Schweizer 269C-1 N9421K accident near Naples, Florida

Probable cause

A loss of engine power due to the improper installation of the right magneto by maintenance personnel resulting in subsequent loss of engine power. Contributing to the accident was the inadequate 100-Hour inspection by the mechanic when he failed to note that improper hardware were installed at both magnetos, and his failure to detect fracture of the clamping flange of the right magneto.

NTSB analysis

The 19-hour helicopter student pilot departed on a cross county flight and shortly after takeoff the helicopter experienced a loss of engine power. While attempting to return, the pilot allowed the main rotor rpm to decay and while descending, the helicopter contacted a building, trellis, and then the ground. Inspection of the helicopter revealed no evidence of preimpact failure or malfunction of the flight controls, main rotor or tail rotor drive systems. The engine was removed from the helicopter and test run after proper timing of the right magneto; no discrepancies were noted. The engine had been overhauled approximately 124 hours earlier; overhauled magnetos were installed at that time. The engine had been inspected three times since the overhauled engine was installed; the last 100-Hour inspection was approximately 29 hours earlier. The mechanic who performed the last 100-Hour inspection reported using the engine manufacturer's inspection guide and 14 CFR Part 43 Appendix D as references. He did not check the magneto breaker points for pitting and minimum gap as specified in the engine manufacturer's 100-Hour inspection guide. Appendix D specified that the engine accessories are to be checked for apparent defects in security of mounting. There was no record that the magnetos had been removed since the overhauled engine was installed. The cause of the loss of engine power was determined to be caused by rotation (advance) of the right magneto which was due to an incorrect gasket and also by undetected fracture of the clamping flange. While there was no discrepancy with the left magneto, it also had an incorrect gasket installed.

Text from the NTSB. Open the NTSB docket for ERA09FA355 for the full record.