WPR17LA050 · Diamond Aircraft IND Gmbh DA 40 NG

The pilot reported that, during cruise flight, the airframe began to shake, and he received a failure annunciation indication from both engine control units, followed by indications of an increase in oil temperature and a loss of oil pressure. He decided to perform a forced landing into a field, during which both wings impacted vegetation and the airplane sustained substantial damage. Subsequent examination revealed that a large quantity of engine oil had been expelled out of the engine breather tube and onto the belly of the airplane. Disassembly of the engine revealed heavy pitting to the piston crown and combustion chamber surfaces of the No. 1 cylinder. The damage appeared to be the result of a fatigue crack in the piston, which allowed combustion gases to create a gas path, which eventually tunneled through the piston. The path ultimately reached the lowest piston ring, allowing pressurization of the engine crankcase, resulting in the observed expulsion of oil. The crack appeared to have been initiated by a nick in the piston crown, possibly caused by ingestion of a foreign wire-like object, which was harder than the aluminum material that comprised the piston and cylinder head. A determination of the foreign object type could not be made, but there are multiple possibilities regarding the source. The induction side of the turbocharger had experienced a failure about 234 flight hours prior, and the induction-to-intake plenum was replaced 192 hours prior to the accident. A fragment of material, such as safety wire, could have been inadvertently left inside the unfiltered side of the induction system during those maintenance events and been ingested into the engine. The design of the air induction system incorporated filters for both normal and alternate air operations, and, as such, foreign object ingestion during operation was unlikely. The engine’s oil analysis history did not indicate any significant deviations throughout its service history. Such damage would likely have resulted in oil contamination; therefore, the crack likely began to propagate during the 90-hour period between the last oil analysis and the accident flight. Multiple similar piston failures have occurred to other engines in the series, seemingly initiated by either foreign object ingestion and damage or thermal overload due to an out-of-tolerance fuel injector, or a combination of both. The manufacturer released a mandatory service bulletin to address the fuel injector defects and a service letter to address the potential for foreign object ingestion following maintenance events. Although not contributing to the accident, during the investigation, a series of cracks were observed in the cylinder head of both the accident engine and a series of other similar engines. In one event, a crack led to a loss of coolant after the cooling system became over-pressurized. In all cases, the cracks had occurred before the engines had reached their service life. The FAA-certified engine was originally designed and manufactured for automobile use, and subsequently modified by the manufacturer for aviation use. As such, the engine was not operating in the manner (continuous high-power operation) for which it was originally designed. The significance of this finding could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset