Cessna 150L N19521 accident near Mesa, Arizona

Probable cause

A partial loss of engine power for undetermined reasons.

NTSB analysis

The engine lost partial power during the initial take off climb. The certified flight instructor (CFI) applied full carburetor heat and full rich mixture. The airplane did not produce enough power to maintain level flight, and the CFI landed the airplane straight ahead, colliding with trees. An inspection revealed a rubber-like material in the crankcase split line. The mixture control bottomed out before reaching the full idle stop. The spark plugs had dark sooty deposits, and the cylinder heads, piston tops, and valves all had slightly above-normal deposits. The engine ran without anomalies at different ranges of power during postaccident testing. The number one bottom spark plug, which was connected to the left magneto, did not produce a spark when the propeller was rotated by hand. The spark plug was dark and coated in oil. A compression test disclosed that the number four cylinder compression ring gaps were in the same location on the piston, causing blow-by and pressurization of the crankcase. There were also several cylinder base studs that were of an improper size.

Text from the NTSB. Open the NTSB docket for LAX08LA077 for the full record.