Aeronca 7AC N83547

The student pilot and flight instructor were practicing takeoffs and landings on grass next to a runway. The pilot reported that, on the downwind leg of the traffic pattern, the instructor directed the student to demonstrate a simulated engine failure, followed by a go-around. When the airplane was about one-quarter of the way down the parallel runway, he told the student to go around. Shortly later, the engine “sputtered” and then lost all power. While attempting to maneuver the airplane during the subsequent forced landing attempt, the airplane struck a hanger. The airplane was substantially damaged, and the student and instructor sustained minor injuries. Following the accident, the student reported that, when he attempted to put the carburetor heat back in, it was possible that he inadvertently closed the fuel shutoff valve. Postaccident examination and a test run of the engine revealed no evidence of any preaccident mechanical failures or malfunctions that would have precluded normal operation. Given this information, it is likely that the loss of engine power was the result of the student pilot’s inadvertent actuation of the fuel shutoff valve instead of the carburetor heat. Postaccident examination of the airplane further revealed that the fuel shutoff valve assembly was missing a grommet. When installed, the grommet provided support to the fuel shutoff rod and resistance to motion. Additionally, the aperture in which the grommet was typically installed was elongated. Examination of the universal joints attached to the fuel shutoff lever and valve revealed that they were worn and moved easily. All these factors resulted in the fuel shutoff lever being allowed to move easily. The airplane’s most recent annual inspection was completed about 3 months before the accident, during which maintenance personnel should have noted the discrepancies with the fuel shutoff system. Additionally, the airplane was not equipped with an optional fuel shutoff valve guard. Had these discrepancies been rectified, and had the optional guard been installed, it is possible that the student pilot might not have inadvertently activated the fuel shutoff valve. The airplane had originally only been equipped with lap belts; however, shoulder harnesses were found installed on both the front and rear seats. The investigation could not determine who manufactured the shoulder harness assembly because it resembled many previously and currently manufactured aftermarket shoulder harness assemblies, and it had no part or serial numbers on it. Review of the airplane’s maintenance records did not reveal when or by whom the shoulder harness assemblies had been installed on the airplane. During the impact sequence, the rear seat shoulder harness assembly pulled loose from its mounting location. Examination of the rear seat shoulder harness assembly revealed that it was not bolted, fastened, or positively secured to the airplane’s tubular structure but was instead clamped over two, 5/8-inch-diameter tubes with upper and lower triangular attachment brackets just forward of where the tubes intersected with the top longeron. Examination of the attachment brackets revealed that, during the impact sequence, the bracket assembly likely either mechanically pulled or slid over the airplane’s structural tubing. It was noted that the back seat occupant was more seriously injured than the front seat occupant, whose shoulder harness did not separate from the structure. On the basis of this evidence, it is likely that the detachment of the rear shoulder harness assembly contributed to the instructor’s injuries because it allowed him to strike the front seatback and his control stick.

Quoted verbatim from the NTSB record.