Gimli Glider

Gimli Glider is a nickname given to an aircraft involved in an infamous incident in aviation history. On July 23, 1983, /ship 604, a Boeing 767-200 jet, Air Canada Flight 143, ran out of fuel at 40,000 feet (12 000 m), about halfway through its flight from Ottawa to Edmonton. The crew was able to glide the aircraft safely to a forced landing at Gimli Industrial Park Airport, a former airbase at Gimli, Manitoba.

History

Fuel miscalculation

A Boeing 767 is normally fuelled using a device known as the Fuel Quantity Information System Processor (FQIS), which operates all of the internal pumps and reports to the pilots on the status of the fuel load. However, Flight 143's FQIS was not working properly, a problem later traced to a bad solder joint in the capacitance gauges in the fuel tanks. Instead, the fuel load was measured with a dripstick, a dipstick for aircraft, as a means of determining the total volume of fuel in the tanks. The dipstick measure indicated 11 525 L.

The error occurred when it came time to calculate how much fuel was needed for the flight from Montreal to Edmonton. The calculations were based on weight instead of volume, which required a conversion in the measurements. The incident aircraft was the first 767 in the Air Canada fleet that measured fuel in kilograms, whereas all of the other manuals and planes in the Air Canada fleet used pounds. The pilots used a unit conversion factor of 1.77 lb/L. However, a fuel load measured in kilograms should have used the conversion factor of 0.8 kg/L. After using the 1.77 factor, the figure 20,400 was entered into the aircraft's computer, attempting to tell it that they had 20,400 pounds of fuel on board. Instead, the computer interpreted the figure as 20 400 kilograms and indicated that there was enough fuel based on the erroneous input. In fact, the aircraft only had 9144 kg (20,160 lb) onboard, too little for the flight to Edmonton.

Both the pilots and the fuelling crew had misgivings about the arithmetic and calculated the figures three times. After coming up with the same number the pilot, Captain Robert (Bob) Pearson, finally stated, "That's it, we're going." Flight 143 then flew the short distance from Montreal to Ottawa, where the fuel level was remeasured before the flight proceeded to Edmonton.

Running out of fuel

At 41,000 feet (12 497 m) over Red Lake, Ontario, the cockpit warning system chimed four times and indicated a fuel pressure problem on the left side. The pilots thought a fuel pump had failed and turned it off; the tanks are above the engines so gravity will feed them without the pumps. The computer said that there was still plenty of fuel, but this was based on calculations using the assumption that the plane had started with 20 400 kg of fuel. 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 one-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 ever hearing before. The sound was the "all engines out" sound, an event that was never simulated during training. Seconds later the right side engine stopped and the 767 lost all power leaving the cockpit suddenly silent and allowing the cockpit voice recorder to easily pick out the words "Oh, fuck!".

The 767 is based on a "glass cockpit" concept in which mechanical instruments are replaced with display screen monitors. The jet engines also delivered electrical power to the aircraft, so most of the instrumentation suddenly went dead. One of the lost instruments was the vertical-rate indicator, which would let the pilots know how fast they were sinking and therefore how far they could glide.

The engines also supplied power to the hydraulic systems, without which a plane the size of the 767 could not be controlled. However, Boeing actually planned for this possible failure and included a device known as a ram air turbine that automatically popped open on the side of the plane, using some of the plane's residual velocity to spin a propeller-driven generator and provide enough power to the hydraulics to make it controllable.

Landing at Gimli

The pilots immediately opened the emergency guide looking for the section on flying the aircraft with both engines out, only to find that no such section existed. Pearson glided the plane at 220 knots (407 km/h), his best guess as to the optimum airspeed. Copilot Maurice Quintal began making calculations to see if they would reach Winnipeg. He used the altitude from one of the mechanical backup instruments, while the distance travelled was supplied by the air traffic controllers in Winnipeg, who measured the distance the plane's echo moved on their radar screens. The plane had lost 5,000 ft in 10 nautical miles (1.5 km in 19 km) giving a glide ratio of approximately 12:1. The controllers and Quintal both calculated that Flight 143 would not make 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, Gimli had become a public airport, and had decommissioned one of its parallel runways, which was now being used for road 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 Quintal did a power-off "gravity drop" of the main landing gear, but the nose wheel, despite being built to open by swinging backwards with the force of the wind, would not lock. The ever-reducing speed of the plane also reduced the effectiveness of the ram air turbine, and the plane became increasingly difficult to control. As they grew nearer it became apparent that they were too high, and Pearson executed a manoeuvre known as a "forward slip" to increase their drag and reduce their altitude. This gave passengers on one side of the aircraft the sensation of plummeting sideways toward the ground. Forward slips are commonly used with gliders and light powered aircraft in the same situation. Here, Pearson's experience as a glider pilot became useful. As soon as the wheels touched the runway, he "stood on the brakes", blowing out several of the plane's tires. The plane came to rest, in a nose-down position due to the unlocked nose gear, only a few hundred feet from Family Day at the end of the runway.

None of the 61 passengers was 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 hanging almost vertically. 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. The injuries were soon addressed by a doctor who was about to take off in a plane on Gimli's other runway, which was still being used by a flying club and skydivers.

Aftermath

Mechanics soon repaired the minor damage, and the plane was flown out two days later. Within weeks it was fully repaired and back in service. Ironically, the mechanics sent from Winnipeg Airport in a van ran out of fuel on their way to Gimli and found themselves stranded. Another van was sent to pick them up.

Moreover, when failure of both engines was tested in the simulator after the incident, no-one was able to perform a successful landing.

The "Gimli Glider", registration C-GAUN, (Fin 604, on the nose gear door or top of the tail, hence Fin number) is still in service with Air Canada as of 2006.

An exceptionally detailed account of the incident including the technical/engineering failures involved as well as the emotional human story of the crew and passengers was documented in a book Freefall: From 41,000 Feet to Zero - a True Story by William and Marilyn Hoffer (ISBN 0671696890, published by Simon & Schuster September 18, 1989).

In Western Canadian slang, "to pull a Gimli Glider" is to make a spectacular foul-up.

In 1995, a television movie was released: Flight 174. It took many liberties from the actual incident, including the name of the airline and the flight number.

Similar incidents

A similar incident involving a Canadian airline is Air Transat Flight 236 in 2001, which involved an emergency landing without fuel. Hapag-Lloyd Flight 3378 ended with a powerless glide as well.

External links

Gimli Glider write-up with photo & links
-- TV movie loosely based on this event
CBC Story and Video
Photo of C-GAUN after the landing
Pictures (airliners.net)
GIMLI Detailed recollections on the Alt.Disasters.Aviation FAQ

1983 | Fuel exhaustion on commercial airliners | History of Manitoba | Metrication | Notable aircraft