While on descent into Melbourne, the crew of a British Aerospace
146 (BAe 146) freighter reported that they began to smell oil
fumes. The descent was being conducted at an engine power setting
of between 60% and 70% N2, with all four engines supplying bleed
air. Both environment control system (air conditioning) packs were
selected ON. The crew, who were the only occupants of the aircraft,
consisted of the pilot in command, the co-pilot, and a
supernumerary pilot. The pilot in command was the handling pilot
for the sector.
The pilot in command advised that, following the onset of the
fumes, he had experienced difficulty in concentrating on the
operation of the aircraft, and had suffered from a loss of
situational awareness. By the time the aircraft had reached an
altitude of approximately 2,000 ft, his control inputs had become
jerky and he began suffering vertigo. He relinquished control of
the aircraft to the co-pilot, who continued with the approach and
landing. The supernumerary pilot advised that he had felt nauseous.
The pilot in command advised that because no smoke or mist was
present within the cockpit, he did not consider it necessary to
follow the smoke-removal checklist. He also advised that the crew
did not consider the use of crew oxygen masks was necessary in the
situation.
After boarding the flight in Sydney, the supernumerary pilot had
examined the aircraft maintenance release and noted a deferred
defect concerning oil residue at the number two air conditioning
pack inlet, resulting from an oil leak from the number four engine.
This maintenance release entry was dated 17 June 1997. Maintenance
trouble-shooting had isolated the problem to a failing oil seal
within the number four engine. The aircraft had been cleared for
further flight without any operational restrictions being noted,
and the defect was listed for rectification at company
convenience.
On experiencing the fumes during the descent into Melbourne, the
supernumerary pilot recalled that he had noted a defect concerning
the number two air conditioning system, and rechecked the
maintenance log to determine which bleed air system may have been
contributing to the source of contamination.
After shutdown at Melbourne, the crew vacated the aircraft.
Following exposure to fresh air for about 30 minutes, the effects
of the oil fumes dissipated. As a result, the crew did not consider
it necessary to seek medical advice before continuing the scheduled
flights. This decision was reinforced by the fact that the co-pilot
had not reported being affected by the fumes. The crew further
advised that because the technical log already contained an entry
regarding the number four engine, and because Maintenance were
aware of the problem, another entry regarding the same problem was
unnecessary. They elected to continue the remaining scheduled
flight sectors with the number four-engine bleed air system turned
off, in accordance with the provisions of the master minimum
equipment list (MMEL). The remainder of their tour of duty was
completed without incident.
Some 6 hours after the incident, and for the next 10 days, the
pilot in command suffered from severe headaches characterised by
the feeling of a strong pressure on the top of the head. This
diminished over time; however, he did report having balance
problems while attempting to rise in a darkened room at night, and
also reported that he had experienced increased headaches and
vertigo while travelling. The supernumerary pilot reported reduced
but similar symptoms. The co-pilot did not report having been
affected by the fumes.
Following this occurrence, the pilot in command submitted an air
safety incident report, and also advised the operator of the
circumstances of the occurrence. The operator applied minimum
equipment list (MEL) 20-50-1 on 14 July 1997, prohibiting the use
of the number two air conditioning pack, thus preventing oil
contamination of the air conditioning system by the number four
engine. The engine was subsequently replaced on 16 July 1997.
The BAe146 aircraft is a high-wing, four-engine jet transport,
which first entered service in 1983. An auxiliary power unit (APU)
is mounted in the tail, along with two environment control system
packs. High temperature bleed air is supplied by the compressor
section of each engine and the APU. The bleed air is then passed
through the environment control system packs, where it is
conditioned before distribution into the aircraft cabin.
During the course of the investigation, a number of flight and
cabin crew members, employed by various Australian operators on
BAe146 type aircraft, reported to the Bureau that they and others
were experiencing a number of health problems. The crew members
reported that they were either off work permanently, on prolonged
sick leave, or in receipt of medical certificates that precluded
them from undertaking normal crew duties on the aircraft. The crew
members reported a variety of differing physical reactions arising
from their perceived exposure to fume contamination, the most
common being sore eyes, nose and throat; nausea; tiredness; and
headache. The more disabling reactions reported include any of the
above symptoms plus any of the following: dizziness, balance
problems, extreme tiredness, extreme reaction to all oil-based
products (including plastics and cosmetics), feelings of
intoxication, slurred speech, inability to walk straight, skin
rash, itchiness and blotching.
The investigation found that smoke and fume contamination of
cabin air is neither a new phenomenon nor a particularly rare event
and that over time, it has been experienced in many aircraft types.
The Australian experience has found that many complaints have been
recorded against the BAe146 type. As a result, Australian domestic
operators of the BAe146 have established internal reporting systems
whereby reports of odours are submitted by crews on specifically
designed forms that are collated and analysed, as a means of
establishing the extent of the problem.
In August 1997, the operator published a Notice to Pilots
(NOTOP) 37/97 concerning alleged air conditioning contamination on
BAe146 and Avro RJ aircraft types. The NOTOP stated that it was not
a new phenomenon, and that all aircraft air conditioning systems
would induce foreign odours from oil or fuel on occasions during
routine operations. Attached to the NOTOP was a schedule to be used
by flight crew to determine the source of air conditioning
contamination. The schedule required flight crews to operate BAe146
aircraft on a series of sectors with various air supply and air
conditioning pack selections to identify the source of
contamination.
One operator supplied air-sampling kits on board the aircraft,
and medical checks were offered when crew complained of exposure to
cabin air contamination. The Bureau of Air Safety Investigation was
unable to determine if details of all reported odour occurrences
were entered into aircraft maintenance logs. Other reports were
made directly to medical personnel, some to employee
representatives, and some were made verbally to the Bureau. Some
reporters advised that they would not report to their employers
because they feared reprisals.
Visual descriptors of the contamination included "smoke",
"fumes", "oil mist", and "fog". Smell descriptors included "acrid",
"vomit", and "smelly socks". The investigation labelled all
described forms of contamination as odours. It was found that the
odour reports defined two distinct modes: one that could be
associated with oil fumes, and another that could be associated
with a stale air environment. Identified causes of foul air supply
included engine and APU oil seal leakage, hydraulic oil leaks,
electrical component overheating, and problems associated with food
heating facilities in galleys.
BAe146 operators approached the manufacturers of the aircraft,
engines and APU. As a result, a series of tests and trials were
designed to ascertain whether the aircraft met all the relevant
certification requirements, and whether modifications were required
to alleviate the cabin air quality problems being experienced from
time to time.
As a result of testing and research, operators undertook a
number of corrective maintenance actions and modifications to BAe
146 aircraft in the Australian fleet in an attempt to mitigate
odour occurrences within the cabin. These actions included more
frequent air filter cleaning, replacement of APUs with an
alternative unit, modifications to APUs to improve ventilation in
and around the unit and associated air intakes, assessment of
filter life, air duct cleaning, and the replacement of ducts likely
to trap oily deposits. The air conditioning packs were also "burnt
out" on a daily basis. This procedure was intended to increase pack
operating temperatures in an attempt to burn off any remaining oil
residues within the air conditioning system, but was discontinued
by Australian operators because it apparently caused deterioration
of the packs. There was also an increase in the frequency of engine
oil seal inspections and replacement.
The Bureau of Air Safety Investigation is particularly concerned
about the potential for further BAe146 flight and cabin crew to
become incapacitated during flight due to exposure to odours being
introduced into the aircraft cabin environment. In this occurrence,
two of the three flight crew members on board the aircraft suffered
from symptoms that prevented them from properly carrying out their
assigned duties. The introduction of fumes and odours into the
cabin environment following an engine defect constitutes a possible
safety deficiency that should be addressed by the regulatory
authority, in accordance with its statutory responsibility to
monitor the continued airworthiness of aircraft.
The implications of long-term exposure to cabin air
contamination for the health of passengers and crew requires
further examination, together with the development and
implementation of suitable counter-measures. The competent
authority to co-ordinate such activities is the regulatory
authority.
