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Surviving Instrument Failure

Instrument pilots routinely bet their lives on the gauges and even VFR pilots depend on the instruments at times, especially at night...Instrument pilots routinely bet their lives on the gauges and even VFR pilots depend on the instruments at times, especially at night... so how can you survive when your instruments lie?

Survival Tip #1: Know Your Instruments
Some of your flight instruments are powered by pneumatics (from vacuum or pressure pumps). Others are run by electricity. Still more reference air pressure, through the static port(s) and pitot tube. You need to know -- instantly and without question -- what powers each flight instrument in the airplane you're piloting and it may differ from airplane to airplane. ...most heading indicators are pneumatic, but some are electric. ...most horizontal situation indicators (HSIs, commonly found in high-performance singles and twins) are electric, but a few on the market are vacuum-driven. ...most vertical speed indicators (VSIs) are pitot/static, but instantaneous VSIs are electric. Only by knowing what powers each instrument in the airplane you are flying can you move on to step #2.

Survival Tip #2: Know How to Tell Which Instrument is Lying
To properly identify a failed instrument, you need to know:

  1. what powers the suspect instrument (Tip #1 above), and
  2. which other instruments give you similar information but are powered differently.
With these two pieces of information, you can use two instruments to overrule a bad indication from a third.

How: If wings-level on the attitude indicator results in an indicated turn on the electric turn coordinator, then one or the other is lying. If you suspect (or guess) vacuum instrument failure and your attitude and heading indicators are pneumatic, you can hold wings level by referencing the attitude indicator and check your electric turn coordinator or turn-and-bank. If the electric instruments indicate a turn, quickly check your magnetic compass. If the compass shows a turn (beware of magnetic compass errors here, folks), then two instruments (turn coordinator and compass) using independent power sources have overruled a third (attitude, or heading indicator, whichever you re using for the check). Make your determination quickly or you will be in trouble, quickly. Only with practice can you make the identification of a failed instrument, so get some simulator time ... and then you'll be ready for-

Survival Tip #3: Cover the Dead Instrument
A failed instrument will distract you, beyond belief. Always carry sticky notes or one of those soap dish instrument covers, and use it on any instrument you've identified as dead. Now, it won t assault your eyes with its lies, and you can get on to-

Survival Tip #4: Declare an Emergency
Don t be a hero. When you use the 'E' word, ATC will drop everything to get airplanes out of your way. If you don t declare, you may be given heading or altitude changes to avoid other traffic and the more you maneuver, the more likely you'll lose control. Declaring an emergency gives you priority and it will make your life significantly easier. Do it.

Now that you've got the failed instruments identified and have declared ownership of the sky, we're ready to get on with the business of flying the crippled craft home -- next week...

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About This Author:
Tom Turner is a widely published author and regular forum speaker at EAA's Oshkosh/Airventure and American Bonanza Society. Tom holds an M.S. in Aviation Safety with an emphasis on pilot training methods and human factors. He has worked as lead instructor at FlightSafety International, developed and conducted flight test profiles for modified aircraft and authored three books including: Cockpit Resource Management: The Private Pilot's Guide and Instrument Flying Handbook (both from McGraw-Hill). His flight experience currently spans 3000 hours with approximately 1800 logged as an instructor. Tom's certificate currently shows ATP MEL with Commercial/Instrument privileges in SEL airplanes.
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