Piper PA-18-150 N9858P accident near St. Augustine, Florida

Probable cause

The pilot’s failure to appropriately use carburetor heat, which resulted in a total loss of engine power due to carburetor icing.

NTSB analysis

The aerial observation pilot was mapping costal erosion; about 2 hours and 20 minutes into the flight, the engine “sputtered” three times over the course of 30 to 60 seconds before completely losing power. The pilot then began troubleshooting the loss of engine power while searching for a forced landing location. The pilot landed the airplane on a relatively sparsely populated area of the beach below. During the landing, the main landing gear dug into the sand and the airplane nosed over, resulting in substantial damage to the engine mounts, vertical stabilizer, and rudder.

Postaccident examination of the airplane’s engine revealed no evidence of any preimpact mechanical malfunctions or failures. The temperature and dewpoint conditions about the time of the accident were conducive to the formation of “serious icing at glide [idle] power.” Given the lack of any mechanical anomalies observed during the postaccident examination of the engine, it is likely that the loss of engine power was due to carburetor icing. Additionally, the pilot reported that he did not begin troubleshooting the engine anomalies until after the total power loss had occurred. Had the pilot used carburetor heat to prevent the formation of carburetor ice, or applied it immediately after the engine roughness began, the loss of engine power may have been avoided.

Text from the NTSB. Open the NTSB docket for ERA23LA066 for the full record.