Oceanic Loss of RVSM Capability
Losing your ability to keep the airplane precisely on altitude is becoming a bigger deal every day, as the skies are becoming more tightly packed. Because each situation is likely to be unique, there are no cut and dried rules that always apply.
- ICAO Contingency Procedures are given in ICAO Doc 9574 and are summarized here.
- North Atlantic Procedures are given in ICAO Nat Doc 001 and are summarized here.
- Other Regional Differences are given in ICAO Doc 7030 and are summarized here.
ICAO Contingency Procedures
[ICAO Doc 9574, ¶5.1.1 h)] the following contingency procedures should be adhered to after entering RVSM airspace:
- the pilot should notify ATC of contingencies (equipment failures, weather conditions) in which the ability to maintain CFL is affected and coordinate a plan of action;
- equipment failures should be notified to ATC. Some examples are:
- failure of all automatic altitude-keeping devices on board the aircraft;
- loss of redundancy of altimetry systems, or any part of these, on board the aircraft;
- failure of all altitude-reporting transponders;
- loss of thrust on an engine necessitating descent; and
- any other equipment failure affecting the ability to maintain CFL;
North Atlantic Procedures
[ICAO NAT Doc 007, ¶13.3.1] The general concept of these Oceanic in-flight contingency procedures is, whenever operationally feasible, to offset from the assigned route by 15 NM and climb or descend to a level which differs from those normally used by 500 ft if below FL410 or by 1000 ft if above FL410.
[ICAO NAT Doc 007, ¶13.3.2] The aircraft should leave its assigned route or track by initially turning at least 45° to the right or left whenever this is feasible. The direction of the turn should, where appropriate, be determined by the position of the aircraft relative to any organised route or track system (e.g. whether the aircraft is outside, at the edge of, or within the system). Other factors which may affect the direction of turn are: direction to an alternate airport, terrain clearance, levels allocated on adjacent routes or tracks and any known SLOP off sets adopted by other nearby traffic.
[ICAO NAT Doc 007, ¶13.3.3] An aircraft that is able to maintain its assigned flight level, after deviating 10 NM from its original cleared track centreline and therefore laterally clear of any potentially conflicting traffic above or below following the same track, should:
- climb or descend 1000 ft if above FL410
- climb or descend 500 ft when below FL410
- climb 1000 ft or descend 500 ft if at FL410
[ICAO NAT Doc 007, ¶13.3.4] An aircraft that is unable to maintain its assigned flight level (e.g due to power loss, pressurization problems, freezing fuel, etc.) should, whenever possible, initially minimise its rate of descent when leaving its original track centreline and then when expected to be clear of any possible traffic following the same track at lower levels and while subsequently maintaining a same direction 15 NM offset track, descend to an operationally feasible flight level, which differs from those normally used by 500 ft if below FL410 (or by 1000 ft if above FL410).
[ICAO NAT Doc 007, ¶13.3.5] Before commencing any diversion across the flow of adjacent traffic or before initiating any turn-back (180°), aircraft should, while subsequently maintaining a same direction 15 NM offset track, expedite climb above or descent below the vast majority of NAT traffic (i.e. to a level above FL410 or below FL280), and then maintain a flight level which differs from those normally used: by 1000 ft if above FL410, or by 500 ft if below FL410. However, if the pilot is unable or unwilling to carry out a major climb or descent, then any diversion or turn-back manoeuvre should be carried out at a level 500 ft different from those in use within the NAT HLA, until a new ATC clearance is obtained.
[ICAO NAT Doc 007, ¶13.3.6] If these contingency procedures are employed by a twin engine aircraft as a result of the shutdown of a power unit or the failure of a primary aircraft system the pilot should advise ATC as soon as practicable of the situation, reminding ATC of the type of aircraft involved and requesting expeditious handling.
Other Regional Differences
- Africa / Indian Ocean: standard contingency procedures [ICAO Document 7030, AFI, Paragraph 9.5]
- Caribbean: standard contingency procedures [ICAO Document 7030, CAR, Paragraph 9.5]
- Europe: If vertical navigation performance requirements cannot be maintained, pilots must obtain a revised ATC clearance prior to initiating and deviation from the cleared route and/or flight level, whenever possible. Pilots will inform ATC if severe turbulence impacts an aircraft's ability to maintain its cleared flight level, ATC will either establish horizontal separation or an increased vertical separation. [ICAO Document 7030, EUR, Paragraph 9.5]
- Middle East / Asia: Pilots will inform ATC if severe turbulence impacts an aircraft’s ability to maintain its cleared flight level, ATC will either establish horizontal separation or an increased vertical separation. [ICAO Document 7030, MID/ASIA, Paragraph 9.5]
- North America: standard contingency procedures [ICAO Document 7030, NAM, Paragraph 9.5]
- North Atlantic: standard contingency procedures [ICAO Document 7030, NAT, Paragraph 9.5] as well as the specific instructions given in ICAO Nat Doc 001, and summarized above.
- Pacific: standard contingency procedures [ICAO Document 7030, PAC, Paragraph 9.5]
- South America: standard contingency procedures [ICAO Document 7030, SAM, Paragraph 9.5]
Portions of this page can be found in the book International Flight Operations, Part VI, Chapter 4.
Advisory Circular 91-85B, Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum Airspace, 1/21/19, U.S. Department of Transportation
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, October 2016
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2008
ICAO Doc 9574 - Manual on Implementation of a 300 m (1,000 ft) Vertical Separation Minimum Between FL 290 and FL 410 Inclusive, Second Edition, International Civil Aviation Organization, 2001
ICAO NAT Doc 001, Guidance and Information Material Concerning Air Navigation in the North Atlantic Region, Seventh Edition, January 2002
ICAO NAT Doc 007, North Atlantic Operations and Airspace Manual, v 2018-1