TEMECULA, CA, USA
N690JM
Aero Commander 690
The airplane collided with an airport boundary fence during an aborted landing. The pilot made a normal approach following the visual approach slope indicator (VASI) with gear down and full flaps and touched down just past the numbers and began to decelerate. The pilot selected reverse thrust with both engines. As he added power to decelerate, the airplane suddenly veered to the left and off the runway when the right engine did not go into reverse thrust. He deselected reverse thrust and aligned the airplane with the runway. He was approaching the end of the runway at high speed and elected to attempt a takeoff. The airplane went off the end of the runway onto smooth grass. The pilot rotated the airplane, but the airplane collided with an airport boundary fence and came to rest in a field. In a post accident examination, when the power levers were placed in the full reverse position, the left fuel control measured 4 degrees, while the right measured 0 degrees. The left pitch control measured 10 degrees, while the right measured 0 degrees; the controls should have read 0 degrees. A controls engineer determined that during landing, there would be a 10-degree propeller pitch control (PPC) angle mismatch, which would be about 2.5 degrees of BETA angle. With matched levers, there would be asymmetric reverse thrust with the left engine lower in torque. This would result in the airplane turning towards the left if both propellers had gone into reverse pitch.
On October 13, 2001, about 2130 Pacific daylight time, an Aero Commander 690, N690JM, collided with an airport boundary fence during takeoff from the French Valley Airport, Temecula, California. The owner was operating the airplane under the provisions of 14 CFR Part 91. The commercial pilot sustained minor injuries and the private rated copilot was not injured; the airplane sustained substantial damage. The positioning cross-country flight departed Flagstaff, Arizona, about 2030 PDT. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed. The pilot submitted a written report. He stated that he was making a visual approach to runway 18. The winds were calm, the runway lights were on, and there was no other traffic. He made a normal approach with gear down and full flaps when on final with the visual approach slope indicator (VASI). He maintained blue line plus down to short final, and came back slowly on the power as the airplane crossed the numbers at 90 to 100 knots. He touched down just past the numbers with a normal run out, and began to decelerate. During the landing roll, he selected reverse thrust (BETA) with both engines. As he slowly added power to decelerate, the left engine went into BETA, but the right engine did not. The airplane suddenly veered to the left and off the runway. He deselected reverse thrust and aligned the airplane with the runway. He was approaching the end of the runway at high speed and elected to attempt a takeoff. The airplane went off the end of the runway onto a smooth grass field. The pilot rotated the airplane, but the airplane collided with an airport boundary fence and came to rest in the field. The wings and fuselage sustained substantial damage. A technician from the engine manufacturer inspected the engines under the supervision of the Federal Aviation Administration (FAA) accident coordinator, and submitted a written report. They rotated the propellers. The left engine did not turn, but the right engine did. They observed two propeller linkages fractured on the left propeller and one linkage broken on the right propeller. All propeller blades were in the feather position. Both rpm levers in the cockpit were difficult to move. Left Engine The turbine and compressor section of the engine decoupled from the propeller. The technician noted a heavy drag when manually rotating the propeller, and the reduction gearbox was noisy. The input gearbox had two long cracks at the bottom and side of the engine inlet, but no oil leaked from the gearbox. The fuel pump's mounting flange fractured where it mated with the gearbox. The starter-generator adapter plate fractured where the starter-generator disengaged from the engine. Oil was in the oil tank on the bottom of the screen. Linkages of both the power lever and the rpm lever were connected. Right Engine The engine did not decouple from the turbine and compressor section. The propeller rotated freely, and there was no heavy drag or noise from the gearbox. Oil was in the oil tank on the bottom of the screen. Linkages of both the power lever and the rpm lever were connected, and rigging in full reverse was normal. The technician placed both power levers in the full reverse position. The left fuel control measured 4 degrees, while the right measured 0 degrees. The left pitch control measured 10 degrees, while the right measured 0 degrees. He said that the controls should have read 0 degrees. A controls engineer evaluated the rigging findings. He noted that the left engine would lag the right engine by 4 degrees in the main metering valve (MMV), and by 10 degrees in BETA. This meant that in governing mode (flight) there would be a split of 25 pounds per hour with the levers matched. The pilot would just adjust the left-hand power lever forward to match the right. During landing, there would be a 10-degree propeller pitch control (PPC) angle mismatch, which would be about 2.5 degrees of BETA angle. With matched levers, there would be asymmetric reverse thrust with the left engine lower in torque. This would result in the airplane turning towards the left. Weight flow (fuel flow) would not suffer because the fuel control unit (FCU) was on the under speed governor of the fuel control and not the power angle schedule. This explanation assumed that the rigging parallelograms were good and set correctly. The angles for the PPC and FCU were not determined for the higher angles.
a misrigging of the engine controls that resulted in an asymmetric reverse thrust condition.
Source: NTSB Aviation Accident Database
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