The ATSB did not conduct a technical investigation of this
incident. The report has been compiled with the aid of information
provided by the airline operator.
While en route from Sydney to Melbourne at flight level (FL)
410, fumes were detected in the flight deck and an aft toilet smoke
detector was activated by smoke haze in the rear of the aircraft.
The crew carried out the appropriate non-normal procedures and
diverted the aircraft to Canberra as a precautionary measure.
During the descent the engines were at idle thrust and the fumes
decreased in intensity.
Engineering staff carried out a series of checks on the aft
galley and the air conditioning, electrical and powerplant systems.
No defects were found and the aircraft was then ferried to Sydney
for further checks. No fumes were evident during the flight at
FL230 nor during the subsequent engine ground runs. The aircraft
was returned to service and operated for eight sectors without
incident.
Two days later, the fumes were again detected as the aircraft
climbed through FL410 en route from Sydney to Melbourne. The flight
crew carried out the non-normal checklist for "Smoke or Fumes Air
Conditioning" and the aircraft was turned back to Sydney. Following
that incident, engineering staff carried out inspections of the
pneumatic ducting and the airconditioning system. No evidence of
oil contamination was found in the pneumatic system. Hydraulic
reservoir pressurisation modules and recirculation filters were
replaced and an assessment flight was then conducted. The takeoff
and climb phases of flight were uneventful but as the aircraft was
levelled out at FL416, an acrid odour became apparent in the cabin
and flight deck. An isolation procedure was initiated which traced
the source of the odour to the right pneumatic distribution system
and the right airconditioning system. Following that flight, the
right engine was changed.
During a second assessment flight, the odour re-occurred in the
cabin as the aircraft was flown above FL410. By using a sequence of
bleed air conditions, in which each pack was operated independently
and from each engine bleed system in turn, the source of the odour
was isolated to the right air conditioning pack system. A
subsequent ultraviolet light inspection of the pneumatic ducting
indicated that the pneumatic ducting was free of engine and
hydraulic oil contamination.
Various components of the right airconditioning system were
removed and replaced including the air cycle machine (ACM), water
separator, condenser, reheater and primary and secondary heat
exchangers. An inspection of those components revealed a black
deposit on the ACM compressor wheel and 500 mL of brown fluid in
the right secondary heat exchanger. The secondary heat exchanger
and downstream components were also found to emit the same odour as
that noted during the assessment flights. The secondary heat
exchanger had undergone a complete overhaul in July 2000, at a
contracted repair facility in the United States, before being
returned to the operator. The contractor's internal process review
revealed that there were differing processing requirements in
regard to the coating applied to the exchanger for corrosion
protection. During a strip and repaint of the exchanger, the
protective coating was baked at a significantly lower temperature
than if the exchanger had been completely re-cored.
The right airconditioning components were replaced and a further
assessment flight was conducted. No odours were evident at any
altitude or operating condition during the flight. The aircraft was
then returned to service and subsequently operated without
incident.
A sample of the brown fluid recovered from the secondary heat
exchanger was independently analysed using infra-red spectroscopy.
The results of the analysis indicated that the primary contaminant
was sodium polyacrylate, a water treatment chemical. Material
Safety Data Sheets for products containing that chemical indicated
that inhalation of the compound in vapour/mist form may cause
irritation to mucus membranes. Further analysis using gas
chromatography/mass spectrometry did not show the presence of
sodium polyacrylate but indicated a range of numerous phenol-based
compounds that would produce offensive odours. The discrepancy
between the results of the two sets of tests could not be
explained. A consultant occupational hygienist, experienced in
cabin air quality testing, was unable to determine the potential
for the contaminants exiting the air conditioning system to cause
harm to either the passengers or the crew on the aircraft.
Maintenance records indicated that the secondary heat exchanger
had been installed in the aircraft on 18 September 2000. Following
installation, the aircraft flew 30 sectors before the fumes
incident on 30 September 2000. Data was not available on the levels
flown on those sectors but the operator indicated that it was
probable that they were flown below FL410. Following the
engineering work after the first incident, the aircraft was
released back to line and operated eight domestic and international
sectors without any cabin air quality problems becoming evident.
The levels flown ranged from FL290 to FL390. The second fumes
incident on 02 October 2000, occurred when the aircraft climbed to
FL410. Between FL410 and FL431 (the maximum certified altitude for
the aircraft) the airconditioning system was operating under the
highest design load condition with several components running at
high temperature.