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Engine Failure During Cruise Leads to Emergency Landing; Carburetor Heat Box Improperly Rigged (N7662X)

Unionville, IA, US

On February 25, 1989, a Cessna 172B (registration N7662X) was involved in an aviation accident near Unionville, IA. Investigators recorded the probable cause as: THE FAILURE OF THE ENGINE DUE TO CARBURETOR ICE. CONTRIBUTING FACTORS INCLUDED CARBURETOR ICING CONDITIONS, IMPROPER USE OF THE CARBURETOR HEAT CONTROL BY THE PILOT, AND THE IMPROPERLY RIGGED CARBURETOR AIR BOX WHICH RESULTED IN REDUCED CARBURETOR HEATING… This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-07-04Data APIEditorial standards

While cruising, the engine quit. Emergency procedures failed, and an emergency landing was attempted on a snow-covered field. Collision with a ditch tore off the nose gear; the aircraft slid 300 feet and came to rest on its nose. Investigation found carburetor heat box misrigged and a missing seal.

Event Description

According to the pilot, while cruising to the destination airport, the engine experienced a sudden loss of power. The pilot performed emergency procedures, but these did not restore engine power. Consequently, the pilot attempted an emergency landing on a snow-covered farm field. During the landing roll, the aircraft collided with a ditch, which tore off the nose gear. The aircraft then slid for approximately 300 feet before coming to rest on its nose.

Investigation Findings

The post-accident investigation revealed that the carburetor heat box was improperly rigged. Additionally, a seal was missing from the flapper valve within the carburetor heat system. According to icing probability charts, the meteorological conditions at the time of the accident were conducive to carburetor icing. The misrigging of the carburetor heat box prevented the full application of carburetor heat. After the engine quit, the pilot attempted to restore power by applying carburetor heat, but was unable to do so due to the misrigging.

Engine failureIcing

Frequently asked questions

What happened in the 25 Feb 1989 Cessna 172B accident near Unionville, IA?

While cruising, the engine quit. Emergency procedures failed, and an emergency landing was attempted on a snow-covered field. Collision with a ditch tore off the nose gear; the aircraft slid 300 feet and came to rest on its nose. Investigation found carburetor heat box misrigged and a missing seal.

What aircraft was involved and where did it happen?

The accident on 25 Feb 1989 involved a Cessna 172B, registration N7662X, at Unionville, IA.

What was the probable cause of the accident?

THE FAILURE OF THE ENGINE DUE TO CARBURETOR ICE. CONTRIBUTING FACTORS INCLUDED CARBURETOR ICING CONDITIONS, IMPROPER USE OF THE CARBURETOR HEAT CONTROL BY THE PILOT, AND THE IMPROPERLY RIGGED CARBURETOR AIR BOX WHICH RESULTED IN REDUCED CARBURETOR HEATING CAPABILITY.

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001213X27784. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.