Narrative:

We were on a time-building VFR training flight. Along with the student and myself; the instructor; my [X] year old son was riding along in the back to total 3 souls on board. We were at 5;500 feet MSL. The engine appeared to be losing power. I advanced the throttle thinking it was due to the student struggling to maintain altitude. Shortly after I advanced the throttle I felt a knocking in my feet from the engine. I decided at that moment we would turn around and head for the nearest airport or landing strip. During the turn the power loss became significant. I then proceeded to trouble shoot the problem by executing our engine abnormality procedures. During the procedure I realized it was most likely a magneto malfunction and knew we would need to land immediately. We were already looking for safe places to put the airplane down. We decided on an unnamed gravel road east north east of [a highway].we executed an off airport landing without incident. There were no injuries to the souls on board nor was there damage to the aircraft. We made arrangements with the owner and the mechanic to come out and trouble shoot the issue and try and get the plane back in the air. During our wait the local police came and provided assistance to keep pedestrians and vehicles away from the airplane while we were waiting.once the mechanic and the owner arrived we eliminated the possible issues one by one. It ended up being an issue with the magnetos. They had a spare magneto on hand replaced the malfunctioning it and flew back to the airport without further incident.

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Original NASA ASRS Text

Title: C172 flight instructor reported a magneto failure and landing off-airport.

Narrative: We were on a time-building VFR training flight. Along with the student and myself; the instructor; my [X] year old son was riding along in the back to total 3 souls on board. We were at 5;500 feet MSL. The engine appeared to be losing power. I advanced the throttle thinking it was due to the student struggling to maintain altitude. Shortly after I advanced the throttle I felt a knocking in my feet from the engine. I decided at that moment we would turn around and head for the nearest airport or landing strip. During the turn the power loss became significant. I then proceeded to trouble shoot the problem by executing our engine abnormality procedures. During the procedure I realized it was most likely a magneto malfunction and knew we would need to land immediately. We were already looking for safe places to put the airplane down. We decided on an unnamed gravel road east north east of [a highway].We executed an off airport landing without incident. There were no injuries to the souls on board nor was there damage to the aircraft. We made arrangements with the owner and the mechanic to come out and trouble shoot the issue and try and get the plane back in the air. During our wait the local police came and provided assistance to keep pedestrians and vehicles away from the airplane while we were waiting.Once the mechanic and the owner arrived we eliminated the possible issues one by one. It ended up being an issue with the magnetos. They had a spare magneto on hand replaced the malfunctioning it and flew back to the airport without further incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.