U.S. air safety regulators expect to
release at least four more
airworthiness directives involving MD-11
trijet wiring sometime this
week or early next week, according to
Aero Safety & Maintenance.
The four will cover the center accessory
compartment, a cockpit
overhead switch panel, the aft main
avionics rack and the galley load
control unit, an FAA spokesman confirms
to AS&M. They're only
the latest in a series of inspection
orders on MD-11 wiring; most
recently, the FAA ordered inspection
and possible replacement of
electrical wiring above the forward
passenger doors and cockpit and
cabin wiring and insulation.
The spokesman didn't say how the four
ADs relate to efforts now
underway by the Los Angeles Aircraft
Certification Office to come up
with an MD-11 "corrective action
plan." Nor could he say whether a
problem uncovered last week during an
C-check on a World
Airways MD-11 would result in another
AD in the upcoming batch of
orders.
Technicians at Santa Barbara Aerospace
working on that aircraft
found burn residue on an insulating
blanket under the floorboards in
the aft cargo compartment. An engineer
from the Los Angeles office
inspected the aircraft a week ago, and
believes the burn was caused
by wire harnesses "riding hard"
on the blanket. Further inspection
showed one cut wire and more chafing,
and officials think the standoff
height may be too short for the cargo
loader harness to ride on the
aircraft frame at that station.
It's not a safety of flight issue —
the wiring involved is for the aft
cargo controller/loader, which is only
powered when the plane is on
the ground, the cargo door open and
the joystick that controls the
loader is in use. Still, FAA and Boeing
Long Beach engineers are
working quickly to come up with a service
bulletin correcting the
cargo loader wiring harness installation,
and the agency is also looking
over the design drawings in case there
may be a design flaw.
Officials say the corrective action
in this case will be made part of the
overall MD-11 corrective action plan,
but haven't said in what way
this will be done.
Although the last MD-11 wiring AD —
for the area above the
forward passenger door — wasn't
directly related to the September
crash of a Swissair MD-11 trijet, the
AD's text said it was the result
of "test results obtained in support
of an accident investigation."
Investigators working on the Swissair
111 probe singled out the area
aft of the cockpit door for a closer
look as a potential source of the
flight's fatal fire. In addition, the
inflight gaming system got a lot of
attention from investigators involved
in the case. Sources familiar with
the probe have said that the specific
path of damage in the aircraft's
wiring — what showed burn damage
and what did not — suggests
the system wiring running between the
cockpit and cabin of the
Swissair MD-11 could have been a starting
point for the deadly fire. -
Jim Mathews and Sean Broderick/Aero
Safety & Maintenance
04/06/99
