Welcome Guest. Sign in or Signup

2 Answers

Engine Driven Alternator

Asked by: 3726 views Aircraft Systems

we say Engine driven alternator.

until engine is shut down, alternator runs automatically.

but, there is a alternator switch in the cockpit.

why do we shut off and turn on that switch?

why that switch need for airplane?

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

2 Answers

  1. Best Answer


    John D. Collins on Mar 17, 2013

    Good question. I leave my alternator switch on all the time. Cars don’t have an alternator switch, but seem to have reliable operation. When the engine starts, the voltage regulator is commanding the alternator to increase its voltage output and the field current is at a maximum. The thought is that when the starter is disengaged, there will be a short term voltage spike until the regulator is able to adjust it back to a normal voltage and the voltage spike will adversely affect electrical circuits that are on. However, the battery is in the circuit and acts as a very large capacitor which prevents spikes in the voltage. I have been starting my airplane for 34 years with the alternator switch left on without adverse effect.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  2. Bill Trussell on Mar 19, 2013

    Having had more than one alternator failure in my flying career I can offer that the switch in the cockpit is provided in order to more totally isolate the alternator from the electrical system in the event of a failure. This maximizes battery endurance and affords you a chance to get on the ground before everything does dark.

    Think of it as being similar to the “off” position on the fuel selector. When the power fails and fuel is no longer needed, turn it off (in this case for safety reasons).

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.