NTSB Identification: SEA01LA063.
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Accident occurred Thursday, March 08, 2001 in Saint Helens, OR
Probable Cause Approval Date: 07/30/2001
Aircraft: Piper PA-24, registration: N6337P
Injuries: 2 Uninjured.

NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

While en route in conditions conducive to carburetor icing, the pilot noticed a reduction in the aircraft's exhaust gas temperature (EGT). Although he leaned the fuel mixture, this did not seem to increase the EGT to where he thought it should be. He therefore momentarily applied the carburetor heat and checked for a decrease in engine rpm, as is the proper procedure in an aircraft equipped with a fixed-pitch propeller. But since this aircraft was equipped with a constant-speed propeller, he should have checked for a drop in manifold pressure, which he did not do. Soon thereafter, the engine lost all power and the pilot descended to a forced landing in a soft wet field. Although the intentional gear-up touch-down was uneventful, as the aircraft slid across the field, it encountered a barbed wire fence. In a telephone interview after the accident, the pilot stated that he had been unaware that the proper procedure to use in checking for the accumulation of carburetor icing with a constant-speed propeller was to check manifold pressure drop. He was also not aware that as ice accumulated in the carburetor throat, resulting in a gradual reduction of power, that the propeller governor would keep the rpm constant as long as it was able to flatten the pitch of the propeller. He was also unaware that a drop in EGT may also be an indication of ice accumulating in the carburetor throat.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

the pilot's improper use of the carburetor heat while attempting to determine if there was ice accumulating in the carburetor throat. Factors include flight in conditions conducive to carburetor icing, and a fence running across the field in which the forced landing took place.

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