Beech 76 N6627U accident near Dunnellon, Florida

Probable cause

An inadequate 100-hour maintenance inspection that failed to detect and correct loose nuts on a single-drive dual magneto, which led to the subsequent separation of the magneto from the engine during initial climb and the total loss of engine power.

NTSB analysis

The private pilot and an examiner were conducting a practical examination flight in a multiengine airplane. The pilot stated that, after takeoff and about 100 ft above ground level, he raised the landing gear and heard a "thud"; seconds later, the airplane began an uncommanded turn to the right, consistent with a right engine failure. The examiner took control of the airplane and determined that it lacked the climb performance to clear the obstacles in its path. He then retarded the throttles and landed gear-up in the grass between the runway and hangars on the airport. During the landing, the left wing struck a concrete drain and was substantially damaged.

Examination of the airplane revealed that the right engine single-drive dual magneto had separated from the accessory pad and was laying in the engine compartment. Because both magnetos were attached to the engine at a single point, the right engine lost power completely when this event occurred. The two nuts and clamps used to attach the magneto to the mounting studs were missing; the mounting studs appeared undamaged. Given this information, it is likely that the mounting nuts loosened over time, allowing the magneto to separate from the engine. The airplane's most recent 100-hour inspection was performed about 3 weeks (27 flight hours) before the accident. A required item of that inspection was to check studs and nuts for proper torqueing and obvious defects. Had the loose mounting nuts of the magneto been detected and corrected at this time, the magneto likely would not have separated from the engine.

Text from the NTSB. Open the NTSB docket for ERA17LA077 for the full record.