What happened
During the initial climb phase, a twin-engine airplane entered a steep right bank and transitioned into a spin at an altitude of less than 700 feet. The aircraft subsequently descended and struck the ground approximately 1.5 miles from the departure runway's end. Observers near the site reported hearing abnormal engine noises immediately preceding the aircraft's loss of control. At the time of the accident, weather conditions were characterized by daylight and visual meteorological clarity.
Findings
An investigation into the right engine revealed that the ring gear support within the engine/propelle gearbox had suffered a fracture. This failure was attributed to high cycle fatigue originating from the corner radii of the high-speed pinion cutout, though the specific cause of the fatigue remains undetermined. This structural failure caused the ring gear support to disengage from the ring gear, which interrupted the transfer of power from the engine's power section to the propeller.
While the Honeywell TPE-331 engine is equipped with a Negative Torque Sensing (NTS) system designed to manage engine failures by reducing drag, this system became inoperable due to the drive train disconnect. Following the failure, a pilot action to reduce power caused the propeller governor to sense an underspeed condition. This triggered the governor to attempt to increase engine RPM by unloading the propeller, which inadvertently drove the propeller out of the feathered position toward the low pitch stop. The resulting increase in aerodynamic drag from the unfeathered propeller created significant asymmetric yawing, leading to the loss of control.