ERA25LA198

The purpose of the accident flight was for the pilot and the mechanic, who was the passenger on the accident flight, to go on a short test flight after the airplane’s most recent annual inspection. The pilot reported that he performed one circuit of the airport traffic pattern, which was uneventful. During the second circuit, he decided to perform a touch-and-go landing, but the airplane bounced, so he decided to abort the landing. During the initial climb the mechanic heard a “pop,” and shortly thereafter the pilot noticed the engine speed decreased and the airplane lost partial engine power. To avoid trees, the pilot attempted to return to another runway and land, but the airplane descended and impacted a field short of the runway. Postaccident examination of the airplane revealed that the turbocharger air discharge duct had separated from the engine (this duct provided turbocharged intake air to the diesel engine). One of the two worm drive clamps that would have secured the duct to its mating hose was found separated and unsecured. The worm drive’s screw was worn and loose in the clamp housing, consistent with reuse. No evidence of any other preaccident mechanical malfunctions or failures of the engine were found during the examination. Data recovered from the engine control unit (ECU) revealed that the engine boost pressure dropped to ambient pressure during the initial climb, about the same time that the mechanic reported hearing the “pop.” Because the diesel engine relied on turbocharged intake air for power, disconnection of the turbocharger air discharge duct would have resulted in a significant loss of engine power consistent with the partial loss of engine power described by the pilot. The mechanic stated that during the airplane’s most recent annual inspection, he had removed the turbocharger air discharge ductwork, and that when he reinstalled it, he reused the worm drive clamps (rather than using new clamps as prescribed by the airplane’s maintenance manual). Given the worn and loose condition of the unsecured clamp’s worm drive found during the wreckage examination, it is likely that the reused clamp loosened during the accident flight, resulting in the turbocharger air discharge duct’s separation and the partial loss of engine power during the initial climb.

On May 7, 2025, about 1600 eastern daylight time, a Diamond Aircraft DA 40 NG airplane, N499BW, was substantially damaged when it was involved in an accident near Sanford, North Carolina. The pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, the purpose of the accident flight was to test fly the airplane after the annual inspection. He performed a preflight inspection of the airplane and found the gearbox oil level was low. He contacted the mechanic who performed the annual inspection and was told the oil level was okay for the short test flight. The pilot and the mechanic then went on the test flight together. They departed runway 21 at Raleigh Executive Jetport at Sanford-Lee County Airport (TTA), Sanford, North Carolina. The pilot reported that first circuit of the airport in the traffic pattern was uneventful. During the second circuit, the pilot decided to perform a touch-and-go landing, but during the landing the airplane bounced, so he decided to abort the landing. During the climb out, the mechanic asked if he heard a “pop,” but the pilot stated that he did not hear anything. The pilot then noticed the engine speed decrease and the airplane exhibited a partial loss of engine power. To avoid trees, the pilot attempted to return to another runway and land. He realized the airplane would not reach the runway, so he tried to land in the grass. He did not recall anything after that. According to the mechanic, he completed the annual inspection of the airplane the week before the accident flight. During the annual inspection, he removed the turbocharger air discharge ductwork to examine the rest of the engine. During reinstallation of the ductwork, he reused the worm drive clamps (that secured the ductwork to the engine) and safety wired them. The mechanic stated that the pilot approached him on the day of the accident and asked him to check the airplane’s gearbox oil level. The pilot stated it appeared to be lower than normal. The mechanic checked and found the oil plug gasket had a tear in it and he replaced the gasket with a new one. He did not remove the turbocharger air discharge duct to complete the servicing of the gearbox. He then cleaned and started the engine to check for leaks. The engine check did not reveal any anomalies, and the pilot asked the mechanic to go with him on a test flight around the airport traffic pattern. They circled around to perform a touch and go landing on runway 21; however, before landing the pilot decided to do a “go around” and leveled off the airplane above the runway. As they flew down the runway, the engine “popped” like a “backfire,” and the pilot tried to land on the remaining runway. They were going too fast and did not have enough runway length left. The pilot bounced the airplane twice and said they were going to go around. The pilot applied engine power, and the mechanic heard the enginespeed increase. Then the pilot turned the airplane left and they “fell” and impacted the ground. He did not recall anything after that. Postaccident examination of the airplane at the accident site revealed that the airplane impacted a grass field and fractured into several pieces, resulting in substantial damage. Airplane recovery personnel stated that they found the turbocharger air discharge duct under a wing beside the airplane. The airframe and engine were examined in detail after the airplane was recovered from the accident stie. The glow plugs were removed and thumb compression was obtained on all cylinders by rotating the propeller by hand. Engine powertrain continuity was established through the engine. The fuel injectors showed normal wear. The timing chain cover was removed and engine timing was verified. The turbocharger could not be rotated due to being exposed to moisture for an extended period between the time of the accident and the engine examination. The camshaft showed normal wear. The head was removed, and the pistons and valves showed normal wear. The rocker arms all showed normal wear. One worm drive clamp was separated from its normally installed location on the turbocharger air discharge duct and found under the still installed air discharge hose. The clamp was not secured/open and intact safety wire was hanging from the screw. The clamp’s screw was worn and loose in the clamp housing. The engine’s ECU was also recovered and downloaded, and the data revealed that the engine boost pressure decreased to ambient pressure consistent with the time the mechanic/passenger reported hearing a “pop” sound. The data further showed that the pilot increased the power lever to the max power position, but the boost pressure only increased to 44%. The data abruptly ended shortly thereafter. According to a representative from the airframe/engine manufacturer, separation of the air discharge duct could result in a significant loss of engine power (estimated to be 55 to 65%) due to the diesel engine not receiving full turbocharged intake air. The Diamond Aircraft maintenance manual chapter 20 provided specific torque requirements for the worm drive clamps used on Diamond airplanes. The manual also described the importance of proper clamp placement on aluminum tube beads and stressed that the engine must be cold during installation. The manual further stated that, “Worm drive clamps are for single use only. Replace clamp with a new clamp every time the clamp is loosened or removed.” The manual cautioned that improper tightening, placement, or reuse of the clamps could result in a loss of engine power.