Welcome Guest. Sign in or Signup

1 Answers

First mag check attempt bad, second one good

Asked by: 2367 views ,
Aircraft Systems

During runup in a 172S, checked right mag and noted excessive RPM drop.  Pretty much immediately afterwards, went back to both mags, then back to right, and noted that the drop was within limits.  No throttle setting or mixture change during the switch.  Any explanations for why it seemed to fix itself?

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.

1 Answers



  1. Dave M on Apr 15, 2016

    Could have been carbon deposits on the plugs. Sometimes improperly burned fuel can muck up the plugs. On many airplanes, a solution to a excessively low mag drop is to run the engine lean, at a higer rpm for a number of minutes. This will usually burn off those deposits. It’s possible that when you went back to both, it was enough to remove whatever deposits there mght have been.

    +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.