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 airconditioning 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 airconditioning
was required during ground operations or during the takeoff and
landing phases. During flight, the airconditioning 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 airconditioning
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 airconditioning
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 airconditioning
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 airconditioning 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 airconditioning 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 airconditioning
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 airconditioning system. The air supplied to
the airconditioning 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 airconditioning 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.
