Re: old DC10 crash in Portland

From:         ehahn@fairlite.mitre.org (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         07 Mar 94 15:12:48 PST
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   However, she swears that right
   after the crash, the pilot was telling anyone who would listen that
   the instruments indicated, as I recall, 200-300 lbs of fuel left in
   each wing when the engines went down.

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----
200-300 pounds of fuel is well within the realm of uncertainty in fuel
quantity measurement, especially with the fuel quantity indication
system (FQIS) of the era.

FQIS is a perennial headache to maintain, as there is no good way to
measure it.  The standard method is to look at the capacitance of the
fuel, which is loosely proportional to the amount of fuel in the
wings.

The capacitance is measured by looking for the resonant
frequency in a fuel quantity probe, ala first year electronics.
Naturally, the probe leads, which are soaked in fuel, will fall out of
calibration fairly quickly.

Most of the time, this doesn't matter, as the fuelers use dipsticks to
verify the amount of fuel in the wings.  However (this may be
hindsight), they just aren't that accurate when the tanks are THAT
empty.

Even with new digital FQIS systems, FQIS is still a leading cause of
maintenance delays ("call maintenance, the FQ is reading too low"), at
least among the airlines I've worked with.

Just my $0.02,
ed

////////   Ed Hahn | ehahn@mitre.org | (703) 883-5988   \\\\\\\\
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.