Air Canada Flight 143 was a scheduled domestic passenger flight between Montreal and Edmonton. On July 23, 1983, the Boeing 767 ran out of fuel midway through the flight.
The fuel gauge was not operating, and the plane's tanks had been underfilled because of an incorrect calculation.
The flight crew successfully glided the aircraft from an altitude of 41,000 feet (12,500 m) to an emergency landing at a former Royal Canadian Air Force base in Gimli, Manitoba, which had been converted to a racetrack, Gimli Motorsports Park. The landing caused no serious injuries to passengers or persons on the ground, and only minor damage to the aircraft. The aircraft was repaired, and remained in service until its retirement in 2008. This unusual aviation accident earned the aircraft the nickname "Gimli Glider".
The accident was caused by a series of issues, including a failed fuel-quantity indicator sensor (FQIS) and confusion between pounds and kilograms. The fuel sensors in 767s had high failure rates, and the only replacement sensor available when the failure was detected was also nonfunctional. This problem was logged when it was discovered, but later, the maintenance crew misunderstood the problem and turned off the backup FQIS. This required the volume of fuel to be manually measured using a dripstick.
The navigational computer required a number to be entered specifying the amount of fuel on board, in kilograms; however, an incorrect conversion from volume to mass was applied, which led the pilots and ground crew to agree that there was enough fuel for the remaining trip when it was actually 45% of the required amount. The aircraft ran out of fuel halfway to Edmonton, where maintenance staff were waiting to install a working FQIS that they had borrowed from another airline.
The Board of Inquiry found fault with Air Canada procedures, training, and manuals. It recommended the adoption of fuelling procedures and other safety measures that U.S. and European airlines were already using. The board also recommended the immediate conversion of all Air Canada aircraft from imperial units to SI units, since a fleet using a mix of units was more dangerous than an all-imperial or an all-metric fleet.
The aircraft involved, manufactured in 1983,MSN 22520 and line number 47, was a Boeing 767-233 registered as C-GAUN. It was powered by two Pratt & Whitney JT9D-7R4D engines.
On July 22, 1983, Air Canada Boeing 767 C-GAUN underwent routine checks in Edmonton. The technician found a defective FQIS, so he disabled the defective channel and made an entry in the logbook. The next morning, Captain John Weir and co-pilot Captain Donald Johnson were told about the problem. Since the FQIS was now operating on a single channel, a dripstick reading was taken to obtain a second fuel quantity measurement. Weir converted the dripstick reading from centimetres to litres to kilograms, finding that it agreed with the FQIS. The plane flew to Toronto and then Montreal without incident.
At Montreal, Captain Bob Pearson and First Officer Maurice Quintal took over the airplane for Flight 143 to Ottawa and Edmonton. During the handover, Weir told Pearson that a problem existed with the FQIS, and Pearson decided to take on enough fuel to fly to Edmonton without refuelling in Ottawa. Meanwhile, an avionics technician had entered the cockpit and read the logbook. While waiting for the fuel truck, he enabled the defective channel and performed an FQIS self-test. Distracted by the arrival of the fuel truck, he left the channel enabled after the FQIS failed the test. Pearson entered the cockpit to find the FQIS blank, as he expected.
The all-metric 767 aircraft, new to the fleet, tracked fuel quantities in kilograms. After taking a dripstick measurement, Pearson converted the reading from centimetres to litres to kilograms. But he used the density figure for jet fuel from the Air Canada refueler's slip. This figure, used for all other aircraft in the fleet, stated the density in pounds/litre. The correct figure to use was for kilograms/litre, and the result actually calculated was incorrect. Since the FQIS was not operational, he entered the miscalculated result into the flight management computer. The airplane flew to Ottawa without accident, where another dripstick measurement was taken, and again, in the same way, converted incorrectly. Since the aircraft appeared to have enough fuel to reach Edmonton, no fuel was loaded at Ottawa.
While Flight 143 was flying over Red Lake, Ontario, at 41,000 feet (12,500 m) shortly after 8 pm CDT, 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, the pilots turned off the alarm, knowing that the engine could be gravity-fed in level flight. A few seconds later, the fuel pressure alarm also sounded for the right engine. This prompted the pilots to divert to Winnipeg.
The left engine failed within seconds, and the pilots 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 with the "all engines out" sound, a sharp "bong" that no one in the cockpit could recall having heard before. The right-side engine stopped seconds later, and the 767 lost all power. The aircraft then glided for 17 minutes without engine power. Flying with all engines out was never expected to occur, so it had never been covered in training. Adding to both the crew's and the controllers' problems, the plane's transponder failed, stopping the altitude reporting function and forcing the controllers to revert to primary radar to track the plane.
The 767 was one of the first airliners to include an electronic flight instrument system, which operated on the electricity generated by the aircraft's jet engines. With both engines stopped, the system went dead, and most screens went blank, leaving only a few basic battery-powered emergency flight instruments. While these provided sufficient information to land the aircraft, the backup instruments did not include a vertical speed indicator that could be used to determine how far the aircraft could glide.
On the Boeing 767, the control surfaces are so large that the pilots cannot move them with muscle power alone. Instead, hydraulic systems are used to multiply the forces applied by the pilots. Since the engines supply power for the hydraulic systems, in the case of a complete power outage, the aircraft was designed with a ram air turbine that swings out from a compartment located beneath the bottom of the 767 and drives a hydraulic pump to supply power to hydraulic systems.
In line with their planned diversion to Winnipeg, the pilots had been descending through 35,000 feet (10,700 m) when the second engine shut down. They had searched their emergency checklist for the section on flying the aircraft with both engines out, only to find that no such section existed. Captain Pearson was an experienced sailplane pilot, so he was familiar with flying techniques rarely used in commercial flight. Pearson needed to fly the 767 at the optimum glide speed to have the maximum range and, therefore, the largest choice of possible landing sites. 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 Quintal started to calculate whether they could reach Winnipeg. Quintal used the altitude from one of the mechanical backup instruments, while the distance travelled was supplied by the air traffic controllers in Winnipeg, measured by the aircraft's radar echo observed at Winnipeg. In 10 nautical miles (19 km; 12 mi), the aircraft lost 5,000 feet (1,500 m), giving a glide ratio of roughly 12:1. The optimal glide ratio for a Boeing 767-200 is roughly 20:1, achieved at speeds of 230–240 knots (430–440 km/h; 260–280 mph), and without payload. On dedicated sailplanes, glide ratios of up to 70:1 are possible.