(This is a letter from Boeing to the NTSB. It is available
from the NTSB website at
www.ntsb.gov/events/EA990/docket/Ex_8A_app6.pdf.
But this information was well known in the aviation community. I
was told about it by a flight instructor in L.A., and then verified it
through the NTSB at this site.)
Ronald J. Hinderberger
Director
Airplane Safety
Commercial AIrplanes Group
me Brx!ll-ly CL; ., ,:i: ,y
P.O. Box 3707 MC 67.XK
Seattle. WA 98123-2207
11 February 2000
B-H200-16888-ASI
Mr. Jim Hookey, AS-40
National Transportation Safety Board, AS-40
490 Lí Enfant Plaza East, SW
Washington, DC 20594
Subject: Engine Fuel Flow FDR Data - Egyptair 767-300ER SU-GAP,
Accident Off Nantucket, Massachusetts - 31 October, 1999
Reference: Our letter B-H200-16868-ASI, 18 January 2000
Dear Mr. Hookey:
Per your request, please find the contents of the reference letter
reiterated
below.
Backaround
During the Egypt Air 990 descent, both engineís Fuel Control
Switches were
moved to CUTOFF, and as expected the FDR data showed
that there were
immediate positive indications that fuel was cut to the engine (e.g.
rotor speed
and EGT decrease). However, the FDR data indicated that Fuel Flow for
both
engines remained steady at idle levels (approximately 1300 Ibs./hr)
for four
seconds after engine shutdown. From the other indications it can be
determined that this Fuel Flow indication was not accurate. A review
of the
Fuel Flow Indication System was undertaken to explain why this occurred.
Results from the Svstem Review
The factors contributing to the Fuel Flow FDR characteristics are as
follows:
Il. The Fuel Valve closure rate is on the order of 250 msec once the
command
from the Fuel Control Switch is moved to CUTOFF.
2. The EICAS incorporates the following filter: ëWhen no Fuel Flow
activity
exists or its input sample is less than 300 Ibs./hr, and persists for
1.5 seconds,
then set the resulting filtered value to zero. While this time delay
is running,
but not expired, then the previous sampled value prior to the activation
of the
time delay, shall continue to be input to the filter.í This EICAS filtered
Fuel
Flow is sent to the Flight Data Recorder (FDR) to be recorded. This
1.5-
second time delay will occur every time the engine is shutdown.