September 4, 2004

The Gimli Glider (or why units matter...)

The Braden Files links to an aviation story with an amazing outcome: bq. If a Boeing 767 runs out of fuel at 41,000 feet what do you have? Answer: A 132 ton glider with a sink rate of over 2000 feet-per-minute and marginally enough hydraulic pressure to control the ailerons, elevator, and rudder. Put veteran pilots Bob Pearson and cool-as-a-cucumber Maurice Quintal in the cockpit and you've got the unbelievable but true story of Air Canada Flight 143, known ever since as the Gimli Glider. bq. Flight 143's problems began on the ground in Montreal. A computer known as the Fuel Quantity Information System Processor manages the entire 767 fuel loading process. The FQIS controls the fuel pumps and drives all of the 767's fuel gauges. Little is left for crew and refuelers to do but hook up the hoses and dial in the desired fuel load. But the FQIS was not working properly on Flight 143. The fault was later discovered to be a poorly soldered sensor. An improbable sequence of circuit-breaking mistakes made by an Air Canada technician independently investigating the problem defeated several layers of redundancy built into the system. This left Aircraft #604 without working fuel gauges. And the units in question: bq. The flight crew had never been trained how to perform the calculations. To be safe they re-ran the numbers three times to be absolutely, positively sure the refuelers hadn't made any mistakes; each time using 1.77 pounds/liter as the specific gravity factor. This was the factor written on the refueler's slip and used on all of the other planes in Air Canada's fleet. The factor the refuelers and the crew should have used on the brand new, all-metric 767 was .8 kg/liter of kerosene. No fatailities -- the photo of the 767 sitting nose-down on the race car track is quite a starteling one... Posted by DaveH at September 4, 2004 9:38 AM