Gimli Glider

Gimli Glider is the nickname of an Air Canada aircraft which was involved in an infamous aviation incident. On 23 July 1983, a Boeing 767-200 jet, Air Canada Flight 143, ran completely out of fuel at 41,000 feet (12,000m) altitude, about halfway through its flight from Montreal to Edmonton. The crew was able to glide the aircraft safely to an emergency landing at Gimli Industrial Park Airport, a former airbase at Gimli, Manitoba. ^[1] The subsequent investigation revealed corporate failures and a chain of minor human errors which combined to defeat built-in safeguards. In addition, fuel loading was miscalculated through misunderstanding of the recently adopted metric system.

History

On 22 July 1983, the day before the incident flight, Air Canada's Boeing 767 (registration C-GAUN) 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 via Ottawa to Edmonton, with Captain Robert (Bob) Pearson and First Officer Maurice Quintal at the controls.

Running out of fuel

At 12,500 m (41,000 feet) over Red Lake, Ontario, the cockpit warning system sounded, indicating a fuel pressure problem on the left side. The pilots assumed that a fuel pump had failed, and turned it off; the tanks are above the engines, so gravity would feed them without the pumps. The computer stated that there was still sufficient fuel for the flight, but this was based on mismatched calculations (see Refuelling below). A few moments later a second fuel pressure alarm sounded, and the pilots decided to divert to Winnipeg. Within seconds the left engine failed and they prepared for a single-engine landing. While they attempted to restart the engine and communicate with controllers in Winnipeg for an emergency landing, the warning system sounded again, this time with a long "bong" that no one present could recall having heard before. This was the "all engines out" sound, an event that was never simulated during training.^[2] 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. In line with their planned divert to Winnipeg, the pilots were already descending through 28,000 feet when they ran out of fuel. The jet engines generate electrical power for the aircraft, and the 767 was one of the first airliners to have an Electronic Flight Instrument System (EFIS), requiring electricity to function. With both engines inoperative, this system suddenly went dead, leaving only a few basic, battery-powered, standby analog flight instruments. While the emergency instruments provided basic information sufficient to land the aircraft, one of the non-functioning electronic instruments was the vertical-rate indicator, which would have let the pilots know how fast they were sinking, and therefore how far they could glide. The engines also supply power for the hydraulic systems, without which an aircraft the size of the 767 cannot be controlled. However, aircraft designs are required to accommodate such a failure, and a ram air turbine automatically deployed on the underbelly of the aircraft. In theory, the forward velocity of the aircraft would spin the ram air turbine, a propeller-driven generator, providing enough power for the hydraulics to make the aircraft controllable, although this proved problematic during landing.

Landing at Gimli

The pilots immediately searched their emergency checklist for the section on flying the aircraft with both engines inoperative, only to find that no such section existed.^[3] However, Captain Pearson was an experienced glider pilot. This gave him familiarity with some flying techniques almost never used by commercial pilots. He realized that, in order to reduce their rate of descent as much as possible, he needed to fly the 767 at a speed known as the "best glide ratio speed". He flew the aircraft at 220 knots (407 km/h), his best guess as to this airspeed. 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 ft in 10 nautical miles (1.5 km in 18½ km) 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 selected his former RCAF base at Gimli as the landing spot. Unbeknownst to Quintal, since his time in the service, RCAF Station Gimli had become a public airport, and had decommissioned one of its parallel runways, which was then being used for sports car racing. Furthermore, on this particular day the area was covered with cars and campers for "Family Day", and a race was being run on the former runway. As they approached Gimli, the pilots attempted a power-off gravity drop of the main landing gear, but the nose wheel failed to lock down due to a hydraulic lock (the nose wheels are blown back by the airflow). The ever-reducing speed of the aircraft also reduced the effectiveness of the ram air turbine, and the aircraft became increasingly difficult to control. As they grew nearer it became apparent that they were too high, and Pearson executed a maneuver known as a forward slip to increase their drag and reduce their altitude. As Pearson executed the slip, the aircraft was flying over a golf course, and one passenger reportedly said, "Christ. I can almost see what clubs they're using".^[3] A slip is commonly used with gliders and light aircraft, either to lose height quickly or to execute a cross-wind landing. As soon as the wheels touched the runway, Pearson "stood on the brakes", blowing out several of the aircraft's tires. The unlocked nose wheel collapsed and was forced back into the housing causing the nose section to scrape along the ground. The aircraft came to rest only a few hundred feet from the crowd of families gathered at the end of the runway. None of the 61 passengers were hurt during the landing, although there were some minor injuries when exiting via the rear slide which, owing to the raised elevation of the tail, was deployed at a steeper than usual angle. A minor fire in the nose area was soon put out by racers and course workers on the ground who rushed over with fire extinguishers, and the injuries were addressed by a doctor who had been about to take off in an aircraft on Gimli's other runway, which was still being used by the Air Cadet Gliding Center flying club and skydivers. Mechanics were sent from Winnipeg Airport; their van ran out of fuel on the way to Gimli, leaving them stranded.^[4] Another van was sent to pick them up.

Investigation

The incident was the subject of an immediate investigation by Air Canada, which 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".^[5] It noted that Air Canada "… neglected to assign clearly and specifically the responsibility for calculating the fuel load in an abnormal situation"^[6], 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.

Fuel Quantity Indicator System

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 dripstick 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 whilst 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 dripstick. In a misunderstanding however the pilot believed that the aircraft had been flown with the fault from Toronto the previous afternoon. The 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 Maurice 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. Whilst 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 dripstick 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...”.^[7] 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.^[8] 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 practise 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.

Refuelling

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 English measurements. For the trip to Edmonton, the pilot calculated a fuel requirement of 22,300 kg. A dripstick check indicated that there were 7,682 litres already in the tanks. In order to calculate how much more fuel had to be uplifted 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 quantity. (This task had previously been completed by the Flight Engineer, but the 767 was the first of a new generation of airliners operated by two flight crew and the Flight Engineer position had been made redundant.) A litre of jet fuel weighs 0.803 kg, so the correct calculation was: 7682 litres x 0.803 = 6169 kg
22300 kg – 6169 kg = 16131 kg
16131 kg ÷ 0.803 = 20163 litres 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 x 1.77 = 13597 ‘kg’
22300 kg – 13597 ‘kg’ = 8703 kg
8703 kg ÷ 1.77 = 4916 litres 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, the Captain 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 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 whilst there. In converting the quantity to kilograms, the same incorrect conversion factor was used. Believing they now had 20,400 kg of fuel, they still only had less than half the amount they actually needed.

Aftermath

The Gimli Glider, flying into Toronto in July 2005.

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.^[9] However, both pilots continued to work for Air Canada, and in 1985 were awarded the first ever Fédération Aéronautique Internationale Diploma for Outstanding Airmanship.^[10] C-GAUN was patched up at Gimli and flown out two days later. It remains in service with Air Canada almost a quarter century later, but is scheduled to be retired in December, 2007.^[11]

Similar incidents

In 2000, Hapag-Lloyd Flight 3378 landed in a powerless glide 500 metres short of the runway at Vienna International Airport in Wien-Schwechat, the airport of Vienna. All aboard survived; again the cause was misleading information from the Flight Management System. In 2001, Flight 236 of Air Transat, another Canadian airline, safely made an emergency landing in the Azores without fuel; in this case the cause was a fuel leak. The aircraft involved was an Airbus A330-243 (reg. C-GITS, cn 271), and it was the first fly-by-wire commercial aircraft in the world to make a successful "all engines out" landing.

References

Further reading

• Emergency, Crisis on the Flight Deck, Stanley Stewart, Airlife Publishing Ltd., 1992, ISBN 1 85310 348 9
• Freefall: From 41,000 feet to zero - a true story, William and Marilyn Hoffer, Simon & Schuster, 1989 ISBN 978-0671696894

See also

• Falling from the Sky: Flight 174, TV movie loosely based on this event

External links

• Gimli Glider write-up with links
• CBC Story and Video
• Photo of C-GAUN after the landing
• Pictures (airliners.net)
• GIMLI Detailed recollections on the Alt.Disasters.Aviation FAQ

Coordinates: 50°37′44″N 97°02′38″W / 50.62889, -97.04389