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Redundancy in Aviation

Friday, September 5, 2008

Aviation is full of redundancy.

Your airplane may have only a single engine, but that one engine has dual, redundant systems for fuel, air, and ignition.

The next time you do a run-up, consider that you’re testing the primary and backup for each of these systems.

Magneto check? You're testing each one of the two independent ignition systems: two separate magnetos, driving two separate sets of spark plugs.

Carb-heat? You're testing an alternate source of air into the engine.

If you're in a high-wing airplane, gravity will force fuel into the engine, and that's pretty fail-safe. But notice that you have two fuel tanks.

If you're in a low-wing airplane, you'll have an auxiliary, electrically driven, fuel pump in addition to the engine-driven fuel pump.

All this redundancy doesn't make the engine twice as reliable: it makes it thousands of times more reliable.

A pilot with good judgment would never intentionally remove any one part of a redundant system. Before take-off, the run-up proves to the pilot that both halves of that critical engine system works.

Redundancy in Instrument Flying

Private pilots are taught attitude instrument flying (hood time!) and then are told that it is illegal and unsafe to fly into clouds. The attitude instrument flying experience, and that artificial horizon, is the pilot's backup.

Should a non-instrument-rated pilot blunder into a cloud, the attitude indicator can be used to do a smooth 180-degree turn back to good weather. At the worst, the attitude indicator keeps the airplane upright while the pilot calls for help.

But, if a non-instrument-rated pilot intentionally flies into clouds, all faith is being placed on a single instrument: an instrument which can fail as often as every 500 hours.

Instrument-rated pilots do have a backup: your turn-coordinator and all that partial panel training.

Vacuum pumps and magnetos have about the same failure rate. So consider a partial-panel practice instrument approach as the philosophical equivalent to a run-up.