Champion 7EC N80461 accident near Waunakee, Wisconsin

Probable cause

A total loss of engine power during the initial takeoff climb due to a worn manual fuel primer pump locking mechanism, which resulted in an unlocked primer and an overly rich fuel mixture.

NTSB analysis

The pilot purchased the airplane on the day of the accident and was planning to fly it to another airport. On the morning of the accident, a mechanic completed an annual inspection on the airplane. During the preflight inspection and the runup, no anomalies were noticed by the pilot.

During the initial takeoff climb, the pilot noticed a decrease in the engine rpm. The pilot was unable to maintain altitude, and he was unable to identify what caused the partial loss of engine power. Shortly thereafter, the engine sustained a total loss of engine power, and the pilot performed a forced landing. Upon touchdown to a residential road, the airplane impacted a tree and an unoccupied motor vehicle. The airplane came to rest upright in the rear of another unoccupied motor vehicle. The airplane sustained substantial damage to the right wing and the fuselage.

Postaccident examination of the airplane revealed significant wear of the locking mechanism on the manual fuel primer pump: only a narrow portion of the retaining lip was left to engage with the retaining pin. It is likely that a slight movement or vibration caused the retaining pin to move around the small piece of retaining lip that remained, resulting in the fuel primer pump becoming unlocked and extending. The spark plugs were found in a carbon fouled condition, consistent with an overly rich mixture.

The fuel primer pump position and the condition of the spark plugs indicate that the total loss of engine power was likely due to an overly rich mixture resulting from excess fuel being pulled through the fuel pump primer and into the engine’s intake system when power was applied.

Text from the NTSB. Open the NTSB docket for CEN23LA250 for the full record.