N343WTAero Vodochody L-39ZA · 1986

On May 2, 2023, at 1610 central daylight time, an Aero Vodochody L-39Za, N343WT, was substantially damaged when it was involved in an accident near Barnhart, Texas. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot flew the airplane to San Angelo Regional Airport (SJT), San Angelo, Texas, from Ellington Airport (EFD), Houston, Texas, on May 2, 2023. The airplane was refueled on the day of the accident with 342 gallons of Jet A fuel before being hangared overnight at SJT.

The pilot reported that after taking off from SJT for a local flight, while climbing through about 7,300 ft msl, he heard a “pop” noise. He scanned the engine instruments and saw them “rolling back.” He also noted there were no caution lights illuminated. The pilot pitched the airplane for best glide and attempted a windmilling engine air start, which was unsuccessful. He then attempted a second air start using the Saphir auxiliary power unit, which was also unsuccessful. Unable to restart the engine, the pilot performed a forced landing to a dirt road in a field. The airplane’s wings were substantially damaged during the landing.

A visual inspection of the engine revealed white streaks in the engine tailpipe section. The low-pressure fuel pump was removed and disassembled. The face of the impeller blades was discolored, and a white, crusty substance was found on the inlet screen edge. The inlet screen and the impeller blades were sent to the National Transportation Safety Board (NTSB) materials laboratory for further examination. Analysis of the substance was mostly indeterminate. The examined matter had similar characteristics as cellulose (likely plant matter), soil, and several jet fuel additives including anti-corrosion products, emulsifiers, surfactants, and metal scavenging agents. Additional postaccident examinations of the airplane and engine were conducted and no anomalies with the engine or airframe were identified that would have contributed to a loss of engine power.

A fuel sample was taken from the airplane’s lower fuselage tank drain at the time it was disassembled for transport from the accident location on May 20. The sample was sent to an independent fuel testing facility for analysis. The testing measured water in the sample of 55 ppm. Recovery personnel stated that when the airplane was de-fueled during the recovery process the fuel-water separator filter, which had about ½ gallon capacity, clogged with water 3 times during transfer of 120 gallons. The recovery personnel further stated the airplane had not been rained on after the accident and before recovery.

The fixed base operator (FBO) who refueled the airplane the day before the accident conducted testing of fuel from both their Jet A fuel trucks following the accident. Testing of both samples detected water at less than 15 ppm. The maximum limit for water in fuel was listed as 30 ppm. According to the FBO, 22 aircraft had been fueled from the same fuel source before the accident and there were no reports of issues or incidents with those aircraft.

According to an NTSB National Resources Specialist (Aircraft Powerplants), recent technical literature indicates dissolved water between 60 – 100 ppm at 20°C exists in conventional petroleum-derived fuels and 50 ppm is an acceptable level. The 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. One reason for constant water accumulation in fuel during storage is the condensation of some of the water vapor when the air cools. When one cubic meter of air is cooled from 10° C to 0° C, 4.6 g of water precipitates.

Kerosene (jet fuel) absorbs the moisture hygroscopicly. When it cools, the water absorption capacity in the kerosene decreases and water precipitates out. The water does not mix with the fuel. Due to the high density, water always settles at the bottom of the container, depending on the density and viscosity.

The airplane, which had a fuel capacity of 426 gallons, had previously been refueled at EFD on March 9 and 11, 2023, totaling 296 gallons of fuel, and 77 gallons of fuel had been added at EFD on May 1, 2023.The airplane was regularly hangared at EFD and was not parked outside.