Flight Design CTLS N121YT accident near Greenville, South Carolina

Probable cause

A total loss of engine power resulting from the in-flight disconnection of oil hoses from the oil thermostat.

NTSB analysis

The pilot was nearing his destination airport on the first flight after a condition inspection was completed when the engine oil pressure dropped to zero. He declared an emergency and attempted to divert to a closer airport; however, after about 4-5 minutes the engine lost power. Once he realized he would not be able to glide to an airport, the pilot deployed the ballistic parachute system at about 500 ft above ground level. The airplane descended into trees, resulting in substantial damage to the fuselage and left wing.

A postaccident examination of the engine found the hoses from the oil tank to the thermostat and from the thermostat to the oil cooler had disconnected. The examination also found that the No. 3 connecting rod bearing displayed failure signatures consistent with a lack of lubrication. The valvetrain components in the cylinder head and the cylinder bores were dry due to a lack of lubrication. Based on this information, it is likely that the disconnection of the oil lines from the thermostat prevented oil from reaching critical components within the engine and subsequently resulted in the failure of the No. 3 connecting rod bearing.

A review of maintenance records showed that the airplane’s annual condition inspection was completed two days before the accident flight. The review also found that the oil system hoses had been replaced a year prior as required by the engine manufacturer, and that the airframe had accumulated 152 flight hours since the hoses were replaced. The mechanic who performed the annual condition inspection reported that he did not remove any hoses from the thermostat. The mechanic reported checking the hoses for security, and that they did not come off when tugged on. The investigation was unable to determine why the oil hoses became disconnected from the oil thermostat in flight.

Text from the NTSB. Open the NTSB docket for ERA22LA011 for the full record.