Amateur-built RANS S-6S N4427M accident near Roberts, Idaho

Probable cause

A loss of engine power due to the detachment of the left carburetor from the engine inlet manifold. Contributing to the accident was the pilot's failure to address a known engine vibration.

NTSB analysis

The pilot, who was also the airplane's owner, reported that the engine of the experimental amateur-built airplane experienced a partial loss of power while turning onto the crosswind leg of the traffic pattern after the initial takeoff climb. The pilot initiated a return to the runway, during which time the engine lost all power. The pilot unsuccessfully attempted to restart the engine and subsequently performed an off-airport landing. The airplane's right main landing gear collapsed during the landing roll, resulting in substantial damage to the airframe. Examination of the engine revealed that the left carburetor was detached from the engine inlet manifold. The impact trajectory, coupled with a lack of witness marks indicating the carburetor had struck any part of the airplane, make it most likely that the carburetor detached in flight. The owner/pilot reported that he had experienced excessive engine vibration and "kickback" during prior startups. He had considered a number of remedial measures to rectify the problem, but had not performed any of these measures prior to the accident flight. He additionally reported that he could have reduced the likelihood of the carburetor separating by more thoroughly examining the tension of its mounting hardware.

Text from the NTSB. Open the NTSB docket for WPR10LA483 for the full record.