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Emergency Descent: Guidance for Controllers
From SKYbrary Wiki
There is no set of ready, out-of-the-box rules to be followed universally. As with any unusual or emergency situation, controllers should exercise their best judgment and expertise when dealing with emergency descent situations. A generic checklist for handling unusual situations is readily available from EUROCONTROL but it is not intended to be exhaustive and is best used in conjunction with local ATC procedures.
This article provides guidance for controllers on what to expect and how to act when dealing with an emergency descent which takes place in controlled airspace. There are some considerations which will not only enable the controller to provide as much support as possible to the aircraft involved, but to also maintain the safety of other aircraft in the vicinity and of the ATC service provision in general.
Useful to Know
There are various reasons why the flight crew might initiate an emergency descent. These include but are not limited to loss of pressurisation and in-flight fire. Many flight crew drills encourage emergency descents to continue to the higher of 10,000 feet or MSA from where the aircraft may then seek the shortest route to a suitable diversion aerodrome.
An emergency descent could be initiated without prior warning. Depending on the circumstances, the flight crew could begin a high vertical speed descent without warning if the safety of the aircraft is at risk, which is in line with the guiding principle applied to the prioritisation of flight deck tasks: Aviate, Navigate, Communicate.
When an aircraft operated as a controlled flight experiences a malfunction requiring an emergency descent, ICAO EUR Region procedures state that crew shall, if able:
- Initiate a turn away from the assigned route or track before commencing the emergency descent (ICAO Doc 7030, para 22.214.171.124). There is no prescription in respect of the direction in which such a turn should be made and not all States follow this part of the ICAO model anyway. Some military training advises that when beginning a un-communicated descent, it should be made to the left to allow the aircraft commander the best line of sight but this is less common in civil air transport operations.
- Advise the appropriate air traffic control unit as soon as possible of the emergency descent
- Set transponder to Code 7700 and select the Emergency Mode on the ADS/CPDLC system, if applicable
- Turn on aircraft exterior lights
- Watch for conflicting traffic both visually and by reference to ACAS
- Coordinate its further intentions with the appropriate ATC unit
Anticipated Impact on Crew
A wide range of practical problems could arise in the cockpit following the decision to initiate an emergency descent:
- Increased workload in the cockpit - During the initiation of an emergency descent, the workload becomes intense as the crew try to resolve the problem with the aircraft, fly the aircraft safely, and plan for the descent.
- Emergency descent procedure - Descent is initiated in accordance with the operator's emergency procedures and associated training.
- Situational awareness issues - The crew may struggle to maintain full situational awareness.
- Communication problems - Several problems connected with air-ground communications could arise including late communication, poor message quality due to donning of oxygen masks, and non-standard phraseology.
What to Expect
- Descent without warning - Pilots are trained to announce any emergency descent promptly and to subsequently advise ATC of their intentions as soon as practicable. However, during the early stages of an emergency descent, the workload is high and controllers should expect to hear little more than the announcement of the descent in the first few minutes.
- Delay in emergency squawk - the setting the 7700 emergency squawk may be delayed because, although this action is included in most pilot memory drills for emergency descent, it is often the final item.
- Poor quality RTF - poor communication quality, due to changes in the sound of speech including a distorted sound spectrum, because of the effect which the donning of oxygen masks may have on the clarity of transmissions.
- Interruption to RTF - if oxygen masks are donned, the procedure to do so will cause a temporary interruption to both transmit and receive functions. Such temporary interruptions may also occur due to the need for the non handling pilot to communicate with the cabin crew on the crew interphone using a channel selector which temporarily replaces the ATC frequency at a time when the other pilot may be too busy to substitute attention to ATC if the intention to descend has already been broadcast.
What to Provide
Best practice embedded in the ASSIST principle could be followed (A - Acknowledge; S - Separate, S - Silence; I - Inform, S - Support, T - Time) :
A - acknowledge the descent (the declared malfunction and emergency if applicable), ask for the crew’s intentions when the situation permits
S- separate other aircraft from the emergency aircraft and issue essential traffic information about the emergency descent
S - silence the non-urgent calls (as required) and use a separate frequency where possible to talk to the emergency aircraft;
I - inform the adjacent ATC units if the aircraft is approaching or is near to their areas of responsibility; inform your supervisor and relay the flight crew’s intentions
S - support the flight with any information requested and deemed necessary. If necessary inform the crew of the minimum safe altitude.
T - provide time for the crew to assess the situation, don’t press with non urgent matters.
The controller should be prepared to:
- Acknowledge the emergency on RTF
- Take all necessary action to safeguard all aircraft concerned
- Provide a heading, if requested or otherwise necessary for risk management
- Provide separation or issue essential traffic information, as appropriate
- State the applicable minimum safe altitude, if necessary (REMEMBER: The aircraft should not descend below the lowest published minimum altitude which will provide a minimum vertical clearance of 300m (1000 ft) or in designated mountainous terrain 600m (2000 ft) above all obstacles located in the area specified.)
- Make an emergency broadcast if necessary
- After emergency descent, and when the situation permits, ask for pilot intentions and other important information, such as :
- Intention to divert
- Injuries sustained by occupants
- Damage to aircraft
- Consider the aircraft as remaining in an emergency situation until confirmed otherwise. The aircraft could be ready to continue flight without any further complications after the emergency descent if no structural damage was sustained and there are no significant system malfunctions. However, be aware than often a crew is unable to assess the type or extent of any damage whilst in flight.
- Personal Awareness - ATCOs should always be monitoring the course and altitude of traffic in his/her sector. Being constantly aware of any ongoing deviations should provide precious time for vectoring of nearby traffic.
- Adequate Reaction - Some of the possible actions: transfer all other aircraft to another frequency (possible message to all stations to increase awareness); leave the emergency traffic on the current frequency; increase the volume of the receiver; have a colleague (a separate pair of ears) to also listen to all transmissions from the aircraft.
- Technological Limitations - Try to keep aircraft within radar cover. Have in mind the features of the existing radar system.
- Organisational Awareness - Adequate provision of ATC service during emergency situations should be an objective at administrative level. Periodic training and drills are likely to improve intra-organisational coordination.
Accidents and Incidents
The following events on the SKYbrary database involved an emergency descent:
- A319, en-route, Free State Province South Africa, 2008 (On 7 September 2008 a South African Airways Airbus A319 en route from Cape Town to Johannesburg at FL370 received an ECAM warning of the failure of the No 1 engine bleed system. The crew then closed the No. 1 engine bleed with the applicable press button on the overhead panel. The cabin altitude started to increase dramatically and the cockpit crew advised ATC of the pressurisation problem and requested an emergency descent to a lower level. During the emergency descent to 11000 ft amsl, the cabin altitude warning sounded at 33000ft and the flight crew activated the cabin oxygen masks. The APU was started and pressurisation was re-established at 15000ft amsl. The crew completed the flight to the planned destination without any further event. The crew and passengers sustained no injuries and no damage was caused to the aircraft.)
- A320, en route, north of Marseilles France, 2013 (On 12 September 2013, pressurisation control failed in an A320 after a bleed air fault occurred following dispatch with one of the two pneumatic systems deactivated under MEL provisions. The Investigation found that the cause of the in-flight failure was addressed by an optional SB not yet incorporated. Also, relevant crew response SOPs lacking clarity and a delay in provision of a revised MEL procedure meant that use of the single system had not been optimal and after a necessary progressive descent to FL100 was delayed by inadequate ATC response, and ATC failure to respond to a PAN call required it to be upgraded to MAYDAY.)
- A320, en-route, north of Öland Sweden, 2011 (On 5 March 2011, a Finnair Airbus A320 was westbound in the cruise in southern Swedish airspace after despatch with Engine 1 bleed air system inoperative when the Engine 2 bleed air system failed and an emergency descent was necessary. The Investigation found that the Engine 2 system had shut down due to overheating and that access to proactive and reactive procedures related to operations with only a single bleed air system available were deficient. The crew failure to make use of APU air to help sustain cabin pressurisation during flight completion was noted.)
- A320, en-route, northeast of Granada Spain, 2017 (On 21 February 2017, an Airbus A320 despatched with the APU inoperative experienced successive failures of both air conditioning and pressurisation systems, the second of which occurred at FL300 and prompted the declaration of a MAYDAY and an emergency descent followed by an uneventful diversion to Alicante. The Investigation found that the cause of the dual failure was likely to have been the undetectable and undetected degradation of the aircraft bleed air regulation system and whilst noting a possibly contributory maintenance error recommended that a new scheduled maintenance task to check components in the aircraft type bleed system be established.)
- A320, en-route, west southwest of Karachi Pakistan, 2018 (On 5 March 2018, the crew of an Airbus A320 in descent towards Karachi observed a slow but continuous drop in cabin pressure which eventually triggered an excessive cabin altitude warning which led them to don oxygen masks, commence an emergency descent and declare a PAN to ATC until the situation had been normalised. The Investigation found that the cause was the processing of internally corrupted data in the active cabin pressure controller which had used a landing field elevation of over 10,000 feet. It noted that Airbus is developing a modified controller that will prevent erroneous data calculations occurring.)
- A333, en-route, south of Moscow Russia, 2010 (On 22 December 2010, a Finnair Airbus A330-300 inbound to Helsinki and cruising in very cold air at an altitude of 11,600 metres lost cabin pressurisation in cruise flight and completed an emergency descent before continuing the originally intended flight at a lower level. The subsequent Investigation was carried out together with that into a similar occurrence to another Finnair A330 which had occurred 11 days earlier. It was found that in both incidents, both engine bleed air systems had failed to function normally because of a design fault which had allowed water within their pressure transducers to freeze.)
- A388, en-route, northern Afghanistan, 2014 (On 5 January 2014, an Airbus A380-800 en route to Singapore at night made an emergency descent and diversion to Baku after a loss of cabin pressure without further event. The Investigation attributed the pressure loss to a fatigue crack in a door skin which was initiated due to a design issue with door Cover Plates, which had not been detected when the Cover Plate was replaced with an improved one eighteen months earlier. Safety Issues related to cabin crew use of emergency oxygen and diversions to aerodromes with a fire category less than that normally required were also identified.)
- AS55, vicinity Fairview Alberta Canada, 1999 (On 28th April 1999, an AS-355 helicopter suffered an in-flight fire attributed to an electrical fault which had originated from a prior maintenance error undetected during incomplete pre-flight inspections. The aircraft carried out an immediate landing allowing evacuation before the aircraft was destroyed by an intense fire.)
- Explosive Depressurisation
- Rapid Depressurisation
- Gradual Depressurisation
- Pressurisation Problems: Guidance for Controllers
- In-Flight Fire: Guidance for Controllers
- Pressurisation Problems: Guidance for Flight Crews
- Unexpected Events Training (OGHFA BN)
- Safety Warning Reminder Message, 20100722, Emergency Descent in High Traffic Density Situations
NATS Flight Deck Procedures Video
There will be times when controllers will have to cope with unusual situations such as weather avoidance or aircraft emergencies. It is important for controllers to have knowledge of the flight deck procedures that will be used by aircrew in such situations. The following video describes the generic procedures followed by aircrew in certain unusual situations:
|Abnormal and Emergency Operations|
- Guidelines for Controller Training in the Handling of Unusual/Emergency Situations
- ATC Refresher Training Manual, ed.1.0, March 2015