Aero Vodochody L-39ZA N343WT accident near Barnhart, Texas

Probable cause

A total loss of engine power due to water-contaminated fuel from an undetermined source.

NTSB analysis

The pilot stated that after taking off and climbing through about 7,300 ft mean sea level (msl), he heard a “pop” noise. He scanned the engine instruments and saw them “rolling back.” The pilot pitched the airplane for best glide and attempted to restart the engine, which was unsuccessful. Unable to restart the engine, the pilot performed a forced landing to a dirt road in a field, which resulted in substantial damage to both wings. The pilot reported that he had flown to the departure airport the day before the accident, had the airplane refueled with 342 gallons of fuel, and had the airplane secured in a hangar before taking off for the accident flight.

A postaccident examination of the airplane and engine revealed no mechanical anomalies with the engine or airframe that would have contributed to a loss of engine power. Fuel recovered from the airplane fuel sump after the accident was tested for contaminants. Water was detected in that fuel sample at a rate of 55 parts per million (ppm), which is considered an acceptable level. However, recovery personnel stated that when the airplane was de-fueled during the recovery process, the ½ gallon capacity fuel-water separator filter clogged and filled with water 3 times. The recovery personnel further stated the airplane had not been rained on after the accident and before recovery.

Fuel was tested from the source where the airplane was refueled before the accident flight and water was detected at less than 15 ppm and no fuel related issues were reported by the operators of the other aircraft refueled from the same source.

Fuel is capable of absorbing water directly from the atmosphere via the ventilation system of the fuel system/storage tank or through condensation in the tank. However, investigators were not able to verify if that occurred.

The circumstances of the accident, coupled with the finding of undissolved water in the fuel during the recovery of the airplane, is consistent with a total loss of engine power due to fuel contamination. However, the source of the water in the fuel could not be determined based on available evidence.

Text from the NTSB. Open the NTSB docket for WPR23LA183 for the full record.