'Gimli Glider' is a nickname given to an aircraft involved in an infamous incident in
aviation history. On
23 July 1983, a
Boeing 767-200 jet,
Air Canada Flight 143, ran out of fuel at 41,000 feet (12 km) altitude about halfway through its flight from
Montreal 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.
The subsequent investigation revealed corporate failings and a chain of innocuous human errors which combined to defeat built in safeguards and deceive the Captain, Robert Pearson, into accepting an aircraft that should never have been allowed to fly.
History
On
22 July 1983, the day before the incident flight,
Air Canada Boeing 767 registration 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 41,000 feet (12,500 m) over
Red Lake,
Ontario, the
cockpit warning system chimed four times, 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 said that there was still plenty of fuel, 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 ever hearing before. The sound was the "all engines out" sound, an event that was never simulated during training.
[1] Seconds later the right side engine stopped too and the 767 lost all power, leaving the cockpit suddenly silent. In line with their planned divert to Winnipeg, the pilots were already descending to 28,000 feet when they ran out of fuel.
The jet engines generate
electrical power for the aircraft. The 767 was one of the first airliners to have an Electronic Flight Instrument System (
EFIS), which requires electricity to function; with the engines out, this system suddenly went dead, leaving only a few basic battery-powered standby analog flight instruments. One of the non-functioning electronic instruments was the
vertical-rate indicator, which would let the pilots know how fast they were sinking and therefore how far they could glide. However, the emergency standby flight instruments provided basic information sufficient to land the aircraft.
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 popped open on the underbelly of the aircraft. The forward velocity was sufficient to spin a propeller-driven generator which provided enough power to the hydraulics to make the aircraft 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.
By incredible good fortune 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. Copilot 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 travelled was supplied by the air traffic controllers in Winnipeg, who measured the distance as the aircraft's echo moved on their
radar screens. The aircraft 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 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 now 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. This gave passengers the sensation of plummeting sideways toward the ground. 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".
[2] 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 people gathered at the end of the
runway for Family Day.
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. The injuries were soon addressed by a doctor who was about to take off in an aircraft on Gimli's other runway, which was still being used by a flying club, the Air Cadet Gliding Center and
skydivers.
Coincidentally, and rather 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.
Investigation
The incident was subject to 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 which concluded that Air Canada management was responsible for "corporate and equipment deficiencies" whilst praising the flight and cabin crews for their "professionalism and skill".
[1] It noted that Air Canada "…neglected to assign clearly and specifically the responsibility for calculating the fuel load in an abnormal situation",
[1] finding that the airline had failed to reallocate the task of checking fuel load that had been the responsibility of the
flight engineer.
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 Office 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...”.
[5] This of course 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
Boeing 767 was still a very new aircraft, having flown its
maiden flight in September 1981. was the 47th
767 off the production line, delivered to
Air Canada less than 4 months previously.
[6] 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
MEL.
Refuelling
The incident occurred during a period when
Canada was converting to the
metric system. As part of this process the new 767’s being acquired by
Air Canada were the first to be calibrated for the new system and worked with
litres and
kilograms instead of
gallons and
pounds. All other aircraft were still operating with
imperial measurements. The pilot calculated a fuel requirement for the trip to
Edmonton 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 they 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 would normally have 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 a 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 required amount to reach their destination. Given the problems with the FQIS the Captain checked the calculations but was given the same incorrect conversion factor. All he did was check their math, 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 the
Air Canada internal investigation Captain Pearson was demoted for six months, First Officer Quintal suspended for two weeks and three maintenance workers also suspended.
[7] Both pilots however continued to work for Air Canada and in 1985 were awarded the first ever
Fédération Aéronautique Internationale Diploma for Outstanding Airmanship.
[8] was patched up at Gimli and flown out two days later. As of June 2007 C-GAUN is still in service with Air Canada.
Similar incidents
In
2000,
Hapag-Lloyd Flight 3378 landed in a powerless glide 500 meters short of the runway in
Vienna, Austria, with all aboard surviving; 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.
References
1. The 156-tonne Gimli Glider, , Merran, Williams, Flight Safety Australia, 2003
2.
3. The 156-tonne Gimli Glider, , Merran, Williams, Flight Safety Australia, 2003
4. The 156-tonne Gimli Glider, , Merran, Williams, Flight Safety Australia, 2003
5. Emergency, Crisis on the Flightdeck, , Stanley, Stewart, Airlife Publishing Ltd, 1992,
6.
7.
8.
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
External links
★
Gimli Glider write-up with 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
العربية
中国
Français
Deutsch
Ελληνική
हिन्दी
Italiano
日本語
Português
Русский
Español
