NTSB Identification: ANC11FA093
14 CFR Part 91: General Aviation
Accident occurred Sunday, September 04, 2011 in McGrath, AK
Probable Cause Approval Date: 12/19/2012
Aircraft: PIPER PA-18-150, registration: N13973
Injuries: 1 Serious.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The airplane was on short final approach to the airport when its engine would not respond to throttle input. The airplane descended into trees and impacted terrain. The pilot reported that immediately prior to the loss of engine power, he had made an elevator trim control adjustment and was in the process of making a throttle adjustment when he heard a snap and the engine quit operating, "as if the magnetos had been shut off." Examination of the airplane established that the throttle cable was intact. The engine was run, and no anomalies were noted. During the engine run, the magneto switches were turned off while the engine was at cruise rpm. The switches made an audible click/snap when turned off. Following a similar August 29, 2011, accident also involving a Piper PA-18 airplane, the pilot reported that, during the initial climb, he inadvertently switched off the engine magnetos with his coat sleeve while using the trim handle, causing the airplaneā€™s engine to shut down. As with this accident airplane, the magneto switches were located on the left side of the cabin, just above the trim handle. As a result of incidents involving the inadvertent shutting off of the magneto switches, the Federal Aviation Administration published a notice of proposed rulemaking announcing its intent to issue an airworthiness directive requiring the reconfiguration of the magneto switches on Piper PA-18 airplanes. Given the absence of any mechanical issues with the airplane, as well as the location of the magneto switches and the trim handle, it is likely the pilot inadvertently shut off the magnetos switches while trimming the airplane on short final approach.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot inadvertently switched off the engine magnetos during short final approach, which resulted in a loss of engine power. Contributing to the accident was the manufacturer's placement of the magneto switches in the cabin.

Full narrative available

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