What happened
During a maintenance test flight, a Cessna 441 experienced a significant loss of directional control during its takeoff roll. The pilot reported an over-torque condition in the right engine, which led to the aircraft veering left and departing the runway. Although the pilot attempted to abort the takeoff by retarding both power levers and placing the propellers in reverse, the aircraft continued to drift. The aircraft eventually pitched up before crashing on its nose and left wing, coming to rest in an upright position. A fire broke out following the impact, resulting in the total destruction of the airframe.
At the time of the abort, approximately 6,000 feet of runway remained. A passenger and mechanic on board, who was monitoring engine gauges, noted that he did not see any over-torque indications on the instruments before noticing the aircraft drifting. The pilot, focused on the engine instruments, also realized the deviation only after the aircraft had already begun to move off the runway.
Findings
Investigation into the engine behavior highlighted potential issues documented in the Cessna Service Newsletter SLN99-15 and AlliedSignal Operating Information Letter OI 331-17. These documents describe an abnormality where an uncommanded increase or fluctuation in engine fuel flow can occur, leading to unexpected high torque and asymmetric thrust. This specific condition is linked to an open torque motor circuit within the engine fuel control.
While the Cessna 441 Flight Manual states the aircraft remains controllable with one engine inoperative at 91 knots, a specific electronic engine control failure can create an extreme torque differential. If one engine accelerates to the fuel flow stop limit while the other engine is retarded to idle, a torque differential of approximately 2,288 ft-lbs can occur. This uncommanded engine acceleration to maximum power creates a thrust imbalance so severe that the aircraft becomes uncontrollable.