Amateur-built Wheeler Express CT N246TM accident near Madras, Oregon

Probable cause

The pilot's failure to maintain adequate airspeed while maneuvering in the airport traffic pattern for landing, which resulted in an exceedance of the airplane's critical angle of attack, a subsequent aerodynamic stall at an altitude too low to recover.

NTSB analysis

The private pilot, who was the builder of the experimental, amateur-built airplane, was approaching the airport for landing on a 3-mile left base leg at the conclusion of a cross-country flight. Shortly after being cleared for landing, witnesses observed the airplane make a steep left turn and dive toward the terrain.

Ground scar analysis and wreckage fragmentation revealed that the airplane collided with terrain in a near-vertical, nose-low attitude; the wreckage was consumed by a postcrash fire. Examination revealed no mechanical malfunctions or anomalies that would have precluded normal operation of the airplane or engine, although a thorough examination of the flight control system could not be completed due to the extent of the thermal damage.

The airplane was equipped with a 'cruciform' (mid-mounted horizontal stabilizer) tail. Several years before the pilot completed the airplane, the kit manufacturer disseminated a report to owners regarding the design and aerodynamic characteristics of the cruciform tail. It stated that the airplane's tail "may stall on approach and turbulent conditions or upon crossing another airplane's wake (or its own wake in a turn)" and that "rapid action must be taken to avoid diving straight into the ground." A report partially sponsored by the Federal Aviation Administration detailing the airplane's aerodynamic characteristics stated that, "during post stall and high yaw maneuvering the horizontal/elevators seemed to have inadequate effect" which "seemed to be caused by blanking of the horizontal tail and elevators by the vertical stabilizer at the highly yawed condition."

Given these reported characteristics and the lack of mechanical anomalies found, it is likely that the pilot exceeded the airplane's critical angle of attack while turning from the base leg to final approach and the airplane entered an aerodynamic stall; the pilot was unable to recover from the near-vertical descent at low altitude.

Text from the NTSB. Open the NTSB docket for WPR17FA185 for the full record.