Aero Vodochody L39 N139RT accident near Oneida, Tennessee

Probable cause

The pilot's failure to maintain airplane control following a partial loss of engine power during initial climb. The reason for the partial loss of engine power could not be determined due to extensive postimpact damage.

NTSB analysis

The pilot of the single-engine, high-performance, jet airplane was scheduled to be the final performer at an air show. Several witnesses who observed the airplane take off reported that the airplane seemed "slow" during climbout. A witness located near the end of the departure runway stated that the airplane did not appear to be climbing as quickly as other jet-powered airplanes he had previously observed. This witness reported that the airplane made a right turn and pitched -up to gain altitude, and then the engine lost power. The airplane subsequently descended nose first and impacted trees and terrain about 2 miles west of the airport. The wreckage was severely fragmented, scattered along a 325-ft debris path, and partially consumed by a postimpact fire.

Examination of the airframe and engine did not reveal evidence of any preimpact mechanical malfunctions. Although bending of fan blades opposite the direction of rotation indicated that the engine was rotating at the time of impact, imprints of fan blade tips on the shrouds with no circumferential rub marks indicated that the engine had little rotational energy and was operating at low power. Extensive damage to the fuel control unit precluded a functional test for any anomalies that could have resulted in or contributed to a loss of engine power.

Although one toxicology laboratory identified ethanol in the pilot's muscle tissue, a second laboratory did not, indicating that the ethanol was from postmortem production and did not play a role in the accident. In addition, metoprolol and diphenhydramine were identified in the pilot's muscle and brain tissue. Metoprolol, a medication for hypertension, is not impairing. Diphenhydramine is a significantly impairing sedating antihistamine; however, without a blood level, no determination could be made as to whether the pilot was impaired by the effects of diphenhydramine at the time of the accident.

Text from the NTSB. Open the NTSB docket for ERA15FA353 for the full record.