Cubcrafters Inc CC11-160 N232LT accident near San Luis Obispo, California

Probable cause

The pilot's inadequate instrument scan during cruise flight, which resulted in his failure to notice a loss of engine oil pressure. Contributing to the accident was the failure of the oil pressure transducer supply line, which resulted in oil exhaustion and a total loss of engine power.

NTSB analysis

The pilot reported that, about 40 minutes after takeoff for the local sightseeing flight, he noticed that the engine oil gauge wasn't indicating properly and that, about 1 minute later, the engine started to "skip." Shortly later, the engine lost all power, and the pilot performed a forced landing to a field. The experimental light-sport airplane nosed over and sustained substantial damage. Neither occupant was injured.

Examination revealed considerable oil streaking along the airplane's entire belly in an area obscured from the pilot's view while in flight. Further examination revealed that the oil pressure transducer supply line, which was made of copper tubing, had separated from its fitting on the engine accessory case. Data from the airplane's engine monitoring system (EMS) showed that, about 9 minutes after takeoff, the engine oil pressure dropped out of range, indicating that the supply line failed at that time; the data also showed that a flashing visual oil pressure alert occurred. For the remaining 28 minutes of flight, the oil pressure remained the same, and the alert remained active as all of the engine's oil was expelled out of the separated oil pressure transducer supply line and overboard.

The failed copper tubing oil pressure transducer supply line was the subject of a service bulletin (SB), which recommended either periodic inspection of the copper tubing for leaks or replacement of it with a flexible hose. Despite being inspected in accordance with the SB, the supply line still failed. Following the accident, the airplane manufacturer issued a mandatory service alert, which required the replacement of the copper tubing with a flexible hose.

As noted, the EMS data indicated that a flashing visual oil pressure alert was issued to the pilot as soon as the oil pressure transducer supply line failed; however, he did not notice the alert and continued the flight. He eventually observed the alert just before the engine seized. If he had noticed when the supply line failed, he would have had ample time to return to the departure airport before the oil was exhausted. Given that this was a sightseeing flight and that the majority of it was flown toward the sun, it is likely that the pilot was distracted during the flight and possibly encountered sun glare that obscured a clear view of the airplane's instrument panel.

Text from the NTSB. Open the NTSB docket for WPR15LA085 for the full record.