Amateur-built Coot N69BD accident near Deer Park, Washington

Probable cause

The pilot's failure to maintain sufficient airspeed and his exceedance of the airplane's critical angle of attack, which resulted in an aerodynamic stall and subsequent spin. Contributing to the accident was the pilot's diverted attention due to the rough running engine, which resulted from a rich fuel/air mixture, and the pilot's decision to conduct the flight in the airplane in which he had little experience flying despite knowing the airplane had preexisting engine problems.

NTSB analysis

The private pilot departed in the experimental amateur-built airplane for the local flight during daytime visual meteorological conditions. A pilot reported that he had spoken to the accident pilot before the accident and that he had told him that he had been having problems priming the carburetor because the accident airplane's fuel tanks were below the engine. The accident pilot further told him that he had installed an electric boost pump to prime the carburetor and hoped that the engine-driven fuel pump would maintain engine operation. The accident pilot added that, during engine ground runs with the electric boost pump on, the engine was running too "rich" and "rough" and that he planned to turn the electric boost pump off to see if it would work. The pilot assumed that the accident pilot intended to do this on the ground, but it was unclear.

One witness, who was a rated pilot, reported that, after takeoff and while the airplane was upwind, he heard the engine "sputtering." The airplane then turned left and remained within the airport traffic pattern. Another witness, who was in an airplane in the airport traffic pattern, reported that he observed the accident airplane "enter a spin" and descend toward the ground "on the base leg near final." No distress calls were heard on the airport's common traffic advisory frequency.

Wreckage and impact signatures were consistent with an upright spin impact with terrain. Postaccident examination of the airplane and engine revealed that the upper spark plugs exhibited signatures consistent with a rich fuel/air mixture. No additional evidence of any preexisting anomalies that would have precluded normal operation were observed. Based on the available evidence, it could not be determined if the pilot had the electric fuel boost pump turned on during takeoff or at any time during the flight.

Review of the pilot's personal logbooks revealed that, over the past 38 years, he had only accumulated 71 hours of flight time, 5.3 hours of which were in the 90 days before the accident. In addition, no record of any flight time in the accident make/model airplane was found. Given the evidence, it is likely that the engine was running roughly and that this diverted the pilot's attention and led to his failure to maintain adequate airspeed and to exceed the airplane's critical angle of attack, which resulted in an aerodynamic stall and subsequent spin while maneuvering from the base leg to final. Given the known preexisting engine problems, the pilot should not have conducted the flight in the airplane in which he had little experience flying.

Text from the NTSB. Open the NTSB docket for WPR16FA001 for the full record.