Wednesday, August 04, 1999
Swissair crew reported smells on earlier flight
Pilots of doomed plane complained about dense smoke
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
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
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
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.
Zurich, during the installation of the new DC tie bus sensing
relay in the sr111 aircraft, HB-IWF, the mechanic discovered
that he had incorrectly installed the part after a short circuit
- not a fire - occurred. The DC tie bus sensing relay was
then installed correctly and subsequent function controls
confirmed that the relay functioned properly.
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
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.
|In order to re-dispatch the aircraft as
soon as possible in accordance with the Minimum Equipment
List (MEL), the maintenance crew manually closed the exhaust
valve and fitted a 'shorting link' to remove the EICAS message.
However, despite this action the warning message persisted.
As part of the ensuing troubleshooting process the valve,
in addition to the ECS card and an associated relay, were
all replaced; however the problem persisted. By this time
crew duty time limitations had intervened and so the aircraft
remained overnight at LHR, enabling the maintenance crew to
further investigate the problem. Wiring continuity checks
were carried out and eventually an area of damaged wires was
found close to, and associated with, the exhaust valve. These
damaged wires had been hidden from view by having been previously
installed, incorrectly, beneath the bilge thermal insulation
blanket and next to the fuselage skin. It was evident that
a localised fire had occurred between the outer film of the
blanket and the fuselage structure.
(VH-OJD QANTAS B747-400)
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:
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.