DUPONT, LA, USA
N8648H
NORTH AMERICAN NAVION 4
THE AIRPLANE WAS SUBSTANTIALLY DAMAGED DURING A FORCED LANDING FOLLOWING A TOTAL LOSS OF ENGINE POWER. DURING THE LANDING FLARE, THE PILOT INADVERTENTLY STALLED THE AIRPLANE IN AN EFFORT TO CLEAR TREES AND WIRE. TWO 1/4 INCH 20 BY 15/16 INCH HEX SCREWS WERE FOUND LOOSE DURING THE ENGINE EXAMINATION. THESE SCREWS HOLD THE STARTER GEAR PIVOT IN PLACE. ONE OF THE SCREWS WAS OUT 1 INCH AND THE STARTER GEAR WAS FOUND MISALIGNED AND ACCESSORY GEAR TEETH WERE GRINDING. METAL WAS SHAVED FROM THE STARTER GEAR AND METAL WAS FOUND IN THE OIL SCREEN. GEAR TEETH MISSING FROM THE AFT CRANKSHAFT GEAR DISENGAGED THE CRANKSHAFT FROM THE AFT CAMSHAFT GEAR BREAKING ENGINE CONTINUITY. THE ENGINE WAS ASSEMBLED ON JULY 14, 1992. RECORDS DID NOT INDICATE THAT A MANUFACTURER SERVICE LETTER DATED SEPTEMBER 13, 1993, WHICH CONTAINED INSTRUCTIONS FOR THE HEX SCREW TIGHTENING PROCEDURES AND TAB WASHER INSTALLATION HAD BEEN ACCOMPLISHED.
On July 12, 1994, at 1010 central daylight time, a North American Navion 4, N8648H, was substantially damaged during a forced landing near Dupont, Louisiana. The commercial pilot received serious injuries. A pilot rated passenger and the other passenger received minor injuries. Visual meteorological conditions prevailed for the personal cross country flight. The pilot and pilot rated passenger stated the flight departed Baton Rouge, Louisiana, at 0930. The flight climbed to 2,500 feet MSL en route to Alexandria, Louisiana. After 25 minutes the flight descended to 1,500 feet MSL to maintain visual flight conditions. A total loss of engine power occurred and the smell of fuel filled the cockpit. The pilot initiated a descending turn at a rate of 1,000 feet per minute toward a service road. At about 75 to 100 feet above the ground, it was "obvious that the we were not going to clear the trees." The pilot leveled the wings and then "pulled back abruptly on the yoke." The airplane was "stalled completely." Witnesses and local authorities reported hearing the airplane's engine backfiring, stopping, and restarting several times, before the total loss of power occurred. The airplane was then observed making a turn toward a field and descending for a forced landing. Upon arrival at the field, witnesses reported observing a highline wire shaking and the airplane on the ground bouncing up and down. As the airplane came to rest on it's nose, witnesses and local authorities assisted the occupants. On July 26, 1994, the engine was examined (statements enclosed) at Baton Rouge, Louisiana. Two 1/4 inch 20 by 15/16 inch hex screws were loose. These screws hold the starter pivot in place. One screw was out 1 inch and the starter gear was misaligned. Metal was shaved from the starter gear and metal was found in the oil filter. Gear teeth were missing from the starter gear, crankshaft gear, and camshaft gear resulting in a loss of engine continuity. Tab locking washers were not bent against the pivot lug. Torque could not be determined. The engine was assembled on July 14, 1992. A manufacturer service letter was issued on September 13, 1993, containing instructions to discard the old washer and install a new tab washer. The starter gear pivot screws require 180 to 220 inch pounds of torque and tab (PN-501868) locking washer. Maintenance records did not indicate utilization of the service letter. The airplane was released to the owner's representative following the investigation.
THE LOSS OF ENGINE POWER DUE TO INADEQUATE MAINTENANCE ADJUSTMENT OF ACCESSORY DRIVE STARTER GEAR SCREWS WHICH DISENGAGED IN FLIGHT. FACTORS WERE THE LACK OF SUITABLE TERRAIN FOR THE FORCED LANDING AND NON COMPLIANCE WITH THE APPLICABLE SERVICE LETTER.
Source: NTSB Aviation Accident Database
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