Quick. What would you do if you determined that you had a leak in the right fuel tank of your airplane? In what position would you place the fuel selector? It’s sort of a trick question, but this has played a role in some spectacular neardisasters in airliners. Read on for the answer.
Ever heard of the Gimli Glider? That was an Air Canada Boeing 767 that took off in 1983 with far less fuel than it was supposed to have (thanks to an erroneous liters-to-gallons conversion) and glided to a successful landing in Gimli, Manitoba, following fuel exhaustion. How about Air Transat Flight 236 in 2001, an Airbus A330 that made a dead-stick landing in the Azores after experiencing a fuel leak while crossing the Atlantic? As is the case with many airliner incidents, a chain of events and bad decisions required these pilots to resort to heroics (and luck) to turn these events into successful outcomes. Of course, the point is to avoid needing heroism to save the day. Both crews were placed under extreme scrutiny for getting into such a predicament in the first place, but the blame wasn’t entirely on them.
In response to my opening question, if you answered, “switch to the left tank,” in most cases you’d be wrong. If you have a fuel leak in the right tank, you’d want to burn as much fuel out of it as possible, in order to preserve what you have in the remaining tank(s) to get
you to a suitable place to land. After all, if there are no airports nearby—such as when you’re crossing an ocean—you need all the fuel you have.
This was the case with the Air Transat flight. There was a massive leak in the fuel line feeding the right engine, and the crew decided to correct the imbalance by crossfeeding fuel from the good left tank to the leaking right one. Granted, it was a confusing situation, and the pilots were faced only with a warning that should have nothing to do with a fuel leak. Had the pilots been tracking actual fuel burn versus the planned fuel burn, however, the leak could have been discovered soon after it started. If that happened, and the pilots had cross-fed both engines from the leaking right tank—or simply shut down the right engine—the airplane would have landed in the Azores with power. Look up Air Transat Flight 236 for more information about this fascinating case.
A similar incident occurred to a colleague flying a Beechcraft Baron to Canada. The fuel gauge displaying the right auxiliary fuel tank quantity was dropping faster than the left’s. A glance at the right wing confirmed his suspicions when he saw wispy droplets of fuel at the trailing edge of the wing, indicating a sizable fuel leak. He made the right move by crossfeeding both engines from the leaking tank, quickly exhausting the supply and stopping the leak. High-octane fuel and the static electricity created by an airplane in flight set up a potential for a fire or explosion hazard.
The cause of the Baron incident was quickly discovered after the offending rubber fuel bladder was removed, revealing a leak caused by rubbing over the 20 years it had been installed. Why it chose that point to fail, only Murphy’s Law knows.
Rubber fuel bladders also can lead to a situation in which you may observe the fuel quantity gauge increasing as you fly. If a fuel vent clogs, the bladder begins to collapse, like one of those juice pouches that kids drink. As the engine sucks on the straw, so to speak, the bladder collapses and the float that provides quantity indication starts moving upward. Inside the wing, the collapsing fuel bladder—held in place by snaps or clips—begins pulling loose and shriveling up. If this goes too far, the bladder can be damaged beyond repair. In this case, obviously it’s best to switch to another tank and land. As a preventive measure, always preflight fuel vents to make sure they are not plugged.
For these reasons and more, it’s best to use common sense and continue to track fuel burn based on time. Today’s accurate fuel gauges may make pilots complacent to hacking a clock and comparing planned fuel burn to actual. But that’s a bad habit. Partly because of incidents like Air Transat, crews at my airline strictly check fuel at waypoints along the flight plan to confirm that planned and actual fuel are tracking closely. We also have very accurate fuel gauges, but the belt-and-suspenders approach is far better than the potential results of the aforementioned incidents.
The bottom line is that the airlines and professional flight crews rarely have fuel starvation or fuel exhaustion accidents, while general aviation pilots seem to routinely make headlines with such incidents. Sure, airliners have two pilots and much better equipment—but their pilots also use tried-and-true techniques to back up the fancy equipment.
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