Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.") It's part of what makes aviation so exciting for all of us... just when you think you've seen it all, along comes a scenario you've never imagined.

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Look for our daily Aero-Tips segments, coming each day to you through the Aero-News Network. Suggestions for future Aero-Tips are always welcome, as are additions or discussion of each day's tips. Remember... when it comes to being good pilots, we're all in this together.

Aero-Tips 02.18.06

This is it. I promise. But to be sure you really understand your airplane’s electrical system, try these last few questions. Answers are at the end of the article.

1. What should the ammeter, buss voltmeter and alternator loadmeter show during normal cruise flight?
2. Turn on something that uses a lot of electricity, like a landing light. What should each of the three gauges read? What happens when you turn the high-power item off?
3. Your alternator quits. What will the three gauges indicate?
4. You notice that the buss voltage reads 13 volts (in a 14 volt system) or 26 volts (28V airplane). What’s happening? What should the other two gauges indicate?

Answers

1. If everything’s running normally the ammeter will show about neutral, with neither a charge nor a discharge, the buss voltmeter will indicate 14 volts or 28V, as applicable, and the alternator loadmeter will typically run less than 50% of its rated output.
2. If you watched the gauges immediately when turning on the switch you’d see the ammeter begin to discharge while the buss voltmeter maintains 14V or 28V. The alternator loadmeter then shows an increase as it picks up the load, and if the system is capable the ammeter then charges before returning to neutral. Turn the item off and the reverse happens: an ammeter charge with a steady buss voltmeter, followed by an alternator loadmeter decrease before everything returns to normal indications (answer 1). In practice the ammeter needle may simply flicker unless a LOT of electricity is used.
3. Ammeter: discharge. Buss voltmeter: immediate drop to 12V or 24V, then a steady drop further. Alternator loadmeter: zero.
4. For some reason your alternator is not putting out full power. The ammeter may discharge and the alternator loadmeter likely reads low. Turn off nonessential equipment to conserve electricity, and consider landing as soon as practical.

Please note: This "water visualization" is not technically correct -- but it does a superb job of helping pilots comprehend what’s going on with the electrical system to accurately monitor it and troubleshoot problems…as you’ve probably seen by your ability to answer these questions. Engineers, mechanics and purists, please forgive this teaching tool.

Aero-tip of the day: Familiarity with the electrical system and its indicators lets you understand when it’s working... and when it’s not. To be safe, actively monitor the electrical system.

FMI: Aero-Tips