Amateur-built IV N37MB accident near Perry, Florida

Probable cause

A rapid throttle advancement after a period of idling, which resulted in a flooded engine and total loss of engine power.

NTSB analysis

The pilot reported a loss of engine power after descending from 11,500 ft mean sea level (msl) and leveling off under a cloud layer at 2,000 ft msl. The pilot switched fuel tanks and enrichened the mixture; however, he was unable to restore engine power and elected to execute a forced landing during which he impacted trees.

Postaccident examination of the airframe and fuel-injected engine revealed no anomalies that would have precluded normal operation. The engine subsequently started without hesitation during a test cell run at the manufacturer’s facility. After running at idle for 5 minutes, the engine was run for 5 minutes at various rpm settings. The engine test run revealed that the fuel system was mal-adjusted and set too lean, and the manifold pressure was about 2 inches of mercury lower than that required to produce rated power. This could have been due to an observed leak of the turbocharger exhaust or the sonic venturis which were open to the atmosphere for the engine test.

Following these static engine runs, the engine was brought to idle and then the throttle was rapidly advanced. When the throttle was advanced quickly, the engine ran very rich with black exhaust smoke, and then would falter. If the throttle was not immediately retarded, the engine lost power completely. If the engine was immediately brought back to idle after it faltered upon rapid throttle advancement, the engine regained power. This was consistent with the engine flooding with rapid throttle advancement after a period of idling.

Given that no anomalies were noted in the examination and that the engine repeatedly stopped producing power after rapid throttle advancement after a period of idling in the test cell, it is possible that the speed with which the pilot advanced the throttle after leveling from the descent was too quick. The engine likely then would have flooded with fuel and stopped producing power, similar to the behavior observed during the postaccident test run.

Text from the NTSB. Open the NTSB docket for ERA24LA043 for the full record.