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 air conditioning 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 take-off 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 air conditioning 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 air conditioning 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 air conditioning 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 air conditioning system was operating under the highest design load condition with several components running at high temperature.
