The BAe 146 aircraft had departed Brisbane, Qld on a flight to
Mackay, Qld with a carried-forward defect that required the
number-1 airconditioning pack to be used as the sole source of air
for the cabin and flight deck. That situation was permissible under
the terms of the aircraft's Minimum Equipment List (MEL), which
allowed operation of the aircraft in non-standard configurations.
The number-2 pack was not to be used because an intermittent oil
leakage in the number-4 engine was a potential source of air
contamination to airconditioning pack two.
During normal operation, bleed air from engines one and two was
fed to pack one which in turn normally supplied conditioned air to
the flight deck and cabin. Bleed air from engines three and four
was fed to pack two, which normally supplied air to the cabin only.
Additionally, bleed air from the auxiliary power unit (APU) was
used by either pack during the takeoff and landing phases or when
airconditioning was required on the ground.
The flight to Mackay was uneventful. During the approach to
land, the APU was selected as the bleed air source for pack one and
the configuration remained that way until the aircraft was parked,
the engines were shut down and the passengers disembarked.
From the time the aircraft turned off the runway, the crew was
aware of a strong oil smell coming from the air-conditioning
system. The fumes were detected in the cabin as well as the flight
deck. Because it was a short taxi distance and a busy period on the
flight deck, the crew did not have time to investigate the origin
of the contaminated air. Although the smell was generally described
as oil-like, the moderate south-east surface wind may have added to
the air contamination by directing engine exhaust fumes into the
APU air intake.
The pilot in command vacated the aircraft to get some fresh air
and a short time later he suffered headache, itchy eyes, nausea and
a bad taste. Company engineers at the Brisbane and Adelaide bases
were consulted by telephone and a decision was made to proceed with
the scheduled return flight to Brisbane using engine air one and
two as the sole source of air to pack one. As the pilot in command
was still suffering from the symptoms described above, he checked
with the first officer and confirmed that he was unaffected by the
fumes incident and requested the first officer to be the handling
pilot on the next sector.
The passengers were embarked, the doors were closed and the
engine start procedure was commenced. During the turnaround, the
airconditioning had been turned off and remained off during the
engine start. However, the cabin fan, which distributed air to the
cabin through individual louvres above each passenger seat, was on.
After starting three of the four engines the pilot in command felt
increasingly unwell and the cabin staff also became aware that they
were being affected by the fumes. The pilot in command then
cancelled the flight and later expressed concern that he had
considered attempting a flight while still feeling the effects of
the air contamination. He stated that he may have been influenced
by his desire to consult his Designated Aviation Medical Examiner
in Brisbane as soon as possible. He also noticed that he had made
simple errors during the flightdeck preparation and put those
errors down to the effect of the fumes on his thought processes.
Previous incidents have indicated that operating crews were not
aware of their impairment and the subsequent effect on their
decision making ability. The seriousness of that aspect was
reflected in the decision by the Civil Aviation Safety Authority
(CASA) to adopt a United Kingdom Air Accidents Investigation Branch
(AAIB) recommendation requiring flight crew to use oxygen masks
selected to 100 percent when there is a suspicion of flight deck or
cabin air contamination.
A Licensed Aircraft Maintenance Engineer (LAME) was dispatched
to Mackay to investigate the source of the fumes. The engineer
carried out an inspection in accordance with a CASA airworthiness
directive AD/BAe146/086, issued 30 March 2001, and British
Aerospace Systems Information Service Bulletin (ISB) 21-150. The
ISB required 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. The engineer's inspection of the
airconditioning system, engines and APU revealed no signs of oil
contamination or oil leaks. The aircraft was ferried to Brisbane
where further investigation, including an air test, confirmed that
the number-4 engine was producing fumes during the climb and the
descent and the APU was continuously producing fumes. Subsequently
the number-4 engine and the APU were replaced.
The two cabin staff received medical advice and resumed their
flying duties. Medical tests were carried out on the pilot in
command but no abnormalities were detected and he resumed flying
duties one week after the incident. The co-pilot was unaffected by
the fumes.
Particular attention has been paid to this type of problem in
Australia since July 1997 due to apparently similar incidents and
crew reaction. A number of organisations, including the ATSB, have
been conducting investigations into the subject of air quality in
BAe146 aircraft. Evidence from previous incidents of air system
contamination on this type of aircraft has indicated that the fumes
are associated with engine or APU oil contamination of the
airconditioning system. As a result, operators have incorporated
various modifications to the cabin air system, APU and engines.
They have also introduced improved maintenance practises to further
address the issue. However that action has not completely solved
the problem. The air supplied to the air conditioning packs is
protected from contamination by oil seals in the engines and APU. A
technical defect arising in one of these seals can result in oil
entering the cabin air conditioning system with the first signal of
the defect being an awareness of fumes by the members of the crew.
The difficulty of identifying the origin of the contamination is
exacerbated by the often intermittent nature of the fume
events.
