|Re: Metric vs. US model of HP 50g|
Message #26 Posted by Geoff Quickfall on 30 Jan 2010, 3:46 p.m.,
in response to message #17 by Glenn Shields
I actually flew the "Gimli Glider" before it was retired from service last year.
Fuelling in an imperial measure with metric units in an aircraft
with correct sensing fuel gauges as well as fuel flow guages.
1. First, while sitting in the cockpit, the fuel guy hands you a
receipt in gallons or litres of Jet A fuel loaded.
2. This gets converted by multiplying with a specific gravity (
S.G.)to kilograms of fuel. The guages are in kilograms in
Canadian Aircraft. The S.G. is temperature specific and varies
each day. The fuel remaining in a tank is usually cold from
altitude to landing and the S.G. will not be the same as the
loaded fuel. Fortunately the fuel remaining in tank after landing
is usually a percentage of the fuel loaded for the next flight and
therefore has a small error to the total calculations.
3. Add the fuel on board (FOB) at landing to the converted to
kilograms fuel boarded (TENDERED FUEL) and you have the total fuel.
4. Ways to check fuel consumption in the air. Five hour (Toronto
to Vancouver B767) flight times on average 5000 kg/hour and you
will burn 35,000kgs. The average varies due to weight of
aircraft, winds and etc. This plus operational taxi fuel, holding
fuel, alternate fuel, approach fuel, 5% slop fuel and you may have
45000 kgs on board. So if all goes correctly and you arrive on
sched as planned then you should have approximately 10000 kgs
remaining. The guages will do an analog or digital calculation
based on sensors in the tank, temperature and display kilograms
remaining (Fuel in tank). The computers using fuel flow will
calculate the fuel in tank by taking the original FOB and
subtracting the fuel flow versus time (calculated fuel in tank).
This is all displayed info in the aircraft.
NOW for the Gimli glider:
1. New aircraft to the fleet and relatively new to Canada
operations and the MOT (our FAA). Also the first Aircraft in
Canada at AC with metric guages.
2. Fuel guages inoperative at the gate so no display of fuel.
Fuel guages at the wing fuelling points also unservicable. Fuel
flow system inoperative so no calculated remaining fuel
indication. Not a problem usually, as one has drip sticks that
will measure the depth of the fuel in the three tanks and can be
accessed after fueling. The sticks WERE in inches at the time of
purchase. The Air Canada charts had been converted to metric so
the inches on the sticks had to be converted to cm on the chart by
maintenance in conjunction with the fueller who was delivering
fuel by the litre which had to be converted to kilograms with an
S.G. The mistake was made at the conversion of depth of fuel in
inches to cms by maintenance.
3. No indications in the air as to actual fuel via guages on
tanks or fuel flow on board and since the error was made at the
drip stick measurement, the incorrect total fuel on board was
delivered to the pilots. They followed the book by using the
maintenance procedure to measure fuel in tanks with the drip
sticks. As a result, they did their rough math of X amount of
fuel divided by the average for the flight and came up with
sufficient. This would normally be compared to the onboard system
which will display insufficient fuel but did not due to a KNOWN
technical problem which pecipitated the drip stick measurment by
4. Rectification. Well every where we go we get fuel loaded in
litres except for the US. All guages on the aircraft are metric.
Conversion is done from gallons to kilograms based on the S.G.
No aircraft can be dispatched with a multiple fuel indication
failure now. At least one of the systems must be in place as a
check against the fueler, aircraft, pilots and maintenance.
The aircraft should be controllable in any loss of all engine circumstance, the skill entered when the F/O new of a decomissioned airforce runway which was obtainable in the glide, otherwise this aircraft would have landed in a field. Instead it was repaired and flew until 2008. By the way, an B767 should glide about 90 miles if at 30,000 feet.
Kind of an extremely reduced synopsis of the situation. But it sure does indicate how complicated a simple system can become:
Inches to cms, cms via a chart to kilograms, fuel boarded in gallons converted via SG to kilograms. Broken fuel guages system including the fuel flow system and both sets of guages; cockpit and wing fuel point.....
p.s. I am doing this from memory as I was at Canadian Airlines at the time of the incident. The problem is the fuel was boarded ultimately in pounds and labeled kilograms. So 27000 pounds incorrectly labeled 27000 kilograms would equate 12,244 kilograms. Well short of the required fuel!
Edited: 30 Jan 2010, 3:58 p.m.