B738, Glasgow UK, 2012
B738, Glasgow UK, 2012
On 19 October 2012, a Jet2-operated Boeing 737-800 departing Glasgow made a high speed rejected take off when a strange smell became apparent in the flight deck and the senior cabin crew reported what appeared to be smoke in the cabin. The subsequent emergency evacuation resulted in one serious passenger injury. The Investigation was unable to conclusively identify a cause of the smoke and the also- detected burning smells but excess moisture in the air conditioning system was considered likely to have been a factor and the Operator subsequently made changes to its maintenance procedures.
On 19 October 2012, a Boeing 737-800 being operated by Jet2 on a passenger flight from Glasgow to Alicante carried out a high speed day rejected take off in normal ground visibility and, once stopped, an emergency evacuation of the 193 occupants was completed in which one passenger was seriously injured and 15 others sustained minor injuries.
An Investigation was carried out by the Aircraft Accident Investigation Branch (UK) (AAIB). Data from the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) was successfully downloaded and CCTV, R/T and Surface Movement Radar recordings were also available. In addition, an AAIB passenger questionnaire was sent to each of the 187 passengers and 105 completed ones were returned.
It was noted that the aircraft commander had been designated PF for the flight which was departing at ‘first light’ with the main cabin lighting dimmed. After taxiing out in drizzle through some areas of standing water, a take off was commenced from runway 05 by engaging the TOGA thrust mode of the A/T. During normal acceleration, both pilots became aware of a “strange” smell and at about 80 knots, this became stronger and there was a perception that “slight misting” was occurring on the flight deck. Similar awareness was apparent in the passenger cabin with the unusual smell variously described as “hot oil”, “burning electrics” or “burning rubber”. What appeared to be smoke was coming from the PSUs, visible in the beams of those individual reading lights which were illuminated in the otherwise dimly-lit cabin. This situation prompted the Cabin Service Director (CSD) to use the flight crew interphone to advise of an “urgent” situation in the cabin.
Upon receipt of the CSD call, the aircraft commander called and commenced a rejected take off with the aircraft approaching 100 KIAS. Having brought the aircraft to a stop on the runway, the commander called the CSD to the flight deck and, after receiving a report of conditions in the cabin and observing them directly through the open flight deck door, he ordered an emergency evacuation. Slides and overwing exits - the latter opened without difficulty by passengers - were used and cabin crew observed some passengers recovering personal items from the overhead lockers and thereby delaying the movement towards the exits. The airport Rescue and Fire Fighting Services attended and once all the occupants had left the aircraft, carried out an inspection which found no signs of fire but “detected a faint smell of smoke.”
Despite the fact that there had been a widespread perception of an abnormal situation as the take off began, no defects were subsequently identified which could have led to the “smoke” or fumes that were seen and smelt and analysis of cabin air filters “showed that there were no unusual substances or residues of oil or hydraulic fluid present”. It was considered possible that the slightly later than usual selection of the air conditioning packs on after engine start (although the timing of this selection was still in line with the applicable SOPs) coupled with a short taxi time may have meant that the passenger cabin was slightly warmer than usual for take off. If so, this together with the humid ambient conditions when take off engine thrust increased the available supply of cold air to the cabin to achieve the selected temperature. As the cabin was warm and humid, this sudden influx of cold air “could have caused the formation of mist or fog in the cabin which, in the low lighting conditions, could have given the appearance of smoke or fumes”. However, the Investigation could find no reason for the acrid burning smell which could not subsequently be replicated and there was neither a residual smell in the cabin nor on the clothing of any of the occupants and there were no reports of any negative effects.
The only conclusion possible was that the smell “may have been due to excessive moisture in the (air conditioning) system, vaporising from the ducting as it heated up to its normal operating temperature”.
In respect of reports from some passengers in window seats that they had seen sparks outside the aircraft as the take off was being rejected, no possible source could be identified and it was suspected that what may have been seen in the prevailing wet runway and low light level was the aircraft and runway lights intermittently reflecting off the spray thrown up from the main landing gear as full reverse thrust was deployed.
The returned passenger evacuation questionnaires facilitated a better understanding of the passenger perspective than would otherwise have been possible from observations at the time alone. In addition to passenger perceptions of cabin conditions during the take off roll and subsequent rapid deceleration, useful information in respect of the evacuation itself was gained. It was found that those using the overwing exits had been able to see the markings indicating the rearward direction of movement off the wet wing surface but had found it difficult to see the extent of the drop to the ground in the poor light and some of them had not appreciated that it was necessary to slide down the flap surfaces (which had been set to 40° by the flight crew as required) with some expecting to find a slide available. On the left wing, it was noted that some passengers had successfully slid to the ground and then assisted others to do the same but on the right wing, fewer people did this and some who had exited onto the wing then re entered the cabin and left via the door slides having concluded that there were “no visible signs of danger”. Slide evacuation involved a rapid transit to the bottom due to the wet surface of the slide and some people had difficulty getting out of the way before the next passenger arrived which led to a number of minor injuries as people collided or were knocked over.
The evacuation was timed at 3 minutes and 38 seconds, although this total included the time taken for the aircraft commander to walk through the cabin to check that everyone was off the aircraft. Relevant aspects of the evacuation certification requirements were reviewed. These were noted as including the 90 second evacuation requirement and the certification test assumptions. In respect of the proportion of the 105 passengers who returned their questionnaires, it was noted that the age distribution requirements for the certification test were met. It was noted that the height of the trailing edge of the flap above the ground recorded during certification of the 737 variant involved was 70 inches whereas with the inner flap lowered (as it was for this evacuation) to the prescribed 40°positon, the drop from the trailing edge was only 42 inches.
Safety Action by the Operator subsequent to the event was reported to the Investigation to have been taken as follows:
- Procedures for all post-maintenance engine ground runs have been amended so that both air conditioning packs will be run using engine bleeds and with the cabin temperature selectors in the mid position for five minutes in addition to the existing Aircraft Maintenance Manual requirement for at least five minutes of engine running at idle without load.
- The Passenger Safety Card content has been revised to show that passengers using the overwing exits will need to slide down the trailing edge of the wing and the content of the verbal briefing given by cabin crew to passengers occupying overwing exit seats has been amended to stress the requirement to turn aft immediately after stepping onto the wing through the exit and to then slide down the trailing edge of the wing.
The Final Report of the Investigation was published on 10 October 2013. No Safety Recommendations were made.