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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

Contingencies Within MNPS Airspace

[ICAO Nat Doc 001, ¶3.10]

  • This guidance material should enable the pilot and the air traffic controller to better understand what actions to take under certain conditions of equipment failure and during encounters with turbulence. A pilot should notify ATC of any contingency that affects the ability of the aircraft to maintain the CFL (particularly in RVSM Airspace). Together they should coordinate a plan of action. Examples of notifiable equipment failures are:
    1. failure of all automatic AKDs [Altitude Keeping Devices] onboard the aircraft;
    2. full or partial loss of redundancy of altimetry systems aboard the aircraft;
    3. loss of thrust on an engine necessitating descent; or
    4. any other equipment failure affecting the ability to maintain CFL;
  • However, it is recognized that both a pilot and controller will use their judgement to determine the action most appropriate to any given situation. For certain equipment failures, the safest course of action may be for the aircraft to continue in MNPS Airspace while the pilot and controller take precautionary action to protect separation. For extreme cases of equipment failure, the safest course of action may be for the aircraft to leave MNPS Airspace after obtaining a revised ATC clearance. If unable to obtain such prior clearance then the pilot should execute a contingency manoeuvre and leave the assigned route or track, as specified in the ‘NAT’ Section, of the ICAO “Regional Supplementary Procedures” (Doc.7030).

Contingencies Within RVSM Airspace

[ICAO Nat Doc 001, ¶3.11]

  • The following guidance on contingency procedures to adopt when encountering loss of height keeping equipment, should not be interpreted in any way that prejudices the final authority and responsibility of the pilot-in-command for the safe operation of the aeroplane.
  • All Automatic Altitude Keeping Devices Fail

  • If all automatic AKDs fail (e.g. autopilot altitude hold) then the pilot should:
    1. maintain CFL - if necessary through manual control;
    2. watch for conflicting traffic;
    3. if applicable, alert nearby aircraft by:
      1. making maximum use of exterior lights; and
      2. broadcasting position, flight level, and immediate intentions, on frequency 121.5 MHz; and
    4. notify ATC of the failure and state the intended course of action. Possible courses of action include:
      1. continuing in RVSM Airspace provided that the aircraft can maintain the CFL; or
      2. requesting ATC clearance to climb above or descend below RVSM Airspace, if the aircraft cannot maintain the assigned flight level and ATC cannot establish increased vertical, longitudinal or lateral separation; or
      3. executing the appropriate contingency manoeuvre specified in ICAO Doc.7030 to leave the assigned route or track if prior ATC clearance cannot be obtained and the aircraft cannot maintain the assigned flight level.
  • ATC should take the following action: obtain the pilot's intentions;
    1. if the pilot intends to continue in RVSM Airspace, consider establishing increased vertical, longitudinal or lateral separation;
    2. pass traffic information to the pilot;
    3. if the pilot requests clearance to exit RVSM Airspace, accommodate that request as expeditiously as possible;
    4. if increased vertical, longitudinal or lateral separation cannot be established and it is not possible to comply with the pilot's request for clearance to exit MNPS Airspace, then to notify other aircraft in the vicinity and continue to monitor the situation; and
    5. advise adjacent ATC facilities/sectors, of the situation.

    Loss of Redundancy in the Primary Altimetry Systems

  • The pilot should take the following action, if the remaining altimetry system is functioning normally:
    1. couple that system to the AKD;
    2. notify ATC of the loss of redundancy; and
    3. maintain increased vigilance regarding altitude-keeping.
  • If the pilot reports that the remaining system is functioning normally the ATC controller should acknowledge the situation and continue to monitor progress.
  • All Primary Altimetry Systems Fail or are Considered Unreliable

  • The pilot should:
    1. maintain altitude - if necessary by reference to the standby altimeter (should the aircraft be so equipped);
    2. alert nearby aircraft by:
      1. making maximum use of exterior lights;
      2. broadcasting position, flight level and intentions on frequency 121.5 MHz.
    3. notify ATC of the inability to meet RVSM performance requirements, consider declaring an emergency and request clearance to exit MNPS Airspace.
    4. if unable to obtain ATC clearance in a timely manner, to execute appropriate contingency procedures, as specified in ICAO Doc.7030, for leaving the assigned route or track and descending below MNPS Airspace (if operationally feasible); or
    5. if not operationally feasible to execute the appropriate contingency procedures and then continue to alert nearby aircraft and coordinate with ATC.
  • ATC should take the following action:
    1. when notified by the pilot that the aircraft cannot meet RVSM performance requirements, attempt to establish increased vertical, longitudinal or lateral separation;
    2. pass traffic information to the pilot;
    3. if unable to establish increased separation, to consider other options, such as advising the pilot of traffic information and requesting the pilot's intentions;
    4. if the pilot requests clearance to exit RVSM Airspace, then to accommodate the request as expeditiously as possible; and
    5. if notified by the pilot of the loss of all acceptable altimetry systems, to notify the pilot of traffic information, advise aircraft in the vicinity and monitor the situation.

    Primary Altimeters Diverge by More than 60 m (200 ft)

  • The pilot should:
    1. attempt to determine the defective system through established trouble-shooting procedures and/or compare primary altimeter displays with those of the standby altimeter (as corrected from correction cards, if applicable);
    2. if the defective system can be determined, couple the functioning altimetry system to the AKD; or
    3. if the defective system cannot be determined, follow the guidance above regarding failure or unreliable altimeter indications of all primary altimeters, in conjunction as appropriate with ATC.

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;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, Edition 2014/2015

Revision: 20150726
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