Amateur-built LSA N1908A accident near Kalispell, Montana

Probable cause

An excessive pitch control input for undetermined reasons while the airplane was operating above maneuvering speed, which led to a structural failure of the right wing during cruise flight. Contributing to the accident was the poor construction quality of the airplane and the inadvertent omission by the pilot/builder of a series of structural airframe components.

NTSB analysis

The experimental amateur-built airplane was flying in trail behind a group of two other airplanes. The takeoff appeared to be uneventful and the weather unremarkable. Automatic dependent surveillance-broadcast (ADS-B) data indicated that, after climbing to about 1,850 ft above ground level (agl), the airplane leveled off and accelerated to cruise speed. About 1 minute later, the airplane appeared to aggressively pitch down, then up, then down again before the right wing separated from the airplane and the airplane descended to impact the terrain.

Damage signatures indicated that the right wing initially folded downwards almost 90° before breaking away in an upwards direction, likely as the airplane rolled to the right.

The pilot built the airplane from plans, and its primary fuselage structure was made of tubular steel covered in fabric. He used an unapproved welding process to construct the airframe and used thicker walled tubing to compensate. Postaccident examination of the wreckage showed the weld quality was generally poor, and a set of structural bracing components in the main wing spar carry-through section was omitted. Even with the poor build quality, the steel airframe structure appeared to be intact before impact. The omission of the braces alone would not have resulted in the failure of the wing as observed: however, the combined effect of the omission and modifications would have affected the overall structural integrity of the airplane.

ADS-B data showed the airplane was traveling below the never exceed speed (Vne), but well over maneuvering speed (Va) at the time of the breakup; therefore, an aggressive control input would likely have resulted in structural damage. A negative failure of the right wing, as observed, could have been caused by a nose-down control input, and the ADS-B data indicated that the airplane had aggressively pitched down just before the breakup. The resolution of the ADS-B data did not allow for an accurate assessment of the g-forces encountered during the final oscillations.

The airplane was equipped with dual controls including a center stick. The passenger, who was seated in the rear of the airplane had not flown with the pilot in the airplane before. The passenger’s seatbelt was not buckled when examined, and although it had sustained damage it still appeared to operate. The damage observed did not explain why it was unbuckled. If the passenger was unrestrained, inadvertent flight control operation could not be ruled out. Additionally, although friends stated that it was not in the pilot’s nature to take risks, his performance of an ostentatious maneuver just before the breakup could not be ruled out.

Text from the NTSB. Open the NTSB docket for WPR22FA169 for the full record.