Wednesday, August 04, 1999

Swissair crew reported smells on earlier flight

Pilots of doomed plane complained about dense smoke

Associated Press

ZURICH - Less than a month before a Swissair jet crashed into the Atlantic Ocean off the coast of Nova Scotia, killing all 229 people aboard, crew members on the same plane reported strange smells in the cabin, a Swissair official said yesterday. 

A steward on the MD-11 noticed an odour shortly after the plane took off from Zurich bound for Hong Kong on Aug. 10. The smell became stronger during the flight, prompting the chief steward to file a report to the airline, said Urs Peter Naef, spokesman for Swissair.

No problems were found and the report was never published.

Only 25 days later, the same plane took off from New York enroute to Geneva. The pilots mentioned a strange smell and then complained of dense smoke.

Flight 111 was headed for an emergency landing in Halifax, but fell short and plunged into the sea near Peggy's Cove, N.S.

The crew's original report was passed on to Canadian investigators after the crash, said Mr. Naef, confirming an article in the Swiss magazine Facts.

Investigators still have not identified the cause of the fire that sent the smoke into the cockpit, although attention has focused on electrical-wiring problems. The odour report is one of millions of documents investigators and Swissair staff are analyzing, the airline said.

Crew members from the previous Hong Kong flight were flown to Halifax for questioning by the Canadian Transportation Safety Board and given different sample odours to smell, including those of burning wires but there was nothing conclusive and the report was shelved.

Beatrice Tschanz, spokeswoman for Swissair, said the report is not believed to be connected to the crash. "This report was investigated, and it was proven that it had nothing to do with the cause of the crash," she said.

Subsequent inspections of other MD-11s found some had cracked and chafed wiring around forward cabin doors and the wall separating the cockpit from the forward galley.

Swissair faces a total of $16-billion (US) in claims from families of U.S. victims suing on grounds of gross negligence. The company said it has reached out-of-court settlements with relatives of five victims in France.

A pre-trial conference in Philadelphia later this week will sort out procedural technicalities of the suits against Swissair and other defendants, the airline said.

The other defendants include Boeing, which owns the company that manufactured the plane; Delta Air Lines, which had a ticket-sharing deal with Swissair; and Inflight Technologies, which provided the plane's electronic entertainment system.

Philippe Bruggisser, chief executive of the airline's parent company SAirGroup, has said Swissair has already paid about $135,000 (US) in compensation for each victim.

MD-11 Cabin Interior

If it ain't broke, don't fix it?

Reading this report you cannot help but reflect upon the fact that also "less than a month" before sr111 crashed, that MD11 had its bus-tie sensing relay changed. Because of a fire that had occurred in Bangkok on 03 Aug Swissair maintenance decided to swap-out all the MD-11 bus-tie relays on 4 Aug 98.

The technician installing the new relay in HB-IWF made an error and when it was powered up it shorted out. A short in Kapton wiring is no small thing. Faults can be induced both up and downstream in wiring bundles and components. You have to wonder just how extensively the associated wiring was checked out after the short circuit. You can read the original Swissair version here and here. It's difficult to be persuaded that the installation fault was simply rectified and all was then guaranteed to be as new.

If someone reports a bad smell, just how do you go about checking that out? Do you think to yourself  "Well they wouldn't have reported it if there hadn't been a significant odour? We'd better look until we find something".  Do you then tear the lining out and really go for it with conviction. Or do you just power up the systems, turn off the circulation and do a sniff check? If you don't smell anything it's as easy as a "No fault found" write-up. Engineering just cannot justify chasing will-o-the-wisps when the aircraft isn't scheduled for any maintenance down-time.

You have to wonder what the McDD MD11 maintenance manual says specifically about chasing down reported smells. What's the betting that it doesn't say anything?

Why would you get a bad smell six days after the bus-tie relay swap-out and then why would it go away of its own accord? Aircraft in flight are subjected to a myriad of forces. There's the high-frequency vibration of its aerodynamic passage (as varied by the engines' resonant notes). You can see that by simply holding a glass of liquid and allowing it to gently touch the window. You'll see concentric ripples of small amplitude all very close together. That's the vibration that causes wire chafing over very long periods (it contributes to the wiring insulation's aging characteristics). If you then hit turbulence you'll have some very low freq but high amplitude vibration. That, together with fuselage and wing flexing, can cause whole wire bundles to reposition (albeit just a few mms). And of course you've got the additional "turbulence" of landing forces as transmitted through the airframe. You also have the operation of systems and the opening and closure of doors that can impinge upon wiring bundles. You only need to achieve a conjunction (i.e. make & break) over a few millimetres between insulation-damaged wires in order to initiate arcing. Once the initial smelly damage has occurred, vibration may then move the wires apart and the arcing may cease. However damage has been done and the next time that they are moved back into close conjunction the process starts anew (and the damage spreads). Because of the forced air circulation both above and beneath the cabin lining,  localising it is a real task requiring great thoroughness. I'd like to know precisely what the response was to this report of smoke. Was it nominal or was it very thorough? How thorough is very thorough? Is that sufficiently thorough? Is not a bad smell a sufficient prompt for great thoroughness. Obviously it would be now (but was it ever thus?). Read an example here of just how you can be caught out. It was sheer Luck in this instance that they found this fire damage before the aircraft flew again.

What has the Boeing approach been to this question of reported smells? Is it now changed? When did it change? Does it accord sufficient priority to the reports of "bad smells". Should Flight attendants be expected to start ripping into cabin linings in flight after the flight-crew secures the air-con circulation? Or would that be too upsetting for the passengers?

But we needn't concern ourselves because: