Cessna 172 N8337X accident near Manassas, Virginia

Probable cause

The pilot’s failure to apply carburetor heat before reducing engine power during a prolonged descent while operating in environmental conditions conducive to the development of carburetor ice, which resulted in a total loss of engine power due to carburetor icing.

NTSB analysis

The pilot reported that the airplane was in cruise flight at 5,500 ft mean sea level (msl) before he reduced engine power to comply with air traffic control descent instructions. The pilot did not apply carburetor heat at any time during the descent from 5,500 ft to 2,000 ft. At 2,000 ft msl, with the destination airport in sight, he applied throttle, but the engine did not respond. The pilot informed the tower controller that the “motor was unresponsive” and was cleared to land. The airplane touched down in a grassy area on airport property short of the runway, collided with a drainage culvert, and nosed over, resulting in substantial damage to the vertical stabilizer and the right-wing lift strut.

Although low compression was noted in two cylinders during the postaccident engine examination, that condition was attributed to leakage past the intake valves and likely would not have resulted in the total loss of engine power reported by the pilot. Review of weather information indicated that the airplane was operating in an area conducive to the development of serious carburetor ice at glide or idle engine power settings. It is likely that the carburetor accumulated ice during the prolonged descent without the use of carburetor heat, which resulted in the total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA24LA178 for the full record.