Piper PA18 N5907Y accident near Delta Junction, Alaska

Probable cause

The total loss of engine power due to carburetor icing, which resulted from the pilot's failure to use carburetor heat while operating at low power settings in conditions conducive to the formation of carburetor ice.

NTSB analysis

According to the pilot, while maneuvering the airplane in mountainous terrain, he reduced engine power and initiated a descent; the engine then began to cough and run roughly. He applied full throttle, and the engine subsequently lost total power. In an attempt to restore power, he applied carburetor heat and switched fuel tanks while initiating an emergency descent. The engine restarted; however, it continued to run roughly and would not develop full power. He continued the emergency descent and landed the airplane on a mountain ridge. Upon touchdown, the left main landing gear separated from the fuselage and the left wing struck the ground, which resulted in substantial damage to the left wing.

A postaccident examination of the engine, which included an engine test run, revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

According to a carburetor icing probability chart, an airplane operating in the ambient conditions at the accident site could expect carburetor icing while at cruise power and at glide power. It is likely that, when the pilot reduced engine power for the descent, carburetor ice formed and resulted in the loss of engine power.

Text from the NTSB. Open the NTSB docket for ANC18LA080 for the full record.