PIPER PA32R — Attalla, AL

What happened

While on a night cross-country flight in visual meteorological conditions, the airplane began descending, then the pilot declared an emergency and informed the controller of a loss of engine power. The controller advised the pilot of his proximity to two airports and after turning onto a westerly heading consistent with flying toward Robbins Field Airport (20A), Oneonta, Alabama, which was located about 16 nm west-southwest from the airplane’s position, the pilot realized he was closer to Northeast Alabama Regional Airport (GAD), Gadsden, Alabama, whose runways were both closed by NOTAM. The pilot twice asked about GAD, and the controller informed him both times that GAD’s longer runway was closed, and its shorter runway did not have lights. The controller also told the pilot that work was being performed on GAD’s runways, and landing there would not be feasible.

The flight continued in the general direction of 20A but was unable to reach it due to the distance, altitude, and descent rate of the airplane with reduced engine power. While maintaining controlled flight in a wings-level, slightly nose-low descent, the airplane impacted trees in mountainous terrain about 11 nm and 3.7 nm from 20A and GAD, respectively. The airplane was destroyed by a postcrash fire.

Postaccident examination of the engine revealed that one pawl retaining rivet of the left magneto impulse coupling exhibited fatigue fracture features that originated at areas of heavy wear along the shaft, followed by overload fracture. The other pawl retaining rivet also exhibited wear on the rivet shaft and subsequently fractured due to torsional and shear overstress. Deformation on the respective holes of the impulse hub assembly was noted, consistent with relative movement of the impulse hub assembly. Additional overload fractures occurred in the left magneto gear retainer assembly and multiple gear teeth of multiple gears in the accessory section of the engine, including the fuel pump idler gear assembly.

Although the airplane was equipped with an independent right magneto that was capable of operating and producing spark to one spark plug of each cylinder and an auxiliary fuel pump that was capable of providing adequate fuel to the engine in the event of an engine-driven fuel pump failure, the switch positions and operational status of these components could not be determined due to the extent of the postcrash fire. Thus, the loss of engine power was likely the result of the cascading effects from the fracturing of the left magneto gear retainer assembly and multiple gear teeth of multiple gears in the accessory section, including the fuel pump idler gear assembly.

Although both rivets and holes of the left magneto impulse hub assembly exhibited wear consistent with being loose relative to each other, the investigation could not determine when that wear or fatigue initiated, or if either was present at the last impulse coupling inspection performed about 1.5 years and 300 hours before the accident, in accordance with a non-mandatory service bulletin.

At the time the pilot declared an emergency, all construction personnel for a runway sealcoating project at GAD had left the airport, one runway was free of equipment, and both runways had operable pilot-controlled lighting. Based on the airplane’s distance flown after the pilot declared an emergency and the actual status of GAD’s runways, it is likely that the pilot could have conducted an emergency landing at GAD had he expeditiously diverted there. However, because GAD is a non-towered airport and no airport personnel were present, it would have been difficult for the controller to obtain details about the current runway conditions at GAD (beyond what the NOTAMs provided) and to relay this information to the pilot in a timely manner. Although the pilot could have exercised his authority as pilot-in-command in an emergency situation to land at GAD after being advised by the controller that its runways were closed, the information available to the pilot likely led him to proceed toward 20A instead.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.