Beech B36 N236BC accident near Pembroke Pines, Florida

Probable cause

The pilot’s likely activation of the auxiliary fuel pump to “high” for undetermined reasons during takeoff, which resulted in total loss of engine power due to an excessively rich fuel-to-air mixture. Also causal was the pilot’s exceedance of the airplane’s critical angle of attack while returning to the airport following the loss of engine power.

NTSB analysis

A witness heard the accident airplane during its engine run-up before takeoff and stated that the engine was sputtering and backfiring. Another witness reported that the airplane was climbing very slowly before the engine suddenly lost total power about 100 to 200 ft past the departure end of the runway at an altitude about 300 ft above the ground. The airplane entered a right bank, maintaining its pitch attitude, then “stalled” and pitched nose-down, impacting powerlines, a vehicle, and terrain; a postcrash fire ensued.

Examination of the flight controls revealed no evidence of preimpact failure or malfunction. Most of the spark plugs exhibited dark coloration consistent with a rich fuel-to-air mixture. Postaccident operational testing of the engine using only the engine-driven fuel pump revealed that, at full throttle, the engine made slightly less than its rated rpm and manifold pressure; however, the output would have been sufficient to sustain flight. During subsequent engine operational testing at full throttle with an operative engine-driven fuel pump, activation of the test cell’s fuel pump caused black smoke to emit from the exhaust and the engine to suddenly lose total power. The engine was then restarted and operated for about 5 minutes at full throttle using only the engine-driven fuel pump before being shut down. At the conclusion of the last engine run, the spark plugs exhibited normal coloration and were not dark or sooty.

While the three-position auxiliary fuel pump switch was found between the “low” and “off” positions and the position at impact could not be determined, the dark or sooty color of the spark plugs when first viewed during postaccident examination was consistent with an overly rich fuel-to-air mixture. Additionally, the witness description that the engine lost power suddenly during the takeoff was consistent with the behavior that the engine exhibited when activating an additional fuel pump during the postaccident test run.

Given this information, it is likely that the pilot turned the auxiliary fuel pump to “high,” contrary to the procedures published in the airplane’s flight manual, which resulted in an overly rich fuel-to-air ratio and subsequent total loss of engine power during the initial climb. The area of the accident site was densely populated, and it is likely that the lack of forced landing options available to the pilot contributed to the decision to turn back toward the airport at low altitude, during which the pilot exceeded the airplane’s critical angle of attack, resulting in an aerodynamic stall and loss of control.

Text from the NTSB. Open the NTSB docket for ERA21FA154 for the full record.