Re: How do fuel guages work?

From: (Eric Olesen)
Organization: Texas Metronet, Inc  (login info (214/705-2901 - 817/571-0400))
Date:         27 Aug 95 14:37:14 
References:   1 2 3
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Jay Vassos-Libove ( wrote:
: This incident became known as the Gimli Glider.  The 767 was misfueled
: because all of its fuel gauges were either malfunctioning or were
: incorrectly checked. As a result, the aircraft (according to airline
: rules) should not have been dispatched at all.

>From my recollection, the gauges were placarded as inoperative by
maintenance against the MEL list (min equip list). Dispatch was
permitted and legal using the specs that were in place at the time.

: Instead, as it was a new aircraft, and there was pressure to get the
: aircraft out on time, the aircraft was fueled with checks done by
: converting a dipstick measurement in the tanks from a linear (probably
: metric) : measurement to a volumetric (english, since it was a 767)
: measurement... and somebody got a conversion factor exactly
: backwards, resulting in *4 instead of /4, so they put 1/4 the
: necessary fuel on board.

Both the fueler and the first officer made the same conversion error...
Once the tanks were dipsticked for quantity, dispatch was legal because
the fuel quantity was entered into the Flt Management Computer.. This
was supposed to track consumption based on the fuel flow into the
engines. The problem was that the incorrect fuel quantity was entered
into the FMC, so it was correct about how much fuel was consumed, but
also 'thought' that there was about 60% more fuel onboard than there
really was. At the time they lost engines, the FMC was still showing that
there was fuel onboard...

So... had the right amount been entered into the FMC, there should not
have been a problem with dispatching the aircraft with the fuel quantity
gauges placarded as inoperative. I believe that this is still on the MEL
and procedurally OK with some carriers, although I also seem to remember
that AC changed the way that fuel was measured in metrics vs. English units.