Passengers of Flight 143 Learn the Importance of Units

Background

On July 23, 1983 Air Canada Flight 143 was en route to Edmonton from Montreal when something went terribly wrong!  A panel light blinked accompanied by a warning buzzer indicated that there was a problem with the left forward fuel pump.  The pilot hoped that it had simply failed since normal flight would still be possible.  But a few seconds later, his worst fear was confirmed.  A second pump in the left wing was also failing.  This almost certainly meant that the tanks were running out of fuel while cruising at 26,000 feet!  So that we can get to the heart of the problem, I'll tell you that thanks to an incredibily skilled pilot, all 61 passengers and crew survived the crash landing.

So what happened?

The nagging question is: "How in the world does a jet run out of fuel at 26,000 feet?"  Firstly, there was no fuel leak or other engine malfunction.  The hard truth is that the ground crew simply did not put enough fuel into the plane before it departed.  Let's see how this happened!

1.  A maintenance worker found that the fuel gauge did not work on ground inspection.  He incorrectly assured the pilot that the plane was certified to fly without a functioning fuel gauge if the crew checked the fuel tank levels.

2.  Crew members measured the 2 fuel tank levels at 62 cm and 64 cm.  This corresponded to 3758 L and 3924 L for a total of 7682 L according to the plane's manual.  (Notice that the Canadian government was introducing the metric system nationwide)

3.  The ground crew knew that the flight required 22,300 kg of fuel.  The problem they faced was with 7,682 L of fuel on the plane, how many more liters were needed to total 22,300 kg of fuel?

4.  One crew member informed the other that the "conversion factor" (being the fuel density) was 1.77.  THE CRUCIAL FAULT BEING THAT NO ONE EVER INQUIRED ABOUT THE UNITS OF THE CONVERSION FACTOR.  So it was calculated that the plane needed an additional 4,917 L of fuel for the flight.

What the ground crew did

7,682 L x 1.77 = 13,597 kg of fuel on board

22,300 kg needed - 13,597 kg on board = 8,703 kg to be added

8,703 kg / 1.77 = 4,916 L of fuel to be added

What caused the problem?

The metric changeover in Canada should have been accompanied by further education on the airline's part.  The "conversion factor" of 1.77 was actually the fuel's density in pounds per liter, not kilograms.  The fuel's density in kilograms per liter is 0.803.

What the ground crew should have done

7,682 L x 0.803 kg/L = 6169 kg of fuel on board

22,300 kg needed - 6,169 kg on board = 16,131 kg to be added

16,131 kg / 0.803 kg/L = 20,163 L of fuel to be added

The Bottom Line

By not accounting for the units in the density of the fuel, the ground crew added 4,916 L of fuel to a plane that needed 20,163 L of fuel and nearly killed over 60 people!  Still think units aren't really important???