Incidents Overview
In November 2004, a Boeing 757-236 (registration G-BPEE) operated by a public transport carrier encountered several incidents of fumes in the cockpit and cabin over three separate flights. The events occurred on 12, 16, and 23 November, with additional reported occurrences on 9 December 2004 and 16 January 2005. No definitive cause was identified.
Incident of 12 November 2004
This flight was the aircraft's first following a major maintenance check. During the outbound sector from London Heathrow to Nice, the flight crew detected fumes in the cockpit, and passengers in the forward cabin and cabin crew in the rear galley also reported smelling fumes. After landing, the crew contacted Flight Operations and decided to operate the return sector. After engine start, a "strong but short burst" of "contaminated air" was smelled when the left air-conditioning pack was selected on, but it quickly cleared. During the flight, four or five further "sharp bursts" occurred, associated with the left pack tripping on and off. During descent into London Heathrow, a stronger, more persistent smell prompted the commander to consider using oxygen, feeling "a bit spacey". The Cabin Services Director confirmed the odour, and both crew donned oxygen masks before declaring a PAN and performing QRH drills. After landing, a fireman confirmed the odour. The captain reported feeling unwell for three days post-flight and consulted a doctor.
Incident of 16 November 2004
This was the aircraft's first flight since the previous incident. During boarding for a flight to Stockholm Arlanda, a strong smell was noted in the cabin (APU not running). On takeoff, a "warm aromatic" smell appeared in the cockpit. The QRH procedure for smoke/fumes was actioned; the right pack was selected off, clearing the air. In cruise, odours returned, prompting oxygen mask use. The Cabin Services Director described the odour as a "warm sweet smell, but slightly burnt". The left pack was turned off and right pack on; the smell cleared. About 80 minutes into the flight, the Purser at Door 4 reported sore throats with her colleague; the air seemed irritant at the rear galley. During descent, the co-pilot felt a "buzzy head and body", and at 3,000 feet an "oily-sewage" smell was noted. At 2,000 feet, the captain felt "slightly spaced" and had concentration difficulty. After landing, crew visited a paramedic and then a doctor, reporting headaches, sore throat, coughing, nausea, burning sensation in lungs, and a "slightly spaced" feeling. They were cleared to return to the UK.
Incident of 23 November 2004
On a flight to Milan Malpensa, an unusual background smell confined to the cockpit was noted, coming and going during descent. On the return sector, no smells were noted during climb and cruise, but the smell returned more strongly in descent. Selecting the left pack and bleed-air off caused dissipation; the smell returned when restored for approach. Cross-feeding the left pack from the right bleed during taxi did not dissipate it.
Engineering Investigation
After the 12 November incident, standard troubleshooting included engine oil checks (acceptable levels), fan blade inspection, APU inspection (oily area but no leak), and finding hydraulic fluid seepage at the rudder base. Engine ground runs produced no unusual smells. The left pack control valve was replaced.
Following the 16 November incident, a slight odour was detected when the left pack was supplied by the right engine. The right engine oil pump assembly was replaced. Boroscope inspections and chemical analysis of swabs from the right engine compressor identified traces of Mobil Jet II engine oil. Burnt hydraulic fluid was found on the exterior of a bleed air duct on the left engine (Part Number 312N5306-1), which supplies HP2 bleed air.
Related Findings
The AAIB also investigated a prior fume event on another Boeing 757 (G-CPER) from the same operator. That investigation found that engine oil servicing was not consistently performed per the Aircraft Maintenance Manual (AMM), potentially leading to overfilling and oil contamination of the bleed air. The operator subsequently amended procedures and provided training, resulting in a significant reduction in reported air contamination events. However, for G-BPEE, the investigations did not definitively establish the source of the fumes.