What happened
On 22 October 2006, a Boeing 757-204, registration G-BYAO, was operating a scheduled commercial flight from Newcastle to Larnaca. While cruising at 37,000 feet over the North Sea, the cabin manager reported a blue haze and an unusual odor in the passenger cabin, noting the condition was most prominent in the rear of the aircraft. Following the flight crew's inspection, the haze intensified, and fumes eventually reached the flight deck, prompting the pilots to declare a 'MAYDAY'.
The crew diverted to London Stansted Airport. During the descent, the haze worsened, and passengers began to feel unwell. Upon landing, the commander halted the aircraft on the taxiway and ordered an emergency evacuation. While the crew successfully opened the rear doors after significant physical effort to activate the power assist mechanisms, some passengers experienced minor abrasments during the slide descent. There were no fatalities and no injuries reported among the 160 passengers and 7 crew members.
The investigation
The AAIB investigation focused on identifying the source of the smoke and the cause of the door operation difficulties. Initial engine ground runs failed to replicate the haze, as the power settings used were insufficient to trigger the leak. Subsequent testing at higher power settings successfully identified the No 2 engine as the source. A detailed strip examination of the engine revealed oil pooling in the fan casing and streaking on the compressor blades.
Investigators also examined the aircraft's electrical systems and found a wiring error dating back to the aircraft's manufacture. This error caused the Flight Data Recorder to provide incorrect indications regarding the position of the air conditioning pack control valves. Additionally, the investigation looked into the difficulty the cabin crew experienced when attempting to open the rear exits in armed mode.
Findings
- The primary cause of the smoke was a fractured No 1 bearing floating seal ring on the low pressure shaft of the No 2 engine. This fracture allowed engine oil to escape into the compressor airflow path, where it was ingested into the bleed air system.
- The troubleshooting procedures in the Fault Isolation Manual were ineffective because they did not mandate engine ground runs at a high enough power setting to manifest the leak.
- The cabin crew struggled to open the rear doors because they were unaware that the armed mode required significantly more force to activate the door power assist and escape slide mechanisms.
Safety action
- Safety Recommendation 2009-041: It is recommended that Boeing revise the 757 Fault Isolation Manual to require higher power engine runs if initial troubleshooting fails to locate smoke sources.
- Safety Recommendation 2009-042: It is recommended that EASA ensure effective training measures are in place to familiarize cabin crews with the specific operating characteristics of aircraft exits in both normal and emergency modes.