://kemhubri.dephub.go.id/knkt/ntsc_aviation/baru/Final%20Report_97004_Release.pdf, Indonesian National Transport Safety Committee, 2012.
Last Update: October 1, 2020