An insistent warning buzzer sounded and an amber light flashed.
“Something’s wrong with the fuel pump," announced the first officer after he had glanced at the indicators in front of him.
“Left forward fuel pump,” added the captain. “I hope it’s just the fuel pump failing, I’ll tell you that.”
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 plane’s belly and each tank was served by two pumps. This ensured a steady stream of fuel was delivered to both engines.
“Density is mass divided by volume or the volume times the mass of one litre of fuel will give the weight,” the first officer had offered before turning to the mechanic in charge of refuelling and asking for the factor for converting litres into kilograms.
“1.77,” 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 767’s fuel consumption was expressed in kilograms. The units of measure were in accord with the Canadian government’s 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.
“We’ve got to go to Winnipeg,” 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.
“We’ve lost our number one engine and we’ll require all the fire trucks out,” 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 world’s 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 “1.77” 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)