Narrative:

The preflight looked good [with the rental C152]; there were no noticeable leaks or discrepancies with the aircraft. The run up and magneto check was good. I got clearance to take off. The takeoff roll was normal. I rotated and climbed out at vy. Everything was fine until I reached around 300 feet AGL; [at] that time I noticed I was no longer climbing and that the airspeed was dropping as well as the vsi. The stall warning horn began to sound and I started extending flaps to transition into slow flight to keep from stalling. The engine was still running smoothly; however the engine was not producing enough power to maintain altitude. At this time tower asked me what was going on. I told them due to an unknown reason I was not able to maintain altitude and I was going to try to circle back and land. It did not look as though I would make it back to [the takeoff] runway and the tower advised that I could land on [a different] runway instead. I was able to make it down and land and the partial power I still had was enough to taxi back to [FBO] where I notified them of the events and issue with their plane.

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Original NASA ASRS Text

Title: C152 pilot reported engine was not producing normal power on takeoff and he was losing altitude; so he returned for an immediate landing.

Narrative: The preflight looked good [with the rental C152]; there were no noticeable leaks or discrepancies with the aircraft. The run up and magneto check was good. I got clearance to take off. The takeoff roll was normal. I rotated and climbed out at Vy. Everything was fine until I reached around 300 feet AGL; [at] that time I noticed I was no longer climbing and that the airspeed was dropping as well as the VSI. The stall warning horn began to sound and I started extending flaps to transition into slow flight to keep from stalling. The engine was still running smoothly; however the engine was not producing enough power to maintain altitude. At this time Tower asked me what was going on. I told them due to an unknown reason I was not able to maintain altitude and I was going to try to circle back and land. It did not look as though I would make it back to [the takeoff] runway and the Tower advised that I could land on [a different] runway instead. I was able to make it down and land and the partial power I still had was enough to taxi back to [FBO] where I notified them of the events and issue with their plane.

Data retrieved from NASA's ASRS site as of July 2013 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.