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Oceanic Loss of RVSM Capability

Abnormal Procedures

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

[ICAO Doc 9574, ¶5.1.1 h)] the following contingency procedures should be adhered to after entering RVSM airspace:

  1. 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;
  2. 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;
  3. the pilot should notify ATC when encountering severe turbulence; and
  4. if unable to notify ATC and obtain an ATC clearance prior to deviating from the assigned CFL, the pilot should follow established contingency procedures as defined by the region of operation and obtain ATC clearance as soon as possible.

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.

Initial Action

[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.

Subsequent Action

[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:

  1. climb or descend 1000 ft if above FL410
  2. climb or descend 500 ft when below FL410
  3. 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

The basic general procedures are outlined below. Consult AIPs, Jeppesen State Pages, and ICAO Document 7030, Regional Supplementary Procedures, for regional differences. [AC 91-85, Appendix 5]

  • 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]

Example Scenarios

Appendix 5 of AC 91-85 Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum Airspace provides several scenarios to summarize pilot actions to mitigate the potential for conflict with other aircraft in certain contingency situations.

Scenario 1 — "Unsure"

[AC 91-85, Appendix 5, ¶5.b.(1)]

The pilot is: 1) unsure of the vertical position of the aircraft due to the loss or degradation of all primary altimetry systems, or 2) unsure of the capability to maintain CFL due to turbulence or loss of all automatic altitude control systems.

  • Maintain CFL while evaluating the situation;
  • Watch for conflicting traffic both visually and by ACAS;
  • If considered necessary, alert nearby aircraft by:
    1. Making maximum use of exterior lights;
    2. Broadcasting position, FL, and intentions on 121.5 MHz (as a back-up, the VHF inter-pilot air-to-air frequency may be used).
  • Notify ATC of the situation and intended course of action. Possible courses of action include:
    • Maintaining the CFL and route provided that ATC can provide lateral, longitudinal or conventional vertical separation.
    • Requesting ATC clearance to climb above or descend below RVSM airspace if the aircraft cannot maintain CFL and ATC cannot establish adequate separation from other aircraft.
    • Executing the ICAO Doc. 4444 contingency maneuver to offset from the assigned track and FL, if ATC clearance cannot be obtained and the aircraft cannot maintain CFL.
    • The "Quad Four Maneuver" is so called because it is found in ICAO Doc. 4444.

      Details: Special Procedures for In-flight Contingencies in Oceanic Airspace.

Scenario 2 — Bad Altimeter

[AC 91-85, Appendix 5, ¶5.b.(2)]

There is a failure or loss of accuracy of one primary altimetry system (e.g., greater than 200 ft difference between primary altimeters).

The Pilot should cross check standby altimeter, confirm the accuracy of a primary altimeter system and notify ATC of the loss of redundancy. If unable to confirm primary altimeter system accuracy, follow pilot actions listed in the preceding scenario.

Scenario 3 — All Altitude Control Systems Fail

[AC 91-85, Appendix 5, ¶6.a.(1)]

If all automatic altitude control systems fail, the pilot should:

  • Maintain CFL while evaluating the situation;
  • Evaluate the aircraft's capability to maintain altitude through manual control;
  • Watch for conflicting traffic both visually and by ACAS;
  • If considered necessary, alert nearby aircraft by:
    1. Making maximum use of exterior lights;
    2. Broadcasting position, FL, and intentions on 121.5 MHz (as a back-up, the VHF inter-pilot air-to-air frequency may be used).
  • Notify ATC of the situation and intended course of action. Possible courses of action include:
    • Maintaining the CFL and route provided that ATC can provide lateral, longitudinal or conventional vertical separation.
    • Requesting ATC clearance to climb above or descend below RVSM airspace if the aircraft cannot maintain CFL and ATC cannot establish adequate separation from other aircraft.
    • Executing the ICAO Doc. 4444 contingency maneuver to offset from the assigned track and FL, if ATC clearance cannot be obtained and the aircraft cannot maintain CFL.
    • The "Quad Four Maneuver" is so called because it is found in ICAO Doc. 4444.

      Details: Special Procedures for In-flight Contingencies in Oceanic Airspace.

Scenario 4 — Loss of Redundancy in Primary Altimetry Systems

[AC 91-85, Appendix 5, ¶6.b.(2)]

There is a loss of accuracy in primary altimetry systems.

If the remaining altimetry system is functioning normally, the pilot should couple that system to the automatic altitude control system, notify ATC of the loss of redundancy and maintain vigilance of altitude keeping.

Scenario 5 — All Primary Altimetry Systems are Considered Unreliable or Fail

[AC 91-85, Appendix 5, ¶6.b.(3)]

If all primary altimetry systems fail, the pilot should:

  • Maintain CFL by reference to the standby altimeter;
  • Alert nearby aircraft by:
    1. Making maximum use of exterior lights;
    2. Broadcasting position, FL, and intentions on 121.5 MHz (as a back-up, the VHF inter-pilot air-to-air frequency may be used).
  • Consider declaring an emergency. Notify ATC of the situation and intended course of action. Possible courses of action include:
    • Maintaining CFL and route provided that ATC can provide lateral, longitudinal or conventional vertical separation.
    • Requesting ATC clearance to climb above or descend below RVSM airspace if the aircraft cannot maintain CFL and ATC cannot establish adequate separation from other aircraft.
    • Executing the ICAO Doc. 4444 contingency maneuver to offset from the assigned track and FL, if ATC clearance cannot be obtained and the aircraft cannot maintain CFL.
    • The "Quad Four Maneuver" is so called because it is found in ICAO Doc. 4444.

      Details: Special Procedures for In-flight Contingencies in Oceanic Airspace.

Scenario 6 — Divergence

[AC 91-85, Appendix 5, ¶6.d.]

If the primary altimeters diverge by more than 200 ft (60 m), the pilot should:

  • Attempt to determine the defective system through established trouble-shooting procedures and/or comparing the primary altimeter displace to the standby altimeter (as corrected by the correction cards, if required).
  • If the defective system can be determined, couple the functioning altimeter system to the altitude keeping device.
  • If the defective system cannot be determined, follow the guidance in Scenario 5 for failure or unreliable altimeter indications of all primary altimeters.

Scenario 7 — Turbulence

[AC 91-85, Appendix 5, ¶6.e.]

In the event of turbulence (greater than moderate) which the pilot believes will impact the aircraft’s capability to maintain FL, the pilot should:

  • Watch for conflicting traffic both visually and by ACAS;
  • If considered necessary, alert nearby aircraft by:
    1. Making maximum use of exterior lights;
    2. Broadcasting position, FL, and intentions on 121.5 MHz (as a back-up, the VHF inter-pilot air-to-air frequency may be used).
  • Notify ATC of the situation and intended course of action. Possible courses of action include:
    • Maintaining the CFL and route provided that ATC can provide lateral, longitudinal or conventional vertical separation.
    • Requesting ATC clearance to climb above or descend below RVSM airspace if the aircraft cannot maintain CFL and ATC cannot establish adequate separation from other aircraft.
    • Executing the ICAO Doc. 4444 contingency maneuver to offset from the assigned track and FL, if ATC clearance cannot be obtained and the aircraft cannot maintain CFL.
    • The "Quad Four Maneuver" is so called because it is found in ICAO Doc. 4444.

      Details: Special Procedures for In-flight Contingencies in Oceanic Airspace.

Book Notes

Portions of this page can be found in the book International Flight Operations, Part VI, Chapter 4.

References

Advisory Circular 91-85, Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum Airspace, 8/21/09, 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 2017-1

Revision: 20170505
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