Aviation Investigation Report A98H0003
- 220.127.116.11 - Reports of Unusual Odours
- 18.104.22.168 - Procedures for Reporting and Recording Abnormal Conditions
22.214.171.124 Reports of Unusual Odours (STI1-121)
On the first flight following a scheduled maintenance inspection, approximately three weeks prior to the SR 111 accident, when HB-IWF was operating as SR 178, an unidentified smell was detected within the aircraft cabin in the vicinity of the L1 door. This location is below an area where some of the heat damage was observed on the SR 111 aircraft wreckage. Various descriptions provided by the aircraft crew included smells similar to an over-heated electrical appliance or an unfamiliar type of gas or chemical. The smell incident was verbally reported to a maintenance engineer immediately following the flight; his inspection of the area did not reveal any discrepancy. Subsequent explanations included a possible residue of an insecticide that had been administered during the maintenance inspection prior to flight or fumes from the cargo compartment. The cargo manifest indicates that some solvents were being carried as dangerous goods in the forward cargo hold during that flight, although no cargo spills or loss claims were reported. The source of this smell on SR 178, which occurred 23 days prior to the accident flight, was not identified. There were no further reports of any recurrence of such a smell condition on the 50 subsequent flights of HB-IWF, and there is no reason to link the events of flight SR 178 to the accident flight.
On two separate occasions, a "burnt" or "burning" odour was detected on another Swissair MD-11 aircraft, HB-IWH. On 11 July 1998, a passenger on board HB-IWH operating as SR 111 detected a burnt odour. The smell was detected in flight after the meal service in the area of passenger seat 14H. On 18 August 1998, a passenger on board SR 264, aircraft HB-IWH, detected an unusual smell described as a burnt odour. The smell was detected prior to take-off in the area of seat 18J, mid-cabin. The M/C investigated, but did not smell anything. He reported this to the flight crew.
Because the same aircraft (HB-IWH) was used for both flights and because on each flight, passengers reported a burnt odour within an area spanning four passenger-seat rows (passenger seat 14H and 18J respectively), investigators assessed the possibility of potential links between the July 1998 and the August 1998 flights of HB-IWH. However, because there are no records or other information indicating the source of the burnt odour on the August 1998 flight and because the passenger from the July 1998 flight only reported the burning smell to the TSB several months after the flight, it was not possible to draw any link between the two events.
126.96.36.199 Procedures for Reporting and Recording Abnormal Conditions (STI1-122)
A search of the Swissair MD-11 Cabin Flight Report database for additional information concerning abnormal smells on board HB-IWF and other MD-11 aircraft since 1997 resulted in only one other report. At the time of the occurrence, the procedures for cabin crew to record abnormal conditions did not clearly state when a written report (Cabin Flight Report) was required. Also, the procedures for flight crew regarding the recording of abnormal conditions reported to them by cabin crew allowed for discretion by the flight crew. Such abnormal conditions would have been recorded, at the captain's discretion, in the aircraft logbook. A logbook entry would have resulted in a subsequent maintenance action. Because no such entry was recorded in the logbook, an opportunity to troubleshoot the source of the unusual odours was lost.
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