Narrative:

My instrument student obtained a VFR clearance for a mesa local departure. Runup was normal with temperatures and pressures in the green. The engine was properly leaned and magnetos checked ok. We then taxied onto runway 19R and were cleared for takeoff. The initial takeoff roll, rotation and climb were normal. At approximately 100-150 ft the engine began sputtering and running very rough and appeared to be about to fail completely. I took the controls from the student and executed an immediate right 180 degree emergency return. I announced to tower that we needed to make an emergency return and received a clearance to land on runway 1L. We continued under partial power and landed without incident. The source of the problem was most likely a magneto failure or fouled plugs. Postflt inspection did not reveal any obvious cause. My decision to make an emergency return was proper and any deviation from our departure clearance was inadvertent.

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Original NASA ASRS Text

Title: C172 JUST AFTER LIFTOFF THE ENG LOST PWR AND BECAME VERY ROUGH. INSTRUCTOR ASSUMED CTL, DECLARED AN EMER, AND TURNED BACK TO THE ARPT.

Narrative: MY INST STUDENT OBTAINED A VFR CLRNC FOR A MESA LCL DEP. RUNUP WAS NORMAL WITH TEMPS AND PRESSURES IN THE GREEN. THE ENG WAS PROPERLY LEANED AND MAGNETOS CHKED OK. WE THEN TAXIED ONTO RWY 19R AND WERE CLRED FOR TKOF. THE INITIAL TKOF ROLL, ROTATION AND CLB WERE NORMAL. AT APPROX 100-150 FT THE ENG BEGAN SPUTTERING AND RUNNING VERY ROUGH AND APPEARED TO BE ABOUT TO FAIL COMPLETELY. I TOOK THE CTLS FROM THE STUDENT AND EXECUTED AN IMMEDIATE R 180 DEG EMER RETURN. I ANNOUNCED TO TWR THAT WE NEEDED TO MAKE AN EMER RETURN AND RECEIVED A CLRNC TO LAND ON RWY 1L. WE CONTINUED UNDER PARTIAL PWR AND LANDED WITHOUT INCIDENT. THE SOURCE OF THE PROB WAS MOST LIKELY A MAGNETO FAILURE OR FOULED PLUGS. POSTFLT INSPECTION DID NOT REVEAL ANY OBVIOUS CAUSE. MY DECISION TO MAKE AN EMER RETURN WAS PROPER AND ANY DEV FROM OUR DEP CLRNC WAS INADVERTENT.

Data retrieved from NASA's ASRS site as of July 2007 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.