The pilot reported that, after dropping skydivers, he began a spiraling descent from 8,500 feet mean sea level (MSL) to return to the Upolu Airport (PHUP) in Hawi, Hawaii.
He reduced the Cessna 182B’s throttle to idle, added 20° of flaps, and after a few seconds, applied full carburetor heat and slowly increased the engine mixture. As the airplane descended to an altitude of about 300 feet AGL (Above Ground Level), he confirmed the mixture was full rich, the propeller was full forward, and the carburetor heat was full on.
As he increased the throttle, the engine did not respond. He completed steps to troubleshoot the loss of power, however power was not established.
He made a forced landing in a field about a mile west of the airport. The airplane encountered uneven terrain and the nose gear collapsed, resulting in substantial damage to the fuselage and engine compartment. The pilot sustained minor injuries in the crash.
A post-accident examination of the engine and fuel system revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
The gascolator contained 100LL aviation fuel and, when fuel was sumped from the airplane’s tanks, only a trace amount of water was present.
The closest official weather reporting station was at Upolu Airport, located about ¼ mile east of the accident site at an elevation of 107 feet. The airport had a non-official automated weather observing system that did not issue any long-term observations.
A weather observation recorded at Kailua/Kona Keahole Airport (PHKO), located about 34 miles south, listed the temperature of 84°F and the dew point of 71°F.
The Carburetor Ice Probability Chart in FAA Special Airworthiness Information Bulletin CE-09-35 showed a probability of serious carburetor icing at glide power, with a relative humidity of 81%.
The Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C) states: Carburetor ice is most likely to occur when temperatures are below 70° Fahrenheit or 21° Celsius and the relative humidity is above 80%. Due to the sudden cooling that takes place in the carburetor, icing can occur even in outside air temperatures as high as 100°F (38°C) and humidity as low as 50%.
Whenever the throttle is closed during flight, the engine cools rapidly and vaporization of the fuel is less complete than if the engine is warm. Also, in this condition, the engine is more susceptible to carburetor icing.
If carburetor icing conditions are suspected and closed-throttle operation anticipated, adjust the carburetor heat to the full ON position before closing the throttle and leave it on during the closed-throttle operation. The heat aids in vaporizing the fuel and helps prevent the formation of carburetor ice. Periodically, open the throttle smoothly for a few seconds to keep the engine warm, otherwise, the carburetor heater may not provide enough heat to prevent icing.
Probable Cause: The airplane’s loss of engine power due to carburetor ice that formed during a long descent, contributing to the outcome is the pilot’s delayed use of carburetor heat.
To download the final report. Click here. This will trigger a PDF download to your device.
This August 2024 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Leave a Reply