A quick tutorial on millibars & stuff for those who keep asking:

A Boeing 767 is normally fueled 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 airplanes, as a means of determining the total volume of fuel in the tanks. The dripstick measure indicated 11,525 litres.

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 weight instead of volume, which required a conversion in the measurements. The 767 measured fuel in kilograms, whereas all of the other manuals and planes in the Air Canada fleet used pounds. The pilots used an 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 figure, the 20,400 figure was entered into the airplane's computer, attempting to tell it that they had 20,400 pounds on board. Instead, the computer interpreted the figure as 20,400 kilograms and indicated that there was enough fuel based on the erroneous input. However, the airplane only had 9,144 kg (20,160 lb) onboard, too little for the flight to Edmonton.

Both the pilots and the fueling crew had misgivings about the math 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 re-measured before the flight proceeded to Edmonton.


At 41,000 feet 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 re-start 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!".