On 2 November 2017, an Airbus A320 (EI-GAL) being operated by Aer Lingus on a scheduled international passenger flight from Cork to London Heathrow declared a ‘MAYDAY’ and turned back to Cork after a “strong and persistent” burning smell became apparent in both the flight deck and the passenger cabin as the aircraft climbed through FL260. After stopping on the runway for an assessment of the situation, it was judged safe to taxi to stand and once there, a ‘Rapid Disembarkation’ was ordered which was misinterpreted by some of the 143 passengers as an emergency evacuation and resulted in the over wing exits being used by some.
A Field Investigation was carried out by the AAIU Ireland. Some recorded data relevant to the event was successfully downloaded from the CVR (although only from the area microphone channel) and useful CCTV recordings of the evacuation were also available. However, data from the FDR was missing for the period during which the aircraft was in an emergency electrical configuration in accordance with the required response to the circumstances encountered since no recorder independent power supply (RIPS) was installed.
It was noted that the 44 year-old Captain had a total of 13,571 flying hours of which 9,281 hours were on type. The 37 year-old First Officer, who had been the designated PF for the event flight, had a total of 2,862 flying hours of which 926 hours were on type.
It was established that the sector which resulted in the diversion was the third sector of two successive return flights from Cork to London Heathrow. During the first sector a burning smell had been detected in the flight deck but after the Captain, suspecting that the flight deck floor heaters may be the source had switched them off, the fumes had appeared to dissipate and the flight had proceeded to destination without any recurrence and a corresponding defect entry was made in the Aircraft Technical Log. Maintenance followed the appropriate trouble shooting procedures and checked the APU ducting, the avionics bay and the air conditioning system without finding a fault so the defect was cleared and the fumes did not recur during the second sector.
However, on the third sector similar fumes which this time were described as “strong and persistent” were again detected in the flight deck as the aircraft climbed through FL 260 and it was levelled at FL 270. In response, both pilots donned their oxygen masks, declared a MAYDAY and initiated a return to Cork. The ‘SMOKE/FUMES/AVNCS SMOKE’ Checklist was followed. After the initial part of this Checklist had not enabled the identification of the source of the fumes, the second part of it was run. This involved putting the aircraft into an emergency electrical configuration in which the normal electrical generation system was replaced by the RAT and required the aircraft to be flown manually and at this point, the Captain took over as PF. This electrical system reselection was not followed by any dissipation of the fumes and in accordance with the Checklist, the aircraft generators were switched on again shortly before landing “to recover normal braking”. A normal landing on runway 35 at Cork followed after approximately 50 minutes airborne and, after satisfying himself that it was safe to continue, the Captain elected to taxi to the allocated parking stand and was accompanied by the attending RFFS vehicles.
Once on stand, the aircraft engines were shut down and the crew made a further assessment of the situation noting that fumes were still present in the flight deck. After a brief exchange with both the Senior Cabin Crew Member (SCCM) and the attending ground staff, the Captain made a PA announcement saying “Attention, Attention, this is the Captain, disembark the aircraft immediately” as per the option specified in Aer Lingus SOPs separately from an Emergency Evacuation. Following this announcement, most passengers exited the aircraft using the left side doors at the front and rear of the cabin but passengers in the emergency exit seat rows opened the over wing emergency exits and “approximately 32 passengers disembarked onto the aircraft wings” of which half then used the corresponding escape slides. The others returned to the passenger cabin and subsequently left the aircraft using the front and rear doors. CCTV evidence showed that almost six minutes elapsed from the time the first passenger left the aircraft until the last one did so with assistance. CCTV recordings also confirmed that once on stand, the passengers would have been able to see the fire service vehicles and the personnel who had taken up positions around the aircraft and manned fire hoses. No injuries occurred during the evacuation / disembarkation of the aircraft.
Intended ‘Rapid Disembarkation’
The confusion amongst the passengers led to a combination of the intended rapid disembarkation and an emergency evacuation. It was noted that Airbus Flight Crew Operating Manual (FCOM) does not include reference to ‘Rapid Disembarkation’ and the procedure which the Captain followed had been formulated by the airline. It envisaged passengers leaving their cabin baggage behind but exiting through the normal left side exit door(s) whereas the FCOM Emergency Evacuation involves all available exits and their escape slides being used.
The absence of any regulatory requirement for the airline to have a ‘Rapid Disembarkation’ procedure was also noted with the airline’s procedure being developed with the presumed awareness (the aircraft operator is an active IATA member) of the Third Edition (2017) of the IATA Cabin Operations Safety Best Practices Guide. This was noted to include (in section 16) a suggested procedure which stressed that the announcement used to initiate a rapid disembarkation “should be different from the (emergency) evacuation command”.
It was found that the Aer Lingus rapid disembarkation procedure had originally been only for cabin crew use but had “recently been expanded to be used by flight crew following an occurrence in the USA where ground equipment caught fire close to an aircraft when passengers were disembarking” and had been “promulgated to flight and cabin crew using internal memos known as Crew Instructions and in recurrent training”. The expanded procedure stated that a Captain wanting to order a rapid disembarkation could do so (as the Captain in this case had done) by using the announcement “attention attention this is the Captain, disembark the aircraft immediately” with the only difference between this and the wording of an order to evacuate being the substitution of “disembark” for “evacuate”.
It was noted that relevant EASA Guidance Material did not explicitly require an operator to include emergency evacuation commands (or those related to any other “expedited disembarkation procedure” in their passenger pre-flight safety briefing and was merely intended to ensure that crew members explain to passengers that they must comply with crew members’ instructions. However, it did explicitly state that briefings to passengers seated at over wing exits should include “recognition of emergency commands given by the crew”. The Investigation noted that the EASA assessment of safety risks associated with emergency evacuations (or rapid disembarkations) did not appear to take account of passenger experiences during actual evacuations and also the EASA “opinion that emergency evacuation is an extremely complex topic and that being overly prescriptive in guidance material will not always be helpful to the operator, or result in the best safety outcome”.
The Investigation contrasted the potential scope for confusion in the action which may be required of passengers in abnormal aircraft evacuations with the corresponding communications required by the SOLAS (Safety of Life At Sea) Regulations for passenger ships where all passengers must be briefed on a specific signal and told what they must do if they hear it.
Two previous investigations where confusion between rapid disembarkations and emergency evacuations had been identified were noted by the Investigation as having been a July 2013 Boeing 777-300 event at Paris CDG and an August 2013 Boeing 757-200 event at London Gatwick. The latter investigation was noted as having highlighted “the importance of flight crew communicating their intentions to cabin crew prior to initiating a rapid disembarkation” and having stressed in this context that “the language used in passenger commands should be unambiguous”.
The Airworthiness Context
The judgement of the Captain that a turn back and, on arrival, a rapid disembarkation was necessary after the detection of fumes was informed by their lack of knowledge of the origin of the fumes and the potential for these fumes to be a precursor to a more hazardous situation. The origin of the fumes in the flight deck was found after flight to have been wear on the rear bearing in the avionics bay fan. It was noted by the Investigation that both the aircraft manufacturer and the fan OEM were already aware of similar previous fumes events attributable to the same avionics fan bearing problem. As an initial response to the problem had been the issue of a SIL recommending removal and overhaul of these fans every 10,000 flight hours which the operator of the aircraft involved in this event had opted to implement. However, the start of this new policy had occurred with many of the fans already well in excess of the new 10,000 hours in service and the fan which had generated fumes due to wear in this case had not yet been replaced but had accumulated 15,745 flight hours.
The formally documented Findings of the Investigation included the following:
- The briefing given to passengers seated in the over wing emergency exits did not include the commands that would be used by flight or cabin crew in the event of an emergency, nor was it required to.
- The fumes did not readily dissipate and the Flight Crew commenced the second stage of the ‘SMOKE/FUMES/AVNCS SMOKE’ Checklist, which required them to put the aircraft temporarily into an emergency electrical configuration.
- The emergency electrical configuration resulted in the FDR being de-energised so that it did not record any data during that period.
- The wording (to be) used by the Commander in the event of a rapid disembarkation is very similar to the wording for an emergency evacuation.
- The Cabin Crew then made an announcement on the aircraft PA system asking passengers to “use the nearest available exit”.
- The relevant EASA Guidance Material does not explicitly recommend that passengers should be briefed in advance on the emergency commands that might be used by flight or cabin crew. However it does suggest that passengers seated in emergency exit rows should be briefed on emergency commands.
The Probable Cause of the Serious Incident was determined as “unintended use of the emergency over wing exits, following a return to the departure airport, due to fumes entering the cockpit”.
Five Contributory Factors were also identified
- Rear bearing failure of the avionics bay blower fan.
- Heightened alertness among passengers due to diversion.
- Visual cues to passengers who saw emergency responders outside the aircraft.
- Similarity between rapid disembarkation instruction and emergency evacuation instruction.
- Direction to the passengers following the rapid disembarkation direction to “use the nearest available exit”.
Safety Action taken as a result of the event included the following:
- the Aircraft Operator undertook a review of their Rapid Disembarkation Procedure and “intends to revise the guidance material which addresses an escalation from a rapid disembarkation to a full evacuation”.
- the Avionics Fan OEM made a ball-bearing health monitoring system available for retrofit as an interim measure in May 2018 and is “anticipating that a redesigned fan will replace the current design during 2019”.
The Final Report of the Investigation was published on 7 May 2019. No Safety Recommendations were made.