54TH ANNUAL CONFERENCE, Sofia, Bulgaria, 20-24 April 2015
WP No. 92
Responsibility For Terrain And Obstacle Clearance During Weather Avoidance
Presented by TOC
There is ambiguity over where the responsibility lies for provision of separation with terrain and obstacles. This was raised in a working paper at Conference 2013 and then studied in a working paper at Conference 2014. That working paper did not cover the case of weather deviations but recommended that a further study on that subject be done.
1.1 Responsibility for prevention of collisions with terrain is addressed in a number of ICAO PANS and SARPs but is only mentioned briefly. The guidance that is in those documents is open to interpretation and creates uncertainty about where that responsibility lies.
1.2 This uncertainty has been recognised for some time. It was raised in TOC papers at the IFATCA Annual Conference in 1994, 2007 and 2013. There are recent examples of controllers being prosecuted in courts of law for IFR aircraft under their control crashing into terrain.
1.3 At Conference in 2014 TOC presented Working Paper 85 Terrain and Obstacle Clearance Responsibilities. This paper made recommendations for clarifying responsibility for terrain and obstacle clearance.
1.4 WP85 also found that the topic of deviations from ATS routes due to severe weather required further study, and TOC was tasked with the subject for this year.
2.1 Normally when an aircraft is being vectored or given a more direct routing it is for separation or traffic management reasons. A controller will decide that it is safe and expeditious to do so. They will be in a position to decide whether they have the tools and can accept the workload of monitoring the navigation and separation from terrain of that aircraft. In this situation, it is not unreasonable that the responsibility for provision of terrain and obstacle clearance is assumed by the controller. If the controller is not in a position to accept that responsibility they have the option of leaving the aircraft on published procedures.
2.2 In the case of an aircraft requesting an off track deviation due to weather the situation is different. It is driven by the needs of the pilot rather than the controller. The direction and range of the deviation may be totally out of the hands of the controller. It may come when they are busy with other traffic or when the aircraft is below Minimum Vectoring Altitude (MVA), or even outside surveillance cover. The pilot may choose to fly a heading or may constantly adjust the aircraft track in a less defined manner to skirt the weather. Should the controller be made responsible for terrain and obstacle clearance when they cannot dictate the terms of the deviation?
2.3 ICAO References
2.3.1 There is little in ICAO Documents defining who is responsible for terrain and obstacle clearance. Existing references are contradictory, or do not reflect the modern ATM environment, with direct tracking, vectoring and RNP procedures regularly taking aircraft off published ATS Routes.
2.3.2 The Objectives of Air Traffic Control as defined in ICAO Annex 11 do not include prevention of collisions with terrain and obstacles, but at certain times, responsibility for provision of terrain and obstacle clearance is transferred to ATC, for example when the aircraft is being radar vectored.
ICAO Doc 4444 PANS ATM
22.214.171.124 When vectoring an IFR flight and when giving an IFR flight a direct routing which takes the aircraft off an ATS route, the controller shall issue clearances such that the prescribed obstacle clearance will exist at all times until the aircraft reaches the point where the pilot will resume own navigation.
2.4 Approved vs Cleared
2.4.1 Should ATC be responsible for providing terrain clearance when an off track deviation is being decided by the pilot rather than the controller?
2.4.2 One issue raised by weather deviations is whether approving a pilot request for deviation is the same as clearing an aircraft to deviate? More specifically, is approving a deviation the same as “giving an IFR flight a direct routing which takes the aircraft off an ATS route” from the passage above.
2.4.3 Approved is not defined in ICAO or IFATCA documents. The Oxford Concise English Dictionary defines approve as “officially agree to” which does not really answer our question.
2.4.4 In other instances in ATC where we use approved (eg: level change requests) the controller still remains responsible for ensuring the requested action is safe and fulfills the requirements of a clearance.
2.4.5 Alternatively, by specifying the course or direction of the deviation the pilot could be considered to be under his own navigation, and thereby responsible for his own obstacle clearance in accordance with PANS ATM 126.96.36.199.
2.4.6 TOC believes that approving a weather deviation off an ATS route could be interpreted as equivalent to “giving” one, and that by saying approved, controllers may be found to be accepting responsibility for terrain and obstacle clearance, according to the text currently in PANS ATM 188.8.131.52.
2.5 Clear of weather
2.5.1 If controllers are indeed responsible for providing terrain clearance while an aircraft deviates around weather, the point at which the responsibility transfers back to the pilot must be clearly defined.
2.5.2 If the aircraft is under vectors the controller has some degree of control over tracking but in other cases the weather deviation could end when the aircraft is outside controlled airspace, below MVA or outside surveillance coverage. It may be difficult for a controller to provide a safe clearance for the aircraft to resume normal flight.
2.5.3 The transfer of responsibility for terrain separation back to the pilot could be interpreted to be when “…the aircraft reaches the point where the pilot will resume own navigation”. But the weather deviation could position the aircraft well clear of the original route and a clearance for the pilot to track own navigation direct to a point may still leave ATC responsible, according to the text “…giving an IFR flight a direct routing which takes the aircraft off an ATS route”.
2.6 Chapter 15
2.6.1 Procedures for weather deviations in oceanic airspace are laid down in ICAO PANS ATM, in Chapter 15 entitled “Procedures related to emergencies, communication failure and contingencies”.
2.6.2 The text makes it clear that weather deviations can be a serious occurrence and advises pilots to call “PAN PAN” if necessary. It also advises them on what actions to take if ATC clearance cannot be obtained, including deviating without clearance if necessary.
184.108.40.206 ACTIONS TO BE TAKEN WHEN CONTROLLER-PILOT COMMUNICATIONS ARE ESTABLISHED
220.127.116.11.1 The pilot should notify ATC and request clearance to deviate from track, advising, when possible, the extent of the deviation expected.
18.104.22.168.2 ATC should take one of the following actions:
a) when appropriate separation can be applied, issue clearance to deviate from track; or
b) if there is conflicting traffic and ATC is unable to establish appropriate separation, ATC shall:
1) advise the pilot of inability to issue clearance for the requested deviation;
2) advise the pilot of conflicting traffic; and
3) request the pilot’s intentions.
22.214.171.124.3 The pilot should take the following actions:
a) comply with the ATC clearance issued; or
b) advise ATC of intentions and execute the procedures detailed in 126.96.36.199.
2.6.3 Unfortunately these procedures only specify actions to be taken when separation with conflicting traffic cannot be provided. There is no procedure for situations when controllers need to withhold clearance because they are unable to establish appropriate separation with terrain.
2.6.4 Because terrain is not mentioned, does this mean that ATC is not responsible for providing terrain clearance in this instance? That would be a very large assumption to make.
2.6.5 The procedure at 188.8.131.52.2 b) should be amended to include situations in any type of airspace when ATC cannot give clearance for a deviation as they are unable to provide separation with terrain.
2.6.6 This change would not have the effect of making ATC responsible for terrain separation during weather deviations, but would make clear how to proceed in any situation where ATC is responsible.
2.6.7 Any change must be aligned with clear and unambiguous procedures in Doc 4444, Doc 8168 and in other ICAO documentation.
184.108.40.206 ACTIONS TO BE TAKEN IF A REVISED ATC CLEARANCE CANNOT BE OBTAINED
Note.— The provisions of this section apply to situations where a pilot needs to exercise the authority of a pilot-in-command under the provisions of Annex 2, 2.3.1.
If the aircraft is required to deviate from track to avoid adverse meteorological conditions and prior clearance cannot be obtained, an ATC clearance shall be obtained at the earliest possible time. Until an ATC clearance is received, the pilot shall take the following actions:
a) if possible, deviate away from an organized track or route system;
b) establish communications with and alert nearby aircraft by broadcasting, at suitable intervals: aircraft identification, flight level, position (including ATS route designator or the track code) and intentions, on the frequency in use and on 121.5 MHz (or, as a backup, on the inter-pilot air-to-air frequency 123.45 MHz);
c) watch for conflicting traffic both visually and by reference to ACAS (if equipped);
Note.— If, as a result of actions taken under the provisions of 220.127.116.11.1 b) and c), the pilot determines that there is another aircraft at or near the same flight level with which a conflict may occur, then the pilot is expected to adjust the path of the aircraft, as necessary, to avoid conflict.
d) turn on all aircraft exterior lights (commensurate with appropriate operating limitations);
e) for deviations of less than 19 km (10 NM) remain at a level assigned by ATC;
f) for deviations greater than 19 km (10 NM), when the aircraft is approximately 19 km (10 NM) from track, initiate a level change in accordance with Table 15-1;
g) when returning to track, be at its assigned flight level when the aircraft is within approximately 19 km (10 NM) of the centre line; and
h) if contact was not established prior to deviating, continue to attempt to contact ATC to obtain a clearance. If contact was established, continue to keep ATC advised of intentions and obtain essential traffic information.
2.6.8 The “Actions to be taken if a revised ATC clearance cannot be obtained” detailed in 18.104.22.168 are not well suited to dealing with terrain and would likely need to be adapted. In some circumstances the procedures instruct the pilot to descend off track, in case of the presence of other aircraft.
2.7 ATC Duty of care
2.7.1 Duty of care is a legal term, which can be loosely defined as an obligation to take all reasonable steps to safeguard those in our care or receiving our service from harm.
2.7.2 Controllers have a duty of care to render any assistance they can to an aircraft in an emergency situation.
2.7.3 This presents a dilemma. Pilots are accustomed to taking instructions from controllers and may not recognize the difference between instructions and advice, or may be reluctant to act contrary to that advice.
2.7.5 Even after warning a pilot that there is no terrain separation, by giving advice, the controller may still assume a degree of responsibility for suggesting a course of action, which may prove to be unsafe.
2.7.6 If controllers do not have the tools to provide separation from terrain, the procedures should allow them to give any information and assistance that they can, without fear of being held responsible for an incident which they had no way of preventing.
2.8 No Clearance
2.8.1 If an aircraft does deviate off track, without gaining ATC clearance, is the pilot then responsible for separation with terrain? It seems self evident that a pilot who no longer remains within the terms of his clearance assumes all the responsibility, but in other instances this is specifically stated.
2.8.2 The procedure for carrying out a weather deviation without ATC clearance in Chapter 15 states that the pilot is expected to avoid conflicting traffic. It is clear where the responsibility for traffic avoidance lies, but not for terrain.
If, as a result of actions taken under the provisions of 22.214.171.124.1 b) and c), the pilot determines that there is another aircraft at or near the same flight level with which a conflict may occur, then the pilot is expected to adjust the path of the aircraft, as necessary, to avoid conflict.
2.8.3 In a similar case, the procedures for TCAS deviation specifically state that the controller ceases to be responsible for providing separation between the aircraft that has departed from its clearance and any other aircraft affected.
2.8.4 At the 2014 IFATCA annual conference in Gran Canaria the following policy was adopted:
|Responsibility for terrain and obstruction clearance must be clearly defined and always must lie either with the air crew or ATC. There must never be a situation where doubt exists about who is responsible for this task.|
2.8.5 This policy is valid. Chapter 15 already deals with weather deviations and could be modified to cover where the responsibility for terrain lies.
2.9 Non-Surveillance Airspace
2.9.1 In 2005 ICAO amended the PANS ATM 126.96.36.199 to add the words “and when giving an IFR flight a direct routing which takes the aircraft off an ATS route…” and removed the word “radar…” from in front of controller. Prior to that the passage had only discussed radar vectors. Unfortunately this amendment was not fully thought through and has raised further complications.
2.9.2 Chapter 8 in the PANS ATM, where this passage is located, is titled “ATS Surveillance Services” and is described as “containing procedures applicable by air traffic services units using radar in the performance of their functions”.
2.9.3 ATS Surveillance service is defined in ICAO Doc 4444 as:
“A term used to indicate a service provided directly by means of an ATS surveillance system”.
2.9.4 Considered on its own the passage 188.8.131.52 seems to state that anytime a controller gives a clearance off an ATS route they assume responsibility for terrain clearance. Should this be the case when the controller is providing a procedural control service? Or by placing the passage in Chapter 8 did ICAO intend that it should only apply to aircraft being provided with an ATS surveillance service?
2.9.5 Elsewhere, ICAO Doc 8168 PANS OPS specifically states that the pilot is responsible for obstacle clearance, except when the aircraft is being provided with radar vectors.
4.1.1 Pilot’s responsibility
The pilot-in-command is responsible for the safety of the operation and the safety of the aeroplane and of all persons on board during flight time (Annex 6, 4.5.1). This includes responsibility for obstacle clearance, except when an IFR flight is being vectored by radar.
2.9.6 The uncertainty created by the 2005 amendment to the PANS ATM does not appear to have been anticipated. The wording is now neither clear nor explicit and contradicts wording in other areas of ICAO Documents.
2.10 Objectives of ATS
2.10.1 The “Terrain and Obstacle Clearance Responsibilities” working paper last year resulted in IFATCA policy:
|ICAO documentation should provide clear and unambiguous language with regard to responsibility for terrain avoidance, including amendment to the Objectives of air traffic services to include the prevention of collisions between aircraft and terrain.|
2.10.2 ATS is defined in ICAO Doc 4444 as:
“A generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).”
2.10.3 It includes not only controllers but also other participants including charting, aeronautical information management, safety nets and many other areas.
2.10.4 By including prevention of collisions between aircraft and terrain in the objectives of Air Traffic Services IFATCA hopes to enable the necessary tools and information to be given to the people who require them. This is not the same as saying that controllers are always responsible for doing this task.
2.10.5 It is hoped that both controllers and aircrew will be provided with the tools to allow aircraft to safely fly off the traditional route structure when deemed necessary. This IFATCA policy is still valid.
3.1 Controllers should be aware of the implications of saying “Approved” in any situation as it may be interpreted to be the equivalent of saying “Cleared”.
3.2 With due regard to the requirements of “Duty of Care”, controllers should not approve or clear aircraft to carry out weather deviations that are not separated from terrain and obstacles until the ambiguities over where the responsibility lies are resolved. The pilot should be informed of the reason why so that they may exercise their authority to proceed with the deviation if deemed necessary.
3.3 The procedure in PANS ATM Chapter 15 184.108.40.206 “ACTIONS TO BE TAKEN WHEN CONTROLLER-PILOT COMMUNICATIONS ARE ESTABLISHED” should include situations in any airspace where an ATC clearance cannot be given due to terrain. This will make clear to pilots and controllers who is responsible for separation with terrain in that situation, and how to act.
3.4 The procedure in PANS ATM Chapter 15 220.127.116.11 “ACTIONS TO BE TAKEN IF A REVISED ATC CLEARANCE CANNOT BE OBTAINED” should be amended to make clear that the pilot is responsible for avoiding terrain when deviating without clearance. This will allow pilots to deviate without clearance if they are satisfied that it is safer to do so.
3.5 If controllers do not have the tools to provide separation from terrain, the procedures should allow them to give any information and assistance that they can, without fear of being held responsible for an incident which they had no way of preventing. Implementation of improved tools and procedures would allow controllers to provide greater assistance to pilots, and more efficient separation with terrain, when required.
3.6 PANS ATM 18.104.22.168 should be amended to clarify when responsibility for separation with terrain changes between the pilot and the controller. It should be clear that only controllers utilising ATS surveillance systems for provision of an ATC service can accept this responsibility.
3.7 Any changes to ICAO documents regarding responsibility for separation from obstacles and terrain should be aligned with procedures and guidance in other areas of ICAO documents to avoid conflicting statements.
4.1 IFATCA Policy is:
Development of ATS surveillance tools and procedures to allow ATCOs to accurately and efficiently separate from terrain is encouraged.
4.2 It is recommended that:
IFATCA introduce a paper to the ICAO ATMOPS Panel to have paragraphs 22.214.171.124 and 126.96.36.199 of Doc 4444 adapted for all airspace, and amended to include terrain and restricted airspace.
4.3 It is recommended that:
IFATCA introduce a paper to the ICAO ATMOPS Panel to have paragraph 188.8.131.52 amended to remove ambiguity regarding responsibility for provision of separation with obstacles and terrain.
ICAO Annex 2.
ICAO Doc 4444 PANS ATM.
ICAO Doc 8168 PANS OPS.
IFATCA 2014 WP 85 Terrain and Obstacle Clearance Responsibilities.
IFATCA 2013 WP 89 Terrain Clearance and Airspace Design.
IFATCA 2007 WP 92 Surveillance Applications Policy – Review Policy on Radar Monitoring.
IFATCA 1994 WP 101 Radar Monitoring Procedures in TMA’s.
IFATCA Technical and Professional Manual 2014.
Last Update: October 1, 2020