Narrative:

We had taken off and were departing to the east on a right downwind when I noticed RPM loss abeam the numbers. I took control from my student and attempted a mixture control adjustment. The airplane lost most of its power and began shaking very violently. I immediately declared an emergency and was cleared to land back to the runway but had to inform tower I wouldn't make the runway but could make the parallel taxiway. I was then cleared to land on the taxiway and did so with no problems. I have no idea why the engine acted as it did.

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Original NASA ASRS Text

Title: C172 flight instructor reports engine failure during departure. Reporter took control from student; declared an emergency; and was able to glide back to a taxiway landing.

Narrative: We had taken off and were departing to the east on a right downwind when I noticed RPM loss abeam the numbers. I took control from my student and attempted a mixture control adjustment. The airplane lost most of its power and began shaking very violently. I immediately declared an emergency and was cleared to land back to the runway but had to inform tower I wouldn't make the runway but could make the parallel taxiway. I was then cleared to land on the taxiway and did so with no problems. I have no idea why the engine acted as it did.

Data retrieved from NASA's ASRS site as of April 2012 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.