Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Confusion; Distraction; Time Pressure
Aircraft Equipment Problem Critical
Preliminary information: The aircraft is a BE-9L with a 'Power 90' engine conversion STC. The engines are Walter M601 E-11s with Avia five bladed props. The preflight; start and taxi were all normal. During takeoff after rotation and initial climb with about 100 feet of altitude; gear retraction was initiated and bleed valves closed. As the right bleed valve was closed there was an audible sound of power loss and rapid yaw of the nose to the right. I returned my right hand to the yoke and applied rudder and aileron to maintain aircraft control as I simultaneously lowered the nose to maintain airspeed of 105 KIAS. I identified the loss of power; verified it and feathered the right propeller. Aircraft control was maintained straight ahead and the call made to Tower that I had an engine out and was returning to the field to land. Maintaining single engine climb speed; I was able to establish a shallow climb and a half standard rate turn into the good engine with left rudder trim applied and takeoff power still set on the left engine. At this point I finished securing the right engine. After communicating my intentions to land at the departure airport; I aligned with the centerline of the runway configured appropriately for a single engine landing. The landing was normal; braking was normal. I taxied the aircraft clear of the runway shut the left engine down and arranged to tow the aircraft to parking.Investigation by Maintenance determined that part of the throttle linkage of the right engine was inadvertently lubricated and made it possible for the throttle to 'snap' backward under normal takeoff conditions. This happened during the time after I had moved my hand from the throttles and right when I was setting the right bleed switch closed. The snapping back action of the right throttle was duplicated during full power run-ups and recorded by Maintenance. The gradual unexpected loss of power by throttle movement creeping aft is something I have seen throughout the years. This was not what happened. The throttle 'snapped back' in probably less than half a second. Compounding the situation was that with this engine STC the throttle travel from full power to idle is just a little less than a full knob width. I did not notice the aft travel of the right engine's throttle as I was leaning over the power quadrant to retract the gear and turn the bleed valves to close. My assumption was that the right engine had failed based on the rapid loss of thrust and yawing and audible power loss. As that would be the worst case I applied my training for the perceived situation. However; in doing so I inadvertently feathered and secured the right engine because of an unexpected uncommanded throttle movement. Maintenance will replace the parts of the linkage that were inappropriately lubricated. This should give normal throttle operation back to the right engine. The most difficult part of this situation was the requirement for quick decision-making and performance when an unexpected occurrence takes place in a critical phase of flight. The actions I took was a reversion to training. It put the aircraft in a position that I knew it would fly in. Unfortunately; that action was inappropriate. That action was performed well; but was unnecessary. This occurrence highlights for me that planning for every situation is impossible and that defaulting to what will work when time for troubleshooting is limited is useful.
A BE-9L 'Power 90' engine was shutdown and the flight returned to land after the throttle 'snapped' backward during takeoff. Maintenance discovered an incorrect part of BE-9L right engine throttle linkage was lubricated.