A British Airways Airbus A320-200, registration G-EUYB performing flight BA-709 from Zurich (Switzerland) to London Heathrow,EN (UK) with 139 passengers and 6 crew, was just established on the localizer Heathrow’s runway 27L when the crew declared PAN PAN reporting smoke in the cabin. While ATC sent a number of aircraft already released from the holding patterns for approach back into the holding patterns, the aircraft continued for a safe landing on runway 27L about 4 minutes later, emergency services were in their stand by positions. The aircraft vacated the runway and stopped on the parallel taxiway for about an hour, emergency services boarded the aircraft through the forward right hand door via a mobile stair and examined the aircraft. The passengers disembarked via the stairs. A number of passengers and cabin crew required medical attention for smoke inhalation. Both pilots received minor injuries.
A BA Lounge was cleared to accomodate the passengers of the aircraft and their families.
The occurrence aircraft remained on the ground in London for about 5 days.
On Oct 3rd 2019 the AAIB reported there were smoke and fumes on the flight deck, the first officer was taken to hospital after landing. The highest degree of injuries is unknown so far, the AAIB thus rated the occurrence a serious incident so far and opened an investigation.
On Jul 30th 2020 the AAIB released their final report releasing the conclusions regarding this and five similiar events:
While it has not been possible to positively identify the compound that was responsible for the fumes and odours experienced in G-EUYB, or any of the other recent events, a number of common factors have been identified. The majority of events occurred after the aircraft had been parked or operated in precipitation. The fumes become apparent during the later stages of the descent, sometimes preceded by a minor event during the climb phase. The generation of fumes appears to be transient; they dissipate rapidly and leave no detectable trace. No link between changes to engine power or changes in other system settings and the generation of fumes was identified.
In some cases, the presence of fumes has resulted in physiological reactions which have interfered with a flight crew member’s ability to carry out their normal duties. However, by following the smoke and fume checklist, and donning oxygen masks the flight crew were able to ensure the continued safety of the aircraft.
The AAIB annotated: “Numerous other similar fume events have been reported to the AAIB and the CAA. This report reviews five other similar events which occurred with the same operator on the same aircraft type. It was not possible to identify the cause of these events, but, several common features have been identified.”
The AAIB reported the sequence of events:
The incident crew reported for the return sector to Heathrow at 0345 hrs for a scheduled departure at 0510 hrs. Both flight crew reported that they were well rested. The initial departure from Zurich was uneventful. It was still raining during the departure and the aircraft entered cloud at approximately 1,000 ft agl and remained in cloud for the majority of the climb. Shortly after passing through FL100 the flight crew detected a slight odour on the flight deck. The commander initially thought the smell was coming from the galley ovens. The co-pilot described it as a “sweaty socks” smell; he reported that he had smelt similar smells on this type of aircraft before, but this was stronger than he had previously experienced. The commander was concerned that they were preconditioned to detect fumes because of their previous experience of fume events and their discussion the evening before. He proposed they waited 30 seconds prior to taking any action to see if the smell dissipated. After 30 seconds the smell had gone. The crew discussed further options and agreed to continue the flight.
The flight crew’s previous experience suggested that if the smell was going to reoccur it was most likely to occur when thrust was reduced for descent so, during the cruise, they discussed their actions if the smell returned and reviewed the SMOKE / FUMES / AVNCS SMOKE checklist. They briefed for the co-pilot to fly the descent and approach for the commander’s landing.
The initial descent into Heathrow was uneventful. There were clear skies throughout the descent. The aircraft held briefly at BIGGIN HILL and was then radar vectored for an ILS approach to Runway 27L. As the aircraft intercepted the localiser ATC requested the aircraft to reduce speed to 160 kt. The aircraft was slightly above the glideslope so the co-pilot used speed brake to intercept the glideslope from above and decelerate.
Having intercepted the ILS, as the aircraft passed through 4,000 ft both flight crew detected a sudden, very strong smell. The commander described it as a “manure smell”; “like a field which had just been muck spread”. He described the smell instantly “hitting him” in the back of the throat. There was no smoke and no obvious source of the smell. The co-pilot described it as a “strong sweaty socks” smell. He reported feeling itchy skin around his eyes and a scratchy throat. The commander took control and instructed the co-pilot to put on his oxygen mask. Once the co-pilot was on oxygen and communication was re-established the co-pilot took control whilst the commander donned his oxygen mask.
The commander requested an early hand-over from the approach controller to the tower controller, which was granted. He then made a PAN call to Heathrow Tower; he reported that they had fumes on the flight deck and required a priority landing. The flight crew then selected the landing gear down and landing flap then decelerated to the final approach speed. ATC advised the two aircraft ahead of G-EUYB and one behind to expect a go-around and then instructed them to go-around in sequence. The flight crew discussed options and agreed the safest course of action was to continue the approach. The aircraft was stable at 1,000 ft agl. The commander elected to use Autoland. He advised ATC that they would vacate onto the parallel taxiway where they would require an inspection from the emergency services. The aircraft landed at 0644 hrs, vacated the runway at N6 and stopped on Taxiway A.
Once the aircraft had stopped the commander asked the co-pilot to complete the after landing procedure and the initial actions of the SMOKE / FUMES / AVNCS SMOKE checklist.
The co-pilot made initial contact with ‘Fire 1’ and advised them that they had fumes on the flight deck and were completing some checklists. The commander made the Alert Call and gave the Senior Cabin Crew Member (SCCM) a NITS briefing via the interphone. The SCCM confirmed there was no smell in the cabin and the passengers were not aware of anything unusual. The commander then spoke to Fire 1 and made an announcement to the passengers to explain what was happening.
The co-pilot removed his oxygen mask briefly to confirm if the fumes were still present. He confirmed the fumes were still present so the flight crew decided to shut down both engines and open the flight deck windows. At this stage the co-pilot started to feel nauseous. The Auxiliary Power Unit (APU) was started for electrical power and the engines were shutdown.
The co-pilot then vomited out of the flight deck window. The commander initially planned for the aircraft to be towed to a parking stand but as it became apparent that the co-pilot needed urgent medical attention, he requested steps be brought to the aircraft. The co-pilot went to the aircraft toilet and continued to vomit. The SCCM came on to the flight deck to assist the commander. The SCCM reported that he smelt a “chemical smell”, “a clean clinical smell” on the flight deck. He confirmed that there was no smell in the cabin.
The fire service brought access steps to the aircraft. Communication between the fire service and the flight crew was challenging due to the wind noise with the flight deck windows open.
The fire service initially thought the co-pilot was trying to exit the aircraft via the flight deck window so positioned the step adjacent to the window. However, after further discussion the steps were repositioned to Door 1 right. It took the fire service some time to position the steps at the door due to the turning circle of the vehicle, limited space on the taxiway and a concern that the vehicle would become stuck in soft grass at the side of the taxiway. The aircraft door was opened at approximately 0706 hrs and fire crews and paramedics entered the aircraft. The fire crew inspected the aircraft and reported that they could not detect any unusual smells or fumes. A member of the operator’s engineering staff also boarded the aircraft after the event and did not detect any fumes or odours.
The co-pilot and commander were assessed by the paramedics and both taken to hospital. The passengers subsequently disembarked via steps onto coaches and were transported to the terminal. None of the passengers or cabin crew reported any ill effects.
The co-pilot and commander were released from hospital later the same day.
The AAIB reported the commander had been involved in another fume event on Dec 21st 2018 on the flight from Heathrow to Geneva and required hospital treatment following the flight (The Aviation Herald was not able to report that one due to lack of sufficient evidence). The first officer had been involved in another smoke event in Valencia on Aug 5th 2019, see Accident: British Airways A321 at Valencia on Aug 5th 2019, smoke on board.
The aircraft underwent several “work packages” following the landing in Heathrow for examination and determination of the causes of the smoke. The AAIB summarized the results:
G-EUYB was withdrawn from service and all the work packages were completed. No fumes or abnormal odours manifested themselves during these tests and the aircraft was released to service. However, four further events were reported up to the end of December 2019. In each case no faults could be found during the troubleshooting.
The AAIB analysed:
This event was one of many very similar occurrences that had taken place with this operator and other operator’s fleets of aircraft. These events had been reported via the operator’s safety system and as MORs to the CAA. With the majority of these events, no immediate adverse effects on the flight crew were reported. It is not known if there are or will be any long-term health effects.
The fumes and odours are usually not visible but have a similar characteristic pungent smell. In some cases, this has resulted in stinging eyes and the sensation of “catching in the throat”. However, it does not have the same effect on every individual. In this case, G-EUYB, one of the flight crew was affected to the extent they were incapacitated by feelings of nausea. After removing their oxygen mask, they vomited and were eventually taken to hospital for checks. Regarding the wider issue, crew opinions vary; some individuals describe it as an irritation and as “an annoying” trait of the aircraft type, whereas others consider it a significant flight safety hazard and a cause for concern.
Abnormal events in the cockpit, such as the presence of smoke and fumes, could be the first indication to the flight crew of a hazard which threatens the safety of the aircraft and requires an immediate response from the flight crew. The unique way individuals interpret smells, coupled with their unconscious response to a stressful situation can result in markedly different physiological reactions between flight crew members. The donning of oxygen masks as part of the flight crew actions when smoke or fumes are detected should isolate them from the source of the smoke and fumes.
In all the cases mentioned in this report, the possibility of influences from outside the aircraft has been considered, such as the use of aircraft washing fluids and detergents or anti-icing fluids. However, in most cases, washing or anti-icing operations had not been carried out prior to the flight in which the event occurred.
Damp and rainy conditions were often reported during these events and so is considered a potential factor. It is not known specifically why this is the case but ambient humidity around or within the aircraft and its systems may be a contributory factor.
Actions by the manufacturer
The manufacturer has been investigating fume events based on reports and information received from operators. The nature of the unidentified fume events has meant there has been no residual physical evidence of the fumes which could be identified as the source and thereby lead to specific measures to address the causes of these events. The unpredictable nature of the events has also meant that it has not been possible to construct an experimental flight test schedule to capture more data. This has left the manufacturer reliant on reported data, making the issue difficult to resolve in practical terms.
Technical cause It has not been possible to obtain a sample of these fumes for scientific analysis. However, there are a few features and characteristics which may be relevant. The evidence indicates that it is likely that these fumes are derivatives of contaminants entering the ECS. It may not be a single compound but a combination of compounds which react and then become airborne in the bleed air supplies passing through the ECS. The fumes may have similar traits to hydrocarbon compounds combined with water vapour in low concentration which are liberated as water vapour condenses when it enters cooler conditions, for example as it passes into the flight deck or cabin via ducts. The suggestion that aircraft operating in damp or rainy conditions are more susceptible to fume events may add some weight to this theory. This is supported by the manufacturer’s observation that the fumes decrease, or in many cases disappear, when the humidity of the air in the cabin decreases at higher cabin altitudes.
Consideration has also been given to whether the source may have been from plastic materials used within the ECS ducting, but this is thought less likely because the plastics tend to be used in the delivery of ECS air to the cabin rather than in production where hot and high energy air is used. The aircraft sub-variants, engine types and ages of the aircraft in which fume events occurred was also considered. This produced no conclusive evidence linking these events to a specific aircraft subset.
The operator of G-EUYB had developed a post fume/odour and smoke event maintenance procedure to tackle the issue. Its development was based on experience and findings over several years and has been successful in identifying the source of many of the previous events. The procedure is based around looking for evidence within supplier and receiver systems.
It directs maintenance staff to look for evidence to establish whether engine air/ oil seals have malfunctioned. However, in the most recent set of cases, the operator’s post-fume check procedure has not been able to pinpoint faults or malfunctions which could have generated fumes. In all but one of these recent cases the engines have not been the source of the fume events The procedure for start-up and shutdown of the APU seems to have an effect. The operator has recently advised all flight crew to ensure the correct delay is applied between starting the APU and selecting bleed air and this seems to have reduced the number of events.
The theory is that at APU start the generator and load compressor run-up from cold. It then takes a short amount of time for the bearings and seals to ‘warm’ up and stabilise to be effective. If bleed air from the load compressor is selected early, oil mist or residues can be released and drawn into the ECS airflow.
It does not seem logical that the APU can be a source of these events particularly as they often occur on descent whilst the APU is not in use. However, it is possible that entrained contaminants generated on initial APU start may linger, either as vapours or condensate, upstream of the ECS packs whilst the more predominant bleed air from the engines supplies the system. These contaminants are then entrained into the ECS system as air flow and temperature changes take place during descent. ECS system schematic diagrams are not able to show where and how this may take place. However, in practice the ECS consists of numerous straight, bent and curved ducts, leading to and from valves and conditioning components positioned and shaped alongside numerous other unrelated components. It is therefore possible that small amounts of contaminants could adhere to various internal surfaces or become trapped in ‘pockets’ within the system.