British Airways A319 near Zurich on Jul 24rd 2015, smoke and fumes in the cabin and cockpit
Last Update: November 1, 2018 / 18:50:06 GMT/Zulu time
On Jul 27th 2015 the Swiss SUST reported that the aircraft was holding northwest of Zurich when fumes became perceptible in the aircraft. The crew donned their oxygen masks, declared an urgency and executed an immediate approach to Zurich. The occurrence was rated a serious incident, the SUST is investigating the occurrence.
In Oct 2018 the SUST released their final report concluding the probable cause of the serious incident was:
The serious incident can most probably be attributed to the air conditioning packs being contaminated with engine oil from the APU, which was dripping from the APU generator drain plug onto the APU air inlet duct in small quantities. From the air inlet duct, the oil was drained to the outside via a drain mast, which is located directly behind the APU air inlet. It is therefore probable that the leaked oil reached the APU air inlet when the APU was in operation on the ground, potentially assisted by the effect of tailwind.
The flight crew had the aircraft inspected after the first occurrence of fumes and then continued with their duties. The cabin crew felt unable to continue with their duties after this event. Both decisions are understandable because the adverse effect caused by malodorous or even toxic fumes can vary depending on the person’s location within the aircraft.
Cleaning of both the air supply and inlet duct appeared to rectify the problem. However, as the oil leak in the APU had obviously not been discovered, this resulted in another contamination of the air supply, which this time only had an effect some time after the APU had been switched off.
The crew acted in a safety-conscious manner by protecting themselves and immediately performing a precautionary landing.
The SUST reported the events during flight preparations (quoted in full):
On 24th July 2015, the crew of the Airbus A319, registered as G-EUPJ, began boarding passengers on time for the scheduled flight from London Heathrow to Zurich with flight number BA 718. The auxiliary power unit (APU) and air conditioning pack 1 were switched on. The flight crew then noticed an unusual odour. Both pilots agreed that this odour occurs when oil is heated and evaporates. This fume smell is often described as smelling like ‘old socks’ or smelling musty and foul.
After the pilots had noticed the smell, they asked the deputy cabin crew manager, who is known as the purser at British Airways and was in the rear galley, whether she smelt something too. She said that she could, and described the odour as what she knew to be a fume smell. She added that she had previously experienced a fume event and that it smelt exactly the same. According to the captain’s statement, he switched on the second air conditioning pack before or after the conversation with the purser so that the air conditioning would operate normally. After the purser had explained that she had noticed the same odour at the rear of the aircraft, the flight crew turned off the air conditioning by switching off both air conditioning packs and the APU bleed air. The smell subsequently dispersed. They reported the problem to the technicians and then had the passengers disembark for the period of the fault investigation.
The technicians suspected that the heavy rainfall at London Heathrow had washed oil residues on the aircraft fuselage into the APU air inlet and that due to the burning of these oil residues in the APU, this fume smell had been spread around the aircraft via the air conditioning, which was running on APU bleed air on the ground. After consultation with their managers, the technicians decided to disable the APU bleed air and to flush out the air conditioning packs using bleed air from one engine in order to remove remaining oil residues and fumes.
For the time it took the technicians to complete their job, the flight crew made their way to the terminal to wait there. Two cabin crew members reported physical complaints. The entire cabin crew subsequently decided to withdraw from this flight. When the captain briefly returned to the aircraft in the meantime to check the progress of the work, he could already notice the smell halfway along the passenger boarding bridge to the aircraft. At that time, the technicians were operating the air conditioning packs using the APU, and the engine had not yet been started. After a brief conversation, the captain returned to the terminal to continue waiting.
Once the air conditioning packs had been flushed out using bleed air from one engine and the APU bleed air had been disabled, an odour could no longer be detected. The aircraft was reapproved for operation by the technicians.
After a brief discussion, the pilots accepted the technicians’ decision because of their plausible explanation. The new cabin crew members were deliberately not made aware of the fume smell so that they remained impartial and so that, should the odour reoccur, it could be reported and described in an unbiased manner.
Once the engines had been started using a portable air starter unit and the air conditioning was running as normal on bleed air from the engines, there was no longer a fume smell.
The SUST reported the aircraft subsequently departed and was descending towards Zurich when the crew was informed by ATC they should expect a 15 minutes delay (holding). While in the first round of the holding pattern a flight attendant in the rear of the cabin noticed an odour similiar to evaporated oil and walked towards the front of the cabin noticing the odour until about mid of the cabin. She informed the purser, who in turn informed the flight deck. In the meantime the flight crew also noticed the odour, decided to declare PAN requesting to immediately continue the approach to Zurich or divert to Basel/Mulhouse (Switzerland/France) and was cleared for the approach to Zurich. The captain instructed the flight attendants to don their smoke hoods if necessary, which all but the purser complied with. The aircraft landed about 15 minutes after declaring PAN. "Very fine smoke" had become visible, however none of the passenger except the two rearmost passengers noticed the odour and haze.
While continuing the approach the captain felt it was necessary to perform the smoke,fumes or avionics smoke checklist and don his oxygen mask. Following a number of communications with ATC the smoke drill was excecuted, the captain donned his oxygen mask about 8 minutes after declaring PAN. About 13 minutes after declaring PAN the aircraft touhed down on Zurich's runway 14.
The SUST decribed the technical investigation (quoted in full):
Initial investigations into G-EUPJ were carried out the day after the serious incident. As part of these investigations, the APU was first examined and switched on. The two air conditioning packs were then put into operation using APU bleed air. When the cabin was ventilated with air conditioning pack 1, a very slight fume smell could be detected. It was not possible to reproduce the way in which the fumes developed during the serious incident.
The following day, the aircraft underwent a detailed inspection in accordance with defined procedures to determine the source of the fumes that had occurred during the serious incident. In the process, both engines were examined using a borescope; no anomalies could be identified. The engines, which had supplied the air conditioning packs with bleed air during the serious incident, could thereby be eliminated as the source of the fumes.
Indications of an oil leak were found in the APU bay in the aircraft’s tail cone, even though the APU bay had been cleaned and inspected on the previous day, prior to the APU being switched on. The leak consisted of engine oil from the APU which was dripping from the APU generator drain plug onto the APU air inlet duct in small quantities (see illustration 1).
Based on the assumption that the oil leak found in the APU was the cause of the contamination of the air conditioning system, for the further course of the investigation, the APU was neither used for the power supply nor for supplying bleed air. The two air conditioning packs were operated using an external compressor and their outlet led to the exterior to remove remaining contaminants.
Finally, a test run of the engines was carried out, during which the air conditioning packs were operated using bleed air from the engines. The test run lasted around 45 minutes and involved all possible configurations of the air conditioning system and all possible engine power settings. During the tests, all of the systems functioned without fault and there were no other noticeable indications of contamination of the cabin ventilation system.
Following the reinstallation of a flight data recorder and a cockpit voice recorder as well as other finishing work, G-EUPJ was approved for operation with a decommissioned APU. The aircraft could then be flown to London without passengers.
This article is published under license from Avherald.com. © of text by Avherald.com.
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