Diamond DA 40 NG N907L

Summary

On 15 December 2023 at about 01:15 local time, a Diamond DA 40 NG registered N907L, operated by Lift Aircraft LLC, was involved in an accident near Asheville, North Carolina, United States. 2 people were on board and one was seriously injured, one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

15 December 2023 at 01:15

Classification

Accident

Location

Asheville, North Carolina, United States

Coordinates

35.4361, -82.5420

Aircraft

Diamond DA 40 NG

Registration

N907L

Category

Airplane

Year built

2023

Engines

1

Operator

Lift Aircraft LLC

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

Knoxville → Myrtle Beach

Aircraft damage

Substantial

Weather

VMC

Light

Night

NTSB number

ERA24LA066

1 person was seriously injured.

Fatigue failure of the No. 4 inner main bearing cap screw and connecting rod bolts, which resulted in a total loss of engine power. Contributing to the failure were the low material strength of the inner main bearing cap screw and the increased loads on the screw due to wear in the No. 1 fuel injector.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The airplane had a sudden, total loss of engine power in flight, which resulted in the pilots conducting a forced landing to an interstate highway. The airplane struck an energized power line before touchdown and caught fire. Metallurgical examination of the diesel engine revealed the No. 4 inner main bearing cap screw and two connecting rod bolts for either the No. 1 or No. 2 cylinder fractured due to fatigue cracking. The engine manufacturer reported a history of inner main bearing cap screw failures on the accident airplane’s engine model due to certain batches of screws that were produced at the lower end of the material strength tolerance for class 8.8 strength screws. The strength of the fractured inner main bearing cap screw was tested and found to be well below tolerance. The engine manufacturer said a lower strength screw is susceptible to failure when abnormal operating conditions are encountered, such as fuel quality issues or significant deviations from the fuel system requirements. Testing of the engine’s four fuel injectors revealed the No. 1 injector had an increased injection load, most likely due to wear resulting from corrosion or fuel contamination. According to the engine manufacturer, this increase can elevate combustion peak pressure and load on the inner main bearing cap screws. Disassembly of all four injectors revealed corrosion, contamination, and wear observed on several parts of the injectors, including armature guides, control pistons, and injector housings. A fleet-wide inspection of the operator’s aircraft, fuel trucks, and fuel farms revealed no evidence of water contamination. The operator reported that they used an engine manufacturer-approved, anti-microbial fuel additive at 25-hour intervals to prevent corrosion and contamination, since diesel engines and fuel are susceptible to water and microbial contamination. The investigation was unable to determine the source of the wear found in the fuel injectors. Fatigue failure of the connecting rod bolts in this accident appears to be an isolated occurrence; the engine manufacturer reported no previous fatigue failures of connecting rod bolts for this engine model. Examination of the fractured main bearing cap screw and connecting rod bolts did not determine which fatigue crack event occurred first. However, their fracture most likely led to the complete failure of the engine. In response to the main bearing cap screw failures, the engine manufacturer issued a mandatory service bulletin (MSB) a month after the accident for the 8.8 strength main bearing cap screws to be replaced with stronger 12.9 strength screws on this engine model. In response, the European Union Aviation Safety Agency (EASA) and the FAA issued separate airworthiness directives (ADs) that mandated the replacement of the inner main bearing cap screws to the higher strength screws. According to the engine manufacturer, there have been no further occurrences of main bearing cap screw failures since the ADs were issued.

Quoted verbatim from the NTSB record.