NYC00LA155 · Cessna 172R

After a normal pre-flight inspection and pre-takeoff engine check, the CFI and commercial pilot departed to practice some landings at nearby airports. The commercial pilot was flying, and both pilots described the flight to a local airport as uneventful. While turning onto the 'base leg' of the traffic pattern, at a power setting of 1,900 rpm, about 800 to 900 feet above ground level, the pilot attempted to increase engine power by moving the throttle forward; however, there was no response from engine. He then told the CFI 'there's no power.' The CFI confirmed that the throttle was unresponsive, and noticed that the engine rpm was slowly dropping. The CFI attempted to restart engine without success, and performed a forced landing to trees, which were located about 1/4 mile from the runway. Both pilots were wearing headsets, and said they did not hear any unusual noises or power changes prior to the loss of engine power. Examination of the wreckage did not reveal any pre-accident failures or malfunctions. The airplane had been operated for about 390 hours since new and was maintained under an approved manufacturer inspection program. Test-runs of the engine revealed a rich mixture operation in the idle and 400 pound airflow ranges, and an idle mixture rise of 120 rpm. Fuel flow checks of the fuel injector servo, flow divider, fuel nozzles and lines, revealed the flow divider and nozzles met new production test specifications and exhibited no unusual characteristics. Examination of the fuel servo did not reveal any physical malfunctions; however, a flow check of the fuel servo revealed a mixture that exceeded the rich test specification limits during several test points. Despite the rich mixture indication observed during testing, at no time was a loss of engine power experienced. The temperature and dewpoint reported at an airport about 18 miles south of the accident site, was 82 and 61 degrees F, respectively.

Verbatim NTSB analysis and probable cause from the NTSB dataset