Ercoupe 415 C N2013H accident near Susanville, California

Probable cause

The pilot’s failure to follow the checklist while starting the engine and to lock the engine primer plunger, which resulted in the partial loss of engine power during cruise flight in highdensity altitude conditions.

NTSB analysis

The commercial pilot reported that, before the first flight leg of the day, he used the engine primer during a cold engine start. He did not use the primer before he departed for the accident flight leg. He stated that, during cruise flight, he began to slowly climb the airplane to cross a ridgeline, and, as he pushed the throttle up, the engine did not respond. He pumped the throttle numerous times, and the engine finally responded; however, the airplane had lost altitude and airspeed, and he was forced to land the airplane in a wooded area.

Examination of the wreckage revealed that the spark plugs' electrode areas were dark and sooty, indicative of a rich-mixture condition. The engine primer plunger was found in the unlocked-and-extended position, and it was undamaged and would lock when the lugs were engaged. The primer position and the condition of the spark plugs indicated that the engine power loss was likely due to an overly rich mixture, which resulted from excess fuel being pulled through the primer into the engine's intake system when power was applied.

The Starting checklist procedures indicated that, after using the primer, the primer plunger should be locked. An unsecured primer plunger can cause the engine to run richer than normal and result in a rough-running engine, loss of power, and blackened spark plugs. It is likely that, when the pilot used the primer while starting the engine before the first flight leg, he did not ensure that it was locked before initiating the accident flight in accordance with the Starting checklist and that this led to the subsequent in-flight loss of engine power. The calculated density altitude at cruise altitude at the time of the flight was about 9,240 ft, which would have further degraded the engine's performance.

Text from the NTSB. Open the NTSB docket for WPR14LA315 for the full record.