The British Aerospace 146-100A (BAe 146) was being prepared for a regular public transport service from Perth to Newman, WA. As the copilot boarded the aircraft to conduct pre-flight checks he detected strong fumes in the cabin and the flight deck. He noted that the auxiliary power unit (APU) was supplying bleed air to one of the aircraft's two air conditioning packs that in turn supplied conditioned air to the flight deck and cabin. In an attempt to clear the fumes, he directed the bleed air supply to the alternate pack.
Bleed air from the APU was generally used when air conditioning was required during ground operations or during the take-off and landing phases. During flight, the air conditioning packs receive bleed air from the engines.
As the copilot continued the pre-flight checks, he noticed the cabin fumes becoming stronger and so shut down the air conditioning pack and opened the flight deck windows.
Maintenance engineers were requested to investigate the source of the fumes and subsequently discovered an oil leak in the APU generator drive adaptor pad. Rectification work, including the replacement of a carbon seal, was carried out 11 days later, on 13 December. To enable the aircraft to continue in service on the day of the incident, the APU was isolated from the air conditioning system in accordance with the terms of the aircraft's Minimum Equipment List (MEL) that permitted operation of the aircraft in non-standard configurations. The operator reported that the maintenance engineers then addressed the defect in accordance with the Civil Aviation Safety Authority (CASA) airworthiness directive AD/BAe146/86, effective 3 April 2001, and the British Aerospace Systems Inspection Service Bulletin (ISB) 21-150. That ISB called for certain actions to be performed whenever a cabin air quality problem was identified, which was suspected of being associated with oil contamination of the air supply from the air conditioning packs. No oil contamination was found. The engineers then operated both packs using bleed air from engines 1 and 4 until they were satisfied that there were no fumes and the aircraft was then released for service.
The copilot had been exposed to the fumes for approximately 30 minutes. The two cabin crew, who boarded the aircraft shortly after the copilot, were exposed to the fumes for approximately 20 minutes. All three were eventually affected by the fumes, became unwell, and were removed from flight duty. In accordance with company standard practice they underwent medical examinations. The pilot in command was exposed to the fumes for less than 5 minutes and was not affected. Impaired performance due to the inhalation of contaminated air is considered a potential threat to flight safety. For that reason, company procedures emphasise the importance of flight crew donning oxygen masks if poor air quality is suspected during flight.
The pilot in command and a replacement crew subsequently departed in the same aircraft for the flight to Newman. The cabin crew reported a slight smell of fumes toward the rear of the aircraft during the first sector. On the return sector, both cabin crew reported feeling unwell, with symptoms consistent with fumes inhalation.
Follow-up inspections of the air conditioning system, engines and APU were carried out in accordance with the CASA airworthiness directive and no contamination was evident. On 6 December, the operating crew indicated that a smell was apparent and it appeared to be consistent with the operation of the APU. As the APU was still isolated, engineers doubted that it could be contaminating the air conditioning system. All four engines and the regenerative ducts were again checked, with no contamination evident. Follow up inspections were scheduled in accordance with the ISB.
A further cabin air quality event occurred on 12 December, when the flight deck crew detected fumes shortly after departure. The flight crew proceeded to identify the source of the fumes using a contamination source location schedule. That schedule involved selecting different combinations of engine air and air conditioning packs. The fumes were traced to the number 3 engine, which was isolated, and the flight continued as planned. Subsequent inspection revealed oil wetness in the number 3 engine high-pressure compressor; the result of a worn number 1 bearing seal. Trend monitoring had not indicated abnormal oil consumption for that engine. The engine was replaced and airworthiness directive AD/BAe146/86 was complied with. No further contamination was evident and fumes were not reported during subsequent flights.
Evidence from previous incidents of air system contamination on this aircraft type had indicated that fume events were often intermittent in nature and were associated with engine or APU oil contamination of the air conditioning system. The air supplied to the air conditioning packs was protected from contamination by oil seals in the engines and APU. A defect in one of those seals could result in oil entering the cabin air conditioning system, with the first sign of the defect being an awareness of fumes by passengers or crew members.
The investigation of cabin fumes incidents on BAe 146 aircraft has typically been characterised by a difficulty in precisely locating the original source of the oil leak that led to the creation of the fumes. That has been especially so if there was more than one engine/APU leak combination. The failure of oil seals has been a common factor in the majority of those incidents.