MINDEN, NV, USA
N62PJ
Fox Aircraft Corp. PEREGRINE PJ-2
THE AIRCRAFT WAS ON A DEVELOPMENTAL FLIGHT TEST PROGRAM. THE PILOT REPORTED A SPLIT FLAP SITUATION DURING THE GO-AROUND. WITNESSES OBSERVED THE AIRPLANE TURN ONTO A LEFT CROSSWIND, THEN BEGIN A RIGHT ROLL TO GROUND IMPACT. A PIN IN THE LEFT FLAP DRIVE WAS FOUND SHEARED. THE PIN WAS EXAMINED AND FOUND TO MEET THE MANUFACTURER'S MATERIAL SPECIFICATIONS. IT WAS DETERMINED THE PIN HAD FAILED DUE TO OVERLOAD SHEAR FORCES WHILE TORSIONAL AND AXIAL LOADS WERE APPLIED. THE FLAPS ARE DRIVEN BY A SINGLE ELECTRIC MOTOR WHICH ROTATES TWO INDEPENDENT FLEXIBLE DRIVE SHAFTS THAT ACTUATE THE RIGHT AND LEFT FLAP PANELS. THE SHEARED PIN BROKE THE CONTINUITY OF THE LEFT FLAP PANEL DRIVE STOPPING THE FLAP PANEL WHILE THE RIGHT FLAP PANEL WOULD CONTINUE TO EXTEND OR RETRACT. THERE WAS NO SYSTEM OR MECHANISM IN THE AIRPLANE THAT DETECTED AN ASYMMETRICAL FLAP CONDITION. TESTS OF THE FLAP SYSTEM REVEALED THE ELECTRICAL MOTOR IN THE FLAP SYSTEM WAS CAPABLE OF SHEARING THE PIN BEFORE A CIRCUIT BREAKER WOULD INTERRUPT ELECTRICAL POWER TO THE MOTOR.
On August 4, 1995, at 0926 hours Pacific daylight time, a Fox Aircraft Corp., Peregrine PJ-2, N62PJ, collided with terrain after an in-flight loss of control during a go-around from runway 34 at the Douglas County Airport, Minden, Nevada. The airplane was being operated as a developmental test flight under 14 CFR Part 91 when the accident occurred. The airplane was destroyed. The commercial pilot was fatally injured. Visual meteorological conditions prevailed at the time. The pilot reported a split flap situation by radio to his company during the go-around. Witnesses reported seeing the airplane turn left to the crosswind leg of the traffic pattern and then roll to the right. The airplane pitch attitude was observed decreasing and the airplane continued to roll until colliding with terrain. Examination of the flap system revealed a pin sheared on the left-hand drive shaft. The flaps are driven by a single electric motor which rotates two independent flexible drive shafts that actuate the right and left flap panels. Examination of system drawings and descriptions revealed that a sheared pin would break the continuity of the respective flap panel drive, stopping the flap panel while the other flap panel would continue to extend or retract. There was no system or mechanism in the airplane that detected an asymmetrical flap condition. The pin was submitted to metallurgical lab for analysis. According to the metallurgist, the pin conformed to the material specifications of the pin manufacturer and had failed due to overload shear forces on an approximate 45-degree plane. The metallurgist indicated the orientation of the direction of shear would indicate that a combination of torsional and axial loads were being applied at the time of the shear failure. The airplane manufacturer conducted tests of the flap system. The manufacturer determined the electrical motor in the flap system was capable of shearing the pin before a circuit breaker would interrupt electrical power to the flap motor.
a failure of the wing flap control system due to inadequate design, which led to an asymmetrical flap deployment during a critical flight condition and in-flight loss of control. A related factor was the lack of a split-flaps warning system.
Source: NTSB Aviation Accident Database
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