Amateur-built MXS N21MX accident near Borrego Springs, California

Probable cause

The pilot’s inability to maintain control of the airplane following the loss of aileron and elevator control due to the forward flight control torque tube assembly’s detachment from the forward bearing. Contributing to the accident was the inadequate construction of the forward bulkhead that held the flight control torque tube assembly in place and the improper installation of the thrust bearings.

NTSB analysis

During the aerobatic practice flight, the airplane departed controlled flight. The pilot opened the canopy, which then separated from the airplane, and exited the airplane. Due to the low altitude, the pilot's parachute did not fully deploy before he impacted the ground.

The accident airplane was 1 of 14 MX-model airplanes. It was the only model built from a kit as an experimental, amateur-built aircraft, and it was constructed differently than the other MX-model airplanes. Postaccident examination of the torque tube assembly revealed that the forward bulkhead holding the torque tube assembly in place was constructed in a way that allowed the bulkhead to flex, which subsequently led the torque tube assembly to detach from the forward bearing during the accident flight and resulted in the loss of aileron and elevator control. Examination also revealed that the forward and aft bearing houses were installed opposite of the correct direction, which allowed the bearings to detach from the torque tube assembly when the front bulkhead flexed.

Text from the NTSB. Open the NTSB docket for WPR12LA407 for the full record.