Amateur-built XL N340XL accident near Tahlequah, Oklahoma

Probable cause

A total loss of engine power for undetermined reasons.

NTSB analysis

The pilot reported that three days before the accident flight, he had a loss of engine power and performed an uneventful forced landing into a field. The airplane was inspected by mechanics after the forced landing; however, they were unable to determine the reason for the loss of engine power. The pilot departed the field three days later. The pilot stated that one hour after departure, while cruising at 10,000 ft above ground level (AGL), the engine began to misfire. He descended to 9,500 ft AGL and tried to troubleshoot the loss of engine power and then the engine quit. During a forced landing the airplane sustained substantial damage to the wings, fuselage, and empennage.

The electronic devices removed from the airplane were either damaged and could not be functionally tested or did not reveal any pertinent data. A review of the airframe and engine logbooks did not reveal any discrepancies of uncorrected issues with the airframe or engine.

A postaccident examination of the airframe and fuel-injected engine revealed no mechanical failures or malfunctions that would have precluded normal operation. The examination did reveal that the fuel cap O-rings were cracked and slightly dry-rotted. According to the airframe manufacturer, the dry-rotted O-rings may have prevented even fuel flow from the fuel tanks due to the fuel caps being non-venting, thus requiring a tight seal for proper fuel flow. However, the pilot reported that the sump tank low fuel light never came on, and there was no evidence of blue staining on top of the wings that would have indicated improperly sealed fuel caps.

Due to impact damage, the engine could not be functionally tested and the fuel system could not be examined in its entirety. The reason for the total power loss was not determined.

Text from the NTSB. Open the NTSB docket for CEN23LA268 for the full record.