Cessna 172 N20747 accident near Englewood, Colorado

Probable cause

A partial loss of engine power due to fuel-oil contamination of the fuel injection servo.

NTSB analysis

While performing touch-and-go landings, the flight instructor and student pilot noticed a partial loss of engine power on climbout, about 200 ft above ground level (agl). The flight instructor reported the tachometer read 2,100 and then 1,600 rpm. During a forced landing to a golf course, the airplane’s nose landing gear collapsed and the airplane came to rest inverted.

A postimpact test of the engine’s fuel injection servo found fuel flow below the minimum service limit at most test points. When the servo was disassembled, a thick blue liquid consistent with a fuel-oil mixture was found in the venturi chambers. Oil residue was noted in the hex plug and air diaphragm, the spring and stem assembly, and the air passage to the air diaphragm. No other anomalies were detected with the engine.

A service bulletin from the fuel injection servo manufacturer states that this type of contamination could cause an engine to exhibit “gradually deteriorating idle, difficulty starting and/or cold engine acceleration performance.” The flight school was aware of the service bulletin and was inspecting airplanes that had the engine symptoms listed in the service bulletin.

It is likely that contamination of the fuel injection servo resulted in a partial loss of engine power and subsequent forced landing.

Text from the NTSB. Open the NTSB docket for CEN24LA350 for the full record.