Amateur-built S12XL N449JP accident near Port Isabel, Texas

Probable cause

An exceedance of the airplane’s critical angle of attack and aerodynamic stall following a loss of engine power during an unknown phase of flight, which resulted in an impact with terrain.

NTSB analysis

The noncertificated pilot and flight instructor departed on an instructional flight in the experimental airplane. The airplane was later located about 1/3 mile south of the departure airport. There were no witnesses to the accident. The airplane sustained substantial damage to the wings and fuselage.

A postaccident examination of the airplane revealed that engine exhibited detonation and scoring of its cylinders, which would have resulted in a loss of engine power. Incorrect timing, poor fuel quality, and lubrication breakdown could have contributed, however, based on the available evidence, the reason for the detonation could not be determined.

The impact damage of the airplane and lack of ground scarring was characteristic of a low-speed nose-down impact with terrain, which would have resulted from an aerodynamic stall. The airplane make and model is categorized as rapidly losing energy (airspeed/altitude) when there is a loss or reduction of engine power. The airplane was equipped with a snow mobile engine. The required airplane flight testing was not performed following the installation of the engine and, as a result, may have induced negative handling qualities during low-speed flight, such as those near the stall flight regime.

Although the flight instructor’s autopsy showed signs of heart disease it’s unlikely this impaired his ability to respond to the engine failure. Additionally, the noncertificated pilot’s autopsy showed cardiovascular disease that increased his risk of experiencing a sudden impairing or incapacitating medical event. Toxicology testing detected Duloxetine; a medication commonly used to treat depression. Metaxalone, cetirizine, and Chlorthalidone were also detected and combined had the potential to cause impairment. However, because the flight instructor was the only qualified pilot abord the airplane, held the responsibility for ensuring the safe operation of the flight, and for responding to the engine emergency, the noncertificated pilot would have not had the skill or experience to play more than a very limited role. Thus, it is unlikely that the effects of his medical conditions or medications contributed to the accident.

Text from the NTSB. Open the NTSB docket for CEN21LA088 for the full record.