Amateur-built T51 N154DF accident near Valkaria, Florida

Probable cause

The partial, then total, loss of engine power due to detonation and associated damage to several pistons as a result of an overly lean fuel-to-air ratio.

NTSB analysis

The pilot stated that, shortly after takeoff on a local test flight of the experimental, amateur-built airplane, the engine surged, with a corresponding fuel pressure fluctuation. Because the engine was developing partial power, he elected to return to the airport for landing, but while on the base leg of the airport traffic pattern, the engine lost total power. The airplane subsequently impacted a small retention pond and came to rest partially submerged in water. Postaccident examination of the engine revealed damage to the Nos. 2 and 5 cast aluminum pistons consistent with detonation. The fuel pumps and engine control unit were operationally tested with no discrepancies reported. Inspection of the cooling system components revealed no evidence of pre-impact failure or malfunction, and no evidence of warpage of the cylinder heads was observed.

The owner reported continuing engine overheating problems that occurred at sustained “moderate” power settings, which he was unable to correct despite extensive troubleshooting efforts including re-routing of the coolant reservoir. Although he believed he was operating the engine with a rich fuel-to-air ratio, when compared to an identical airplane that was operating successfully, the accident engine was being operated in a lean fuel-to-air ratio at all power settings (500 to 5,000 in 250 rpm increments). This finding was consistent with the pilot’s report of overheating at sustained moderate power settings.

Text from the NTSB. Open the NTSB docket for ERA19LA032 for the full record.