What happened
Between 12 and 23 November 2004, a Boeing 757-236, registration G-BPEE, experienced a series of flights characterized by the presence of fumes in the cockpit and cabin.
On the first occasion, flying from London Heathrow to Nice, the crew and passengers detected odors. During the return leg, the pilot experienced a burst of contaminated air and felt physically unwell, necessitating the use of oxygen masks.
On 1 and 16 November, a second flight to Stockholm Arlanda saw the crew encounter a "warm aromatic" smell. During this flight, the crew and cabin staff reported physical symptoms including sore throats, headaches, nausea, and a sensation of being "spaced."
A third occurrence took place on 23 November during a flight to Milan Malpensa, where the smell returned during the descent and was mitigated by turning off the left air-conditioning pack and bleed-air sources.
The investigation
The AAIB conducted several investigations into these events. During troubleshooting, engineers identified evidence of burnt hydraulic fluid on the exterior of a bleed air duct on the left engine. Chemical analysis of swabs from inside this duct suggested that hydraulic fluid had migrated into the air supply path.
While a leak was found in a thrust reverser hydraulic pipe located above this duct, the investigators noted that the pipes are enclosed in shrouds designed to contain leaks. Furthermore, the crew descriptions of the odor—ranging from "warm sweet" to "oily-sewage"—did not align perfectly with the typical acrid smell of hydraulic fluid.
Engine inspections and chemical analysis of the engines also revealed traces of engine oil in the compressor swabs, though no definitive evidence of overfilling or a primary oil leak source was established during the strip examination of the left engine.
Findings
- The presence of hydraulic fluid migration into the HP2 bleed air duct was confirmed, though it was unclear if the volume was sufficient to cause the reported symptoms.
- Traces of engine oil were identified in the compressor components, but no specific leak source or overfilling error was identified for this specific aircraft.
- The varying descriptions of the odor by the crew made it difficult to definitively attribute the fumes to a single substance.