NTSB DETERMINES CAUSE OF GROUND FIRE ABOARD CARGO AIRPLANE IN SAN FRANCISCO

[NTSB Press Releases <NTSBPressReleases@xxxxxxxx>]

Title: NTSB DETERMINES CAUSE OF GROUND FIRE ABOARD CARGO AIRPLANE IN SAN FRANCISCO

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                      NTSB PRESS RELEASE
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National Transportation Safety Board
Washington, DC 20594

FOR IMMEDIATE RELEASE: June 30, 2009
SB-09-32

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NTSB DETERMINES CAUSE OF GROUND FIRE ABOARD CARGO AIRPLANE
IN SAN FRANCISCO

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WASHINGTON, DC - The National Transportation Safety Board
has determined that the probable cause of a ground fire that
caused extensive damage to a cargo airplane last year was
due to the design of oxygen system hoses and the lack of
positive separation between electrical wiring and
electrically conductive oxygen system components. The
Federal Aviation Administration's (FAA) failure to require
the installation of new oxygen system hoses to remedy a
safety issue previously identified by Boeing was cited as a
contributing factor.

At 10:15 PM PT, on June 28, 2008, at San Francisco
International Airport, an ABX Air Boeing 767 cargo airplane
experienced a ground fire just aft of the cockpit area
before engine startup. The cargo airplane was operating as
flight 1611 and was destined for Wilmington, Ohio. Airport
rescue and firefighting (ARFF) personnel extinguished the
fire, which had burned holes through the crown of the
aircraft in the forward galley area, in a timely manner. The
captain and first officer, the only two aboard the aircraft
at the time of the fire, evacuated the airplane through the
cockpit windows and were not injured. The fire started in
the supernumerary compartment, which is located between the
cockpit and the main deck cargo compartment. 

Crew descriptions about what was heard when the fire
started, combined with Safety Board testing, revealed that
the ignition source had to be within the oxygen hose. The
Safety Board's investigation determined that a short circuit
to the supplemental oxygen system reached the oxygen hose.
The design of the hose included an internal spring, which
could be heated by the inadvertent application of electrical
current, causing the plastic hose to ignite. Safety Board
testing found that the hose design brought together the
three elements for a fire: the coil acting as an ignition
source, the hose material acting as a fuel, and the oxygen
to promote burning.

Boeing had previously identified safety issues involving
conductive hoses and had issued a service bulletin
instructing operators of aircraft with these hoses in the
cockpit to replace them with nonconductive ones.  The FAA
approved the bulletin but did not issue an airworthiness
directive to make compliance with the bulletin mandatory.

The Safety Board also found that other ABX 767 aircraft's
supplemental oxygen system did not include positive
separation between electrical wiring and oxygen system
tubing. Electrical wiring that is near or in contact with
oxygen system tubing creates the potential for electrical
short circuits to reach the oxygen system hoses. The
involvement of oxygen in a fire can significantly expedite
its growth and severity.

Prior to the accident, ABX maintenance personnel performed
numerous instances of oxygen system servicing on the
accident aircraft, indicating a chronic problem on the
airplane. However, ABX did not develop a specific action
plan to resolve the identified discrepancies. The lack of
further action was not stipulated by ABX's continuing
analysis and surveillance program (CASP).  The Safety Board
determined that ABX's CASP did not properly address and
correct the oxygen leaks. However, these previous oxygen
leaks did not directly cause the fire.

"The hose design issue, which was one factor that gave rise
to this accident, should have provided the FAA with plenty
of warning that, if left unaddressed, could result in a
serious accident, as we have seen here," said NTSB Acting
Chairman Mark V. Rosenker.  "Had the fire started when the
plane was in the air, the result would very likely have been
catastrophic."

As a result of the investigation, the Safety Board voted to
recommend that the FAA: require operators to replace
electrically conductive hoses with electrically
nonconductive hoses and prohibit further use of conductive
hoses unless the conductivity is an approved design element;
formalize the airworthiness directive (AD) process so it
addresses all possible uses of an appliance affected by an
AD; require positive separation between electrical wiring
and oxygen system tubing; ensure that oxygen system tubing
in proximity to electrical wiring is made of, sleeved with,
or coated with nonconductive material or is isolated from
potential electrical sources; develop and implement
electrical grounding requirements for oxygen system
components for all transport-category aircraft;  develop
inspection criteria or service life limits for flexible
oxygen hoses to ensure that they meet current certification
and design standards and require that airplane operators
replace hoses that do not meet these criteria or life
limits; and require operators of transport-category cargo
airplanes to install smoke detectors in the supernumerary or
similar airplane compartments.

During its investigation, the Safety Board determined that
reading lights located in passenger service units (PSU)
could become a potential source of ignition to nearby
combustible materials.  Because of this, the Board
recommended that the FAA require transport-category airplane
operators to ensure that all reading lights in PSUs be
installed with rubber boots or use other means to provide a
greater level of electrical protection.

The Safety Board also voted to recommend that ABX Air modify
its CASP so that all chronic discrepancies are effectively
resolved.  And the Board reiterated a previous
recommendation to the FAA about training on an emergency
response firefighting device.

A synopsis of the accident investigation report, including
the findings, probable cause, and safety recommendations,
can be found on the Publications page of the Board's
website, http://www.ntsb.gov/Publictn/2009/AAR0904.htm. The
complete report will be available on the website in several
weeks.

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NTSB Media Contact: Peter Knudson
(202) 314-6100
peter.knudson@xxxxxxxx

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