23rd of July 1983

It was on this day in aviation history that the Air Canada Flight 143 would become known as the "Gimli Glider". Flight 143 was a Boeing 767-233 from Montreal to Edmonton via Ottawa, it ran out of fuel at an altitude of 41.00o feet, due to a fuel calculation error in combination with a faulty Fuel Quantity Indication System.

The aircraft after the forced landing at the Gimli Dragstrip

The Fuel Quantity Indication System of the Boeing 767 at that time was a dual channel unit, however, due to a design error, if one channel failed the whole system failed. Due to a breakdown in communication between several involved parties (Maintenance crew, Flight Crew, Refuelling, Operations) the aircraft was (illegally) dispatched with the fuel quantity gauges inoperative, Subsequently, the aircraft was refuelled using the dipstick in the tanks. Due to calculation errors, using a specific gravity figure for lbs/litre instead of kg/litre the crew entered the wrong fuel data in the FMS, which led them to believe they carried enough fuel. Another hole in the Swiss Cheese in this incident was the fact that the airline was in the process of changing the fleet over to Metric indications from Imperial Indications, this led to a mixed fleet of B767 with the airline, some were Metric, others Imperial. The density of the fuel delivered was 0.803 kg/l, the crew used a figure of 1.77 lbs/l as reported by the refueller. He was not aware that that the aircraft was using a metric FQIS.

They should have taken around 20.000 litres of fuel onboard but ended up only taking putting 4917 litres extra onboard. They thought they had 22.300 kg of fuel onboard, actually, this was 22.300 lbs.

Since the FQIS had failed the FMS did not receive updates on the fuel status the crew was unaware in flight that their fuel status was. During the stopover in Ottawa, the crew measured the fuel load again using the dipstick. That gave the crew a measured fuel load of 11.430 litres. This value was (again) converted using the wrong conversion resulting in a fuel load that was insufficient to reach their destination.

The full 208-page report from the Board of Inquiry can be found by clicking on the link below:

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