What happened
On 1 July 1999, an MD 80, registration OY-KGZ, was taxiing from Stand H9 at London Heathrow Airport as part of a scheduled passenger flight. Shortly after starting the engines and beginning its movement, the flight crew received a report from the purser regarding thick white smoke appearing in the rear of the passenger cabin. The smoke was observed to be spreading toward the front of the aircraft at a high rate of speed.
In response to the developing situation, the commander brought the aircraft to a stop and initiated an emergency evacuation. The evacuation was carried out by the cabin crew using the front, overwing, and rear/tail exits. The process was completed in approximately one minute, and the airport's fire and rescue services, police, and ground staff arrived promptly. During the evacuation, 4 minor injuries were recorded, involving one cabin attendant and three passengers.
The investigation
Following the event, an inspection of the aircraft was performed, which showed no signs of an actual fire. The operator subsequently investigated the origin of the smoke. The investigation established that the white smoke was not caused by combustion, but rather by water that had accumulated in the coalescer bag of the left air conditioning system. This bag had detached from its support and moved into a position against a system relief valve.
Additionally, investigators identified an oil leak originating from the turbine housing of the left air pack system. Following the replacement of these faulty components, the air conditioning system was tested under operational conditions with the engines and APU running, and the system functioned correctly. The aircraft was then returned to service.
Findings
- The smoke was produced by water collecting in the left air conditioning system's coalescer bag.
- The coalescer bag had become detached from its support and was resting against a relief valve.
- An oil leak was present in the left air pack system turbine housing.