Gimli glider

Mobility Forum, Jan/Feb 2001 by Nelson, Wade H

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 fpm and marginally enough hydraulic pressure to control the ailerons, elevator, and rudder. Put veteran pilots Bob Pearson and cool-asa-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.

Flight 143's problems began on the ground in Montreal. A computer known as the "Fuel Quantity Information System Processor" or "FQIS" manages the entire 767 fuel loading process. The FQIS controls all of the fuel pumps and drives all the 767's fuel gauges. Little is left for the 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, later discovered to be due to a poorly soldered sensor. A one-in-a-million sequence of mistakes by Air Canada technicians investigating the problem managed to defeat the redundancy built into the system. This left Aircraft #604 without working fuel gauges.

In order to make their flight from Montreal to Ottawa, and on to Edmonton, Flight 143's maintenance crew resorted to calculating the 767's fuel load using a procedure known as "dripping" the tanks. "Dripping" might be compared to calculating the amount of oil in a car based on the dipstick reading. Among other things, the specific gravity of jet fuel is needed to make the proper drip calculations.

The flight crew had never been trained how to perform the drip 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 factor was written on the refueler's slip and was 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.

After a brief hop, Flight 143 landed in Ottawa. To be completely safe, Pearson insisted on having the 767 re-dripped. The refuelers reporting the plane as having 11,430 liters of fuel contained in the two wing tanks.

Pearson and Quintal, again using the same incorrect factor used in Montreal. calculated they had 20,400 kilos of fuel on board. In fact, they left for Ottawa with only 9144 kilos, roughly half what would be needed to reach Edmonton.

Lacking "real" fuel gauges, Quintal and Pearson manually keyed 20,400 into the 767's flight management computer. The flight management computer kept rough track of the amount of fuel remaining by subtracting the amount of fuel burned from the amount (they believed) they had started with. Their fate was now sealed.

According to Pearson, the crew and passengers had just finished dinner when the first warning light came on. Flight 143 was outbound over Red Lake Ontario at 41,000 feet and 469 knots at the time. The 767's "Engine Indicator and Crew Alerting System" (EICAS) beeped four times in quick succession, alerting them to a fuel pressure problem.

"At that point," Pearson says, "We believed we had a failed fuel pump in the left wing, and switched it off. We also considered the possibility we were having some kind of a computer problem. Our flight management computer showed more than adequate fuel remaining for the duration of the flight. We'd made fuel checks at two waypoints and had no other indications of a fuel shortage."

When a second fuel pressure warning light came on, Pearson felt. it was too much of a coincidence and made a decision to divert to Winnipeg. Flight 143 requested an emergency clearance and began a gradual descent to 28,000.

Says Pearson, "Circumstances then began to build fairly rapidly." The other left wing pressure gauge lit up, and the 767s left engine quickly flamed out.

The crew next tried crossfeeding the tanks. Pearson and Quintal immediately began making preparations for a one engine landing. Then another fuel light lit up. Two minutes later, just as preparations were being completed, the EICAS issued a sharp bong-indicating the complete and total loss of both engines. Says Quintal "It's a sound that Bob and I had never heard before. It's not in the simulator." After the "bong," things got quiet. Real quiet. Starved of fuel, both Pratt & Whitney engines had flamed out.

At 1:21 GMT, the forty million dollar, state-ofthe-art Boeing 767 had become a 132 ton glider. The APU, designed to supply electrical and pneumatic power under emergency conditions was no help because it ran off the same fuel tanks as the engines. Approaching 28,000 feet the 76?'s "Glass Cockpit" went dark. Pilot Bob Pearson was left with a radio and standby instruments, noticeably lacking a vertical speed indicator - the glider pilot's instrument of choice. Hydraulic pressure was falling fast and the plane's controls were quickly becoming inoperative. But the engineers at Boeing had foreseen even this most unlikely of scenarios and provided one last failsafe - the RAT.