An insistent warning buzzer sounded and an amber light flashed.
ÒSomethingÕs
wrong with the fuel pump," announced the first officer after he had
glanced at the indicators in front of him.
ÒLeft
forward fuel pump,Ó added the captain. ÒI hope itÕs just the fuel pump failing,
IÕll tell you that.Ó
On the
afternoon of July 23, 1983, the fully-fuelled Flight 143 had taken off from
Montreal into blue sky and clear air heading towards Edmonton that included a
short non-refuelling stop at Ottawa. The captain and first officer in the
cockpit were among only a handful of pilots trained to fly the twin-engine 767,
then the most advanced jet-liner in the world. This Boeing was such a new
addition to the Air Canada fleet of aircraft that the written maintenance
standards were still being revised.
When the
ground crew was preparing the plane for departure from Montreal, they found
that the fuel gauge did not work and there was no replacement computer
available, but a maintenance worker had incorrectly assured the captain that
the plane was still certified to fly without a functioning fuel gauge as long
as the crew manually checked the quantity of fuel in the tanks. Each fuel tank
contained a drip stick and the manual "drip" procedure was a
well-established operation where a mechanic would loosen the stick under the
wing to allow it to drop within the tank until a float at its tip bobbed on the
surface of the fuel. A technician could then read the depth of the fuel from
markings on the drip stick and consult a handbook that gave the corresponding
volume of fuel in the tank. The 767 had three fuel tanks, one in each wing and
one in the planeÕs belly and each tank was served by two pumps. This ensured a
steady stream of fuel was delivered to both engines.
ÒDensity
is mass divided by volume or the volume times the mass of one litre of fuel
will give the weight,Ó the first officer had offered before turning to the
mechanic in charge of refuelling and asking for the factor for converting
litres into kilograms.
Ò1.77,Ó
the refueller had answered.
Using this
value, the calculation was made and the necessary extra fuel for the journey to
Edmonton added. Drip checks were completed until the captain was satisfied that
the plane was fully fuelled. No one had confirmed the units that should be
applied to this number. For many years Air Canada had computed the amount of
fuel needed in pounds, but the new 767Õs fuel consumption was expressed in
kilograms. The units of measure were in accord with the Canadian governmentÕs
plan to introduce metric units nationwide and fuel loading was usually the responsibility
of the flight engineer, but in this technologically advanced aircraft, the
manning level now comprised only the two pilots and no longer a flight engineer
so it was unclear who actually had responsibility for determining fuel loading.
The important
factor at take-off is always the total weight of the aircraft.
The
airliner cruised at four hundred and sixty nine knots above cottony clouds as it neared the route
checkpoint of Red Lake, Ontario. The easy-to-read displays on computer screens in
the sophisticated instrument panel were designed to reduce pilot fatigue on
long flights and on this four-hour trip to Edmonton, the captain expected to
relax a little as he carried his sixty one passengers to western Canada.
A warning
buzzer indicated three possible problems and each could be happening separately
or some combination of all three. The pump itself had failed, a fuel line was
clogged or the left tank was running dry. In any case, according to the
reference handbook normal flight was still possible with one defective fuel
pump.
More
alarms sounded after a few seconds of silence had passed. The second of the two
pumps in the left wing tank was also failing and it was too much of a
coincidence for both pumps to fail at the same time. The tank was running out
of fuel.
ÒWeÕve got
to go to Winnipeg,Ó asserted the captain as he set a course for this nearest
large airport. The first officer radioed air traffic control and they received
immediate clearance to descend to six thousand feet. More beeps signalled the worst possible news:
the four remaining fuel pumps from the other two tanks were now also failing.
The
left engine had stopped running.
ÒWeÕve
lost our number one engine and weÕll require all the fire trucks out,Ó the
first officer radioed, anticipating a crash landing.
The
pilots set the flaps for a landing with only one engine.
As
they passed twenty six thousand
feet, the remaining engine stopped and the cockpit became very quiet. Without
power the computer screens flickered off and the high-tech displays were dark
and useless. They were still one hundred miles from Winnipeg.
The
unthinkable had happened. The worldÕs most advanced aircraft had run out of
fuel and at twenty six thousand
feet had become just a massive glider.
The
jet-liner silently overflew Red Lake on towards Winnipeg and the pilots and air
traffic controllers made some hasty calculations. They reached the grim
conclusion that without engines the aircraft's rapid descent would bring the
aircraft in at least ten miles short
of the airport at Winnipeg. The preflight fuel calculation was not considered.
They were directed to Gimli, a now abandoned airport once used by the Royal Canadian Air Force that was unsuitable for landing a 767. No other runway was within gliding range and there were no fire trucks. Swooping quietly over Lake Winnipeg toward Gimli, the pilots realised that the plane was coming in too high and they would land too far down the runway and skid off the end. In a desperate move to lose altitude, the 'side slip' manoeuvre that is used in small planes was tried even though this was unheard of in a jet-liner. Turning the wheel for a left turn and pushing the rudder for a right turn, the plane fought with itself and descended faster. The plane tipped sharply onto its side and the passengers gasped in horror as through the windows they could see the ground growing closer. At the last moment the plane was righted, but now at the correct height for an attempted landing.
Without
power there was only the one chance to get it right.
The
strip of concrete was no longer a runway and had been converted into a car
racing track complete with fencing to protect the spectators. Fate would have
it that a race meeting would be under way that particular day with many, many
spectators. Shocked people on the ground dived for cover to get out of the path
of the rapidly descending plane.
After
twenty nine minutes without power
the 767 touched down just eight hundred feet from the start of the runway. Not very far ahead was a steel
barricade. Two tyres blew out and the aircraft threatened to skid off the
runway. Suddenly, the front landing gear collapsed and the nose of the plane
scraped along the runway throwing out dangerous sparks. Without engine power
reverse thrust could not be used, yet miraculously the plane slowed and finally
stopped just in front of the barrier. Fearing fire, the flight attendants
rushed the passengers down the emergency ramps. There were many scrapes and
bruises, but only a few real injuries.
The
passengers and crew of Flight 143 had made it.
The
Boeing 767 was thoroughly repaired and Air Canada put it back into service. The
completely revised maintenance manual now had the explicit fuel density value
specified as 0.803 kilograms per litre to ensure that the value of Ò1.77Ó could
never again be interpreted as pounds per litre. No calculation error had been
made in the fuel weight figures, but the wrong units had nearly ended with a
terrible air disaster when less than half the true weight of fuel had been
loaded. Training flight simulators were designed to practise short landings
without engine power. The usual outcome was a crash and this constantly
illustrated the truly skilful piloting that had brought Flight 143 safely to
the ground. Flight crews from that day onwards called the aircraft the Gimli
Glider.
© Louis Brothnias (2011)