The subsequent investigation revealed corporate failures and a chain of minor human errors that combined to defeat built-in safeguards. In addition, fuel loading was miscalculated through misunderstanding of the recently adopted metric system, which replaced the imperial system.
On 22 July 1983, the day before the incident, Air Canada's Boeing 767 (registration C-GAUN, c/n 22520/47) flew from Toronto to Edmonton where it underwent routine checks. The next day it was flown to Montreal. Following a crew change, it departed Montreal as Flight 143 for the return trip to Edmonton via Ottawa, with Captain Robert (Bob) Pearson and First Officer Maurice Quintal at the controls.
At 26,000 feet (7,900 m), over Red Lake, Ontario, the aircraft's cockpit warning system sounded, indicating a fuel pressure problem on the aircraft's left side. Assuming that a fuel pump had failed,[3] the pilots turned it off,[3] as gravity would still feed fuel to the aircraft's two engines. The aircraft's computer indicated that there was still sufficient fuel for the flight, but, as the pilots subsequently realized, the calculation was based on incorrect settings. A few moments later, a second fuel pressure alarm sounded, prompting the pilots to divert to Winnipeg. Within seconds, the left engine failed and they began preparing for a single-engine landing.
As they communicated their intentions to controllers in Winnipeg and tried to restart the left engine, the cockpit warning system sounded again, this time with a long "bong" that no one present could recall having heard before.[3] This was the "all engines out" sound, an event that had never been simulated during training.[4] Seconds later, most of the instrument panels in the cockpit went blank as the right-side engine also stopped and the 767 lost all power.
The 767 was one of the first airliners to include an Electronic Flight Instrument System (EFIS), a system that required the electricity generated by the aircraft's jet engines in order to operate. With both engines stopped, the system went dead, leaving only a few basic battery-powered emergency flight instruments. While these provided basic but sufficient information with which to land the aircraft, a vertical speed indicator – that would indicate the rate at which the aircraft was sinking and therefore how far it could glide unpowered – was not among them.
In airliners the size of the 767, the engines also supply power for the hydraulic systems without which the aircraft cannot be controlled. Such aircraft are therefore required to accommodate this kind of power failure. As with the 767, this is usually achieved through the automated deployment of a ram air turbine, a generator driven by a small propeller, which in turn is driven by the forward motion of the aircraft. As the Gimli pilots were to experience on their landing approach, a decrease in this forward motion means a decrease in the power available to control the aircraft.
In line with their planned diversion to Winnipeg, the pilots were already descending through 28,000 feet (8,500 m) when the second engine shut down. They immediately searched their emergency checklist for the section on flying the aircraft with both engines out, only to find that no such section existed.[5] Captain Pearson, however, was an experienced glider pilot, which gave him familiarity with some flying techniques almost never used by commercial pilots. In order to have the maximum range and therefore the largest choice of possible landing site, he needed to fly the 767 at the "best glide ratio speed". Making his best guess as to this speed for the 767, he flew the aircraft at 220 knots (410 km/h; 250 mph). First Officer Maurice Quintal began making calculations to see if they could reach Winnipeg. He used the altitude from one of the mechanical backup instruments, while the distance traveled was supplied by the air traffic controllers in Winnipeg, measuring the distance the aircraft's echo moved on their radar screens. The aircraft had lost 5,000 feet (1,500 m) in 10 nautical miles (19 km; 12 mi), giving a glide ratio of approximately 12:1. The controllers and Quintal both calculated that Flight 143 would not make it to Winnipeg.
At this point, Quintal proposed landing at the former RCAF Station Gimli, a closed air force base where he had once served as a Canadian Air Force pilot. Unknown to him, however, one of the two parallel, equal length runways was now being used as a dragstrip. The other runway was used regularly and maintained to a serviceable condition year round. As a result of the conversion to a dragstrip, the runway now had two racing lanes separated by a guard rail running down the middle. Furthermore, a "Family Day" was underway that day and the area around the decommissioned runway was full of cars and campers. The decommissioned runway itself was being used to stage a race.
Without power, the pilots had to try lowering the aircraft's main landing gear via a gravity drop, but, due to the airflow, the nose wheel failed to lock into position. The decreasing forward motion of the aircraft also reduced the effectiveness of the Ram Air Turbine (RAT), making the aircraft increasingly difficult to control because of the reduced power being generated.
As the runway drew nearer, it became apparent that the aircraft was too high and fast, raising the danger of running off the runway before the aircraft could be stopped. The lack of hydraulic pressure prevented flap/slat extension. These devices are used under normal landing conditions to reduce the speed of the aircraft for a safe landing. The pilots briefly considered executing a 360 degree turn to reduce speed and altitude, but came to the conclusion they did not have enough altitude for the maneuver. Pearson decided to execute a forward slip to increase drag and lose altitude. This maneuver is commonly used with gliders and light aircraft to descend more quickly. At the time Pearson executed the slip, the aircraft was flying over a golf course.
As soon as the wheels touched the runway, Pearson "stood on the brakes", blowing out two of the aircraft's tires. The unlocked nose wheel collapsed and was forced back into its well, causing the aircraft's nose to scrape along the ground. The plane also slammed into the guard rail now separating the strip, which helped slow it down.
None of the 61 passengers was seriously hurt. A minor fire in the nose area was soon put out by racers and course workers armed with fire extinguishers. As the aircraft's nose had collapsed onto the ground, its tail was elevated and there were some minor injuries when passengers exited the aircraft via the rear slides. These were treated by a doctor who had been about to take off in an aircraft on Gimli's remaining runway.An Air Canada investigation concluded that the pilots and mechanics were at fault. It was also subsequently investigated by the predecessor of the modern Transportation Safety Board of Canada; while concluding that Air Canada management was responsible for "corporate and equipment deficiencies", the report praised the flight and cabin crews for their "professionalism and skill". It noted that Air Canada "... neglected to assign clearly and specifically the responsibility for calculating the fuel load in an abnormal situation", finding that the airline had failed to reallocate the task of checking fuel load that had been the responsibility of the flight engineer on older (three-crew) aircraft.
Information about the amount of fuel in the tanks of a Boeing 767 is computed by the Fuel Quantity Indicator System (FQIS) and displayed on gauges in the cockpit. The FQIS on the incident aircraft was a dual processor channel, each calculating the fuel independently and cross-checking with the other. In the event of one failing the other could still operate alone, but under these circumstances the indicated quantity was required to be cross-checked against a floatstick measurement before departure. In the event of both channels failing there would be no fuel display in the cockpit, and the aircraft would be considered unserviceable and not authorized to fly.
After inconsistencies were found with the FQIS in other 767s, Boeing issued a service bulletin for the routine checking of this system. An engineer in Edmonton duly did so when the aircraft arrived from Toronto following a trouble-free flight the day before the incident. It was while conducting this check that the FQIS failed completely and the cockpit fuel gauges went blank. The engineer had previously encountered the same problem earlier in the month when the same aircraft had arrived, again from Toronto, with an FQIS fault. He found then that disabling the second channel by pulling the circuit breaker in the cockpit restored the fuel gauges to working order albeit with only the single FQIS channel operative. In the absence of any spares he simply repeated this temporary fix by pulling and tagging the circuit breaker.
On the day of the incident the aircraft flew from Edmonton to Montreal. Before departure the engineer informed the pilot of the problem and confirmed that the tanks would have to be checked with the floatstick. In a misunderstanding however the pilot believed that the aircraft had been flown with the fault from Toronto the previous afternoon. That flight proceeded uneventfully with fuel gauges operating correctly on the single channel.
On arrival at Montreal there was to be a crew change for the return flight back to Edmonton. The outgoing pilot informed Captain Pearson and First Officer Quintal of the problem with the FQIS and passed on his mistaken belief that the aircraft had flown the previous day with this problem. In a further misunderstanding Captain Pearson believed that he was also being told that the FQIS had been completely unserviceable since then.
While the aircraft was being prepared for its return to Edmonton, a maintenance worker decided to investigate the problem with the faulty FQIS. In order to test the system he re-enabled the second channel, at which point the fuel gauges in the cockpit went blank. He was then called away to perform a floatstick measurement of fuel remaining in the tanks. Distracted, he failed to disable the second channel, leaving the circuit breaker tagged (which masked the fact that it was no longer pulled). The FQIS was now completely unserviceable and the fuel gauges were blank.
A record of all actions and findings was made in the maintenance log, including the entry; "SERVICE CHK – FOUND FUEL QTY IND BLANK – FUEL QTY #2 C/B PULLED & TAGGED...". This reports that the fuel gauges were blank and that the second FQIS channel was disabled, but does not make clear that the latter fixed the former.
On entering the cockpit Captain Pearson saw what he was expecting to see; blank fuel gauges and a tagged circuit breaker. He consulted the aircraft's Minimum Equipment List (MEL), which told him that the aircraft could not be flown in this condition. However, the 767 was still a very new aircraft, having flown its maiden flight in September 1981. C-GAUN was the 47th Boeing 767 off the production line, delivered to Air Canada less than 4 months previously.[9] In that time there had already been 55 changes to the MEL, and some pages were still blank pending development of procedures. As a result of this unreliability it had become practice for flights to be authorised by maintenance personnel. To add to his own misconceptions about the condition the aircraft had been flying in since the previous day, reinforced by what he saw in the cockpit, he now had a signed off maintenance log that it had become custom to prefer above the Minimum Equipment List.
At the time of the incident, Canada was converting to the metric system. As part of this process, the new 767s being acquired by Air Canada were the first to be calibrated for the new system, using litres and kilograms instead of gallons and pounds. All other aircraft were still operating with Imperial units (gallons and pounds). For the trip to Edmonton, the pilot calculated a fuel requirement of 22,300 kilograms (49,000 lb). A dripstick check indicated that there were 7,682 litres (1,690 imp gal; 2,029 US gal) already in the tanks. In order to calculate how much more fuel had to be added, the crew needed to convert the quantity in the tanks to a weight, subtract that figure from 22,300 and convert the result back into a volume. (In previous times, this task would have been completed by a flight engineer, but the 767 was the first of a new generation of airliners that made this position redundant.)
A litre of jet fuel weighs 0.803 kg, so the correct calculation was:
7682 litres × 0.803 = 6169 kg
22300 kg − 6169 kg = 16131 kg
16131 kg ÷ 0.803 = 20088 litres of fuel to be transferred
Between the ground crew and flight crew, however, they arrived at an incorrect conversion factor of 1.77, the weight of a litre of fuel in pounds. This was the conversion factor provided on the refueller's paperwork and which had always been used for the rest of the airline's imperial-calibrated fleet. Their calculation produced:
7682 litres × 1.77 = 13597 kg
22300 kg − 13597 kg = 8703 kg
8703 kg ÷ 1.77 = 4916 litres of fuel to be transferred
Instead of 22,300 kg of fuel, they had 22,300 pounds' on board — only a little over 10,000 kg, or less than half the amount required to reach their destination. Knowing the problems with the FQIS, Captain Pearson double-checked their calculations but was given the same incorrect conversion factor. All he did was check their arithmetic, inevitably coming up with the same erroneous figures.
The Flight Management Computer (FMC) measures fuel consumption, allowing the crew to keep track of fuel burned as the flight progresses. It is normally updated automatically by the FQIS, but in the absence of this facility it can be updated manually. Believing he had 22,300 kg of fuel on board, this is the figure the captain entered.
Because the FMC would reset during the stopover in Ottawa, the captain had the fuel tanks measured again with the dripstick while there. In converting the quantity to kilograms, the same incorrect conversion factor was used, leading him to believe he now had 20,400 kg of fuel; in reality, he had less than half the required amount.It has been reported that, following Air Canada's internal investigation, Captain Pearson was demoted for six months, and First Officer Quintal was suspended for two weeks. Three maintenance workers were also suspended. Nevertheless, in 1985 the pilots were awarded the first ever Fédération Aéronautique Internationale Diploma for Outstanding Airmanship. Quintal was promoted to Captain in 1989, while Pearson retired in 1993.
C-GAUN, fin 604, was patched at Gimli and flown out two days later. It remained in service with Air Canada until almost a quarter century later; it flew its last revenue flight (AC951 from Port-au-Prince, Haiti to Montreal, Canada) on 1 January 2008. Air Canada still uses Flight 143 for its Montreal-Ottawa-Edmonton route.
On 24 January 2008, the Gimli Glider took its final voyage, AC7067, from Montreal Trudeau to Mojave Airport before its retirement in the desert where it was used for parts. An Air Canada newsletter, "The Daily" states:
The Gimli Glider retires to the desert. On Thursday, 24 January, fin 604, the Boeing 767-200 better known as the Gimli Glider, will undertake its final voyage from Montreal to Mojave Airport (MHV) before it is retired to the desert. Employees and retirees (bring valid employee ID) are invited to come and say goodbye to the aircraft, which has now become part of Canadian aviation history. Fin 604 is set to depart as flight AC7067, at 9 a.m. from the Montreal Line Maintenance hangar - Air Canada Base, 750 Côte Vertu West; Building 7, Bay 8/13 (West end), Gate entrance 5. Captain Robert Pearson and First Officer Maurice Quintal, the flight crew who landed the aircraft to safety in Gimli on 23 July 1983 are expected to be on hand for the aircraft's departure. The hangar will be open to well-wishers from 8:00 a.m.
Flight AC7067 was captained by Jean-Marc Bélanger, a former head of the Air Canada Pilots Association, while Captain Robert Pearson and Maurice Quintal were on board to oversee the flight from Montreal to California's Mojave Airport, its final resting place. Also on board were three of the six original flight attendants who were on Flight 143.[15][16] Flight tracking services FlightAware and FlightView indicated on 24 January 2008 that 604's initial flight was from Montreal (CYUL) to Tucson International airport (KTUS), having a planned cruise altitude of FL400. According to FlightAware, 604 landed at 12:53 P.M. (MST) at Tucson International airport (KTUS). The Gimli Glider was then scheduled (but delayed) to depart Tucson and make the final flight to the Mojave Airport (KMHV) for retirement.
On the 25th anniversary of the incident in 2008, pilots Pearson and Quintal were celebrated in a parade in Gimli, as a mural was dedicated to commemorate the landing.
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