What happened
The pilot was operating an aircraft as the third plane in the traffic pattern, preparing to land on runway 17. During the downwind leg, the pilot applied carburetor heat as a precautionary measure. Engine power was maintained until the aircraft reached a position three miles from the airport on final approach. At that point, the pilot reduced power and established a glide path.
Shortly after establishing the glide, the pilot advanced the throttle to adjust the descent rate. However, the engine failed to respond, remaining stuck at idle power despite further throttle input. The aircraft was unable to regain sufficient thrust for a safe landing configuration based on the reported sequence of events.
The investigation
Examination of the circumstances surrounding the incident focused heavily on environmental conditions and mechanical functionality. Weather data from an airport located 10 miles north of the accident site indicated a temperature of 55 degrees Fahrenheit and a dew point of 29 degrees Fahrenheit. These conditions are conducive to carburetor icing, even when ambient temperatures are relatively high.
Following the incident, the aircraft underwent a complete rebuild. Upon completion of this project on January 14, 1989, the engine was run for operational testing. The engine operated normally during this test, and no mechanical defects were identified that could explain the loss of power. This suggests the issue was transient and likely related to environmental factors rather than a persistent mechanical failure.
Findings
The primary factor contributing to the event was the inability of the engine to accelerate above idle power during a critical phase of flight. The combination of reduced power settings for gliding and specific atmospheric conditions created a high risk for carburetor icing. Although carburetor heat had been applied earlier in the pattern, it is possible that ice accumulated or persisted in a manner that affected engine performance later in the approach.
The lack of mechanical faults found during post-incident testing supports the conclusion that the power loss was not due to equipment failure. The weather data provides strong evidence that icing conditions were present and likely played a significant role in the incident.