TSB Raises Bar On
FRANCES FIORINO/NEW YORK
The Transportation Safety Board of
Canada last week released the fourth set of safety recommendations--these
focusing on material flammability standards--stemming from its ongoing
probe of the Sept. 2, 1998, crash of Swissair Flight SR111 into the
Atlantic Ocean off Peggy's Cove, Nova Scotia.
The investigation to find the cause of the inflight fire that is
suspected of downing the MD-11, killing 215 passengers and 14 crew
onboard, is "by far and away the most complex and challenging" one faced
by the board, said TSB Chair Benoit Bouchard. It has proven to be "a
puzzle of outstanding magnitude." Since initiating the probe in 1998, the
board issued recommendations related to firefighting measures, power
provided to flight recorders and recording capacity, thermal acoustical
blankets and flammability test criteria ( AW&ST Dec. 11, 2000,
p. 85; Nov. 23, 1998, p. 41).
The latest set of recommendations are "intended to address deficiencies
in regulatory requirements and industry standards and practices which
compromise safety." Specifically, they are related to materials used in
the manufacture of aircraft, the testing of wiring and the potential for
systems to exacerbate an inflight fire:
Material flammability standards (Recommendation A01-02). For the
pressurized portion of an aircraft, flammability standards for material
used in the manufacture of any aeronautical product be revised, based on
realistic ignition scenarios, to prevent the use of any material that
sustains or propagates a fire.
VIC GERDEN, SWISSAIR 111 investigator in charge, said no
material should be used if it sustains or propagates fire in the operating
environment, and that "an airplane should not crash as a result of one
ignition source." He points out the board recommended removal of thermal
acoustical blanket material, identified earlier in the probe as a factor
in the SR111 fire. He adds that other materials, such as elastomeric
substances, which are not required to pass rigorous certification tests,
were in the aircraft. Indications from ongoing analysis are that such
materials burned off earlier and likely augmented propagation of that
- Material flammability test requirements for aircraft wiring
(A01-03). A certification test regime be mandated that evaluates
aircraft electrical wire failure characteristics under realistic
operating conditions and against specified performance criteria, with
the goal of mitigating risk of ignition.
Gerden said aircraft wiring testing should be far more stringent as
wiring can be an active ignition source. "We know that fire could have
been ignited by an electrical arc from a wire, and here's a sobering
fact--an aircraft of this type contains about 250 km. of electric wire."
The only test currently mandated for certification is the "60-sec.
Bunsen burner" that is performed on a single, unpowered wire and
designed to determine if insulation material will burn and for how long.
- System evaluation: fire-hardening considerations (A01-04). As a
prerequisite to certification, all aircraft systems in the pressurized
portion of an aircraft, including subsystems, components, and
connections, be evaluated to ensure that those systems, whose failure
could exacerbate a fire in progress, are designed to mitigate the risk
of fire-induced failures.
Bouchard said all aircraft systems should be evaluated in terms of
impact on inflight fire. If it is determined they would exacerbate a fire,
redesign should be considered.
Gerden said many parts of the same system could have dissimilar
properties and some parts may fail before others. Most of the oxygen lines
in the MD-11 are made of stainless steel but have aluminum caps/fittings.
A failure disconnecting the lines could lead to a large amount of oxygen
propagating a fire.
When asked about industry costs involved in implementing the
recommendations, Gerden said it was "hard to put a price tag on it at this
point," but estimated a world fleet cost of $1 billion for removal of
mylar material. But first, he said, "an assessment would have to be done,
and that is a function of the regulatory authority."
He said there is still investigative work ahead, and the TSB's final
report on the crash of Swissair Flight SR111 is expected "sometime next
© September 3, 2001 The McGraw-Hill Companies
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