An emergency descent is a manoeuvre for descending as rapidly as possible to a lower altitude (potentially, to the ground for an emergency landing). The need for this manoeuvre may result from an uncontrollable fire, a sudden loss of cabin pressurization, or any other situation demanding an immediate and rapid descent. The objective is to descend the aircraft as soon and as rapidly as possible, within the structural limitations of the aircraft.
Crews should follow company approved emergency procedures and manufacturer's guidance in the event that an emergency descent is necessary.
This article considers some aspects of airmanship which are applicable to all aircraft and situations.
At the first indication of smoke or fumes, a pressurisation problem or symptoms of Hypoxia, the flight crew should immediately don oxygen masks. Without supplemental oxygen, the crew can be quickly incapacitated by smoke and, at typical turbine powered aircraft cruising altitudes, the Time of Useful Consciousness can be less than one minute in the event of a explosive or rapid depressurisation.
Many operators direct that the captain will conduct any required emergency descent and will so define this responsibility in the Company Operations Manual. However, the first officer must also be able to effectively complete an emergency descent in the event that the captain is incapacitated or absent from the flight deck.
Initiation of an emergency descent is done as a memory item drill in most aircraft types. Once the descent has been initiated, it is standard procedure to confirm that all required actions have been completed by referring to the appropriate checklist in the Quick Reference Handbook (QRH). The autopilot of many current generation aircraft can be used by the PF to carry out an emergency descent profile and many manufacturers recommend that the autopilot be left engaged for the manoeuvre. Some aircraft types, such as many of the newer Gulfstream business jets, have an auto-descent capability which arms when the aircraft is above FL400 with the autopilot engaged and will automatically manoeuvre and descend the aircraft following a depressurisation if, following a brief interval, there has been no action taken by the pilots (incapacitation). An emergency descent can also be flown manually.
ICAO Doc 7030 directs the following actions in the event that an aircraft experiences a sudden decompression or a (similar) malfunction requiring an emergency descent:
- Initiate a turn away from the assigned route or track before initiating the descent (note that in very congested airspace, this may not be advisable and that in some regions, such as the North Atlantic, there are specific contingency procedures to be followed. Certain regions of Europe have, in their AIPs, denoted that an emergency descent should be conducted on their cleared track unless an immediate conflict exists)
- Advise the appropriate air traffic control unit as soon as possible of the emergency descent
- Set the transponder code to 7700 and select Emergency Mode on the Automatic Dependent Surveillance (ADS) / Controller Pilot Data Link Communications (CPDLC) equipment as appropriate. This would trigger an alert on the controller's situation display which would facilitate better response on their part (e.g. they will start to clear the airspace around the aircraft, inform the supervisor, plan further action, etc.). Such an alert is especially helpful in case of vertically split sectors as it will override any applied level filters and will draw the attention of the lower sector to the imminent entry of an aircraft in distress.
- Turn on all exterior lights
- Watch for traffic both visually and with reference to ACAS/TCAS (if equipped)
- Coordinate further intentions with the appropriate ATC unit
Ensure that altimeters are set to local QNH or QFE as appropriate. An initial target altitude which is the higher of MORA, MOCA, MEA (as appropriate to routing and aircraft capability), or a specified Company/manufacturer value (often 10,000') will be selected. In mountainous terrain, specific escape routes may be required. Temperature corrections should be applied as appropriate.
Unless structural damage is suspected, the aircraft should be descended at or near maximum speed (Vmo) with thrust at idle and flight spoilers or speed brakes extended. If structural damage is suspected, the aircraft should be flown at, or close to, the indicated airspeed (IAS) at which the failure occurred.