Welcome Guest. Sign in or Signup

2 Answers

Magneto Failure.

Asked by: 5345 views
Aircraft Systems, FAA Regulations, General Aviation, Private Pilot

Before departure i did the run up checklist in a cessna 172, testing the left magneto i noticed a drop in rpm if more than 125 rpm, y cleaned the magneto as i was tough (rpm to 2000 and leaning the mixture for a minute). Then testing it again it was within the limits. I departed an climbed to 8000 msl and did cruise checklist. On 2300 rpm and a light tailwind i noticed IAS didnt go higher than 80knots neither groundspeed. I tried leaning the mixture but it remained the same. Y ask for deviation to the departure airport and during descent at 1900 rpm engine had roughtness. Landed a tested the magneto and it was rought. Now i am thinking about it, if i did well, or what was the procedure, i said ATC what was happening but i am not sure if it is an emergency or a single incident if It needed to be notify.

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. Lucas on Jun 18, 2013

    In general filing a NASA form is never a bad idea, but in case I do not see the necessity. You did not declara an emergency for what I understand and in this type of case (even if you had declared) ATC might ask you to file a report if priority was given to you (and again this doesn’t seem to be the case). Also usually this happens a real busy airports (mostly class B) because if they need to hold a bunch of 747s, A340s, etc, they might need a piece of paper explaining why.
    All you didi was correct and in accordance with to the POH of a 172. Some higher performance airplanes the mixture needs to be leaned even during climb to a certain GPH.
    Being careful is never a bad idea on the other hand if you had continued going and trying to troubleshoot a possibly unsolvable problem could have proven dangerous if not fatal.
    So again in my opinion you did everything right.

    Lucas
    pilottrainingsolutions.com

    +2 Votes Thumb up 3 Votes Thumb down 1 Votes



  2. David Brown on Jul 15, 2013

    Lucas, all Normally Asirated engines need to be leaned in the climb. Just some POH’s are poorly written, in fact most are when it comes to this topic.

    The exception is those with an ACFP or Altitude Compensating Fuel Pump which is an option on some TCM engines and often found in Bonanza’s. These fuel pumps are configured to do the leaning for you. So these engines do require leaning, but they do it themselves!

    Things like the Rotax in LSA’s do it too.

    So no matter whether it is an O-320 or an IO-720 or anything else, including a Briggs and Stratton Lawn Mower engine will need the same leaning to keep the F/A ratio similar to that at rated power at sea level.

    The exceptions to this are turbo charged and turbo normalised engines as they think they are at sea level all the time so it is full rich or around 80dF LOP for them.

    Hope this helps.

    0 Votes Thumb up 0 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.