NTSB Identification: ANC07LA088.
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Accident occurred Saturday, August 18, 2007 in Big Lake, AK
Probable Cause Approval Date: 03/31/2008
Aircraft: Piper J-3, registration: N98875
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The local instructional flight was on an extended, low power descending approach to a remote airstrip when the engine lost power. Remedial actions to restore engine power, including pulling the carburetor heat on, did not restore engine power. The flight instructor seated in the rear seat of the tandem, two seat airplane, realized the airplane was too low to reach the airstrip, and he took the controls from the front seat pilot. The instructor made an off-airport emergency landing in soft terrain, and the airplane nosed over. Postaccident inspection disclosed ample fuel and no preimpact mechanical problems. The front seat pilot related that he did not have the carburetor heat on until the loss of engine power occurred, and the instructor told him to turn it on. He also said that there were low, wispy clouds in the area. A local weather report indicated that the temperature was 57F, and the dew point was 52F. When these values are entered into a carburetor icing probability chart, the results are in the "Serious Icing" category. Carburetor ice likely formed inside the carburetor, which resulted in the loss of engine power. Carburetor heat becomes ineffective once the engine has lost power.

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

The flight instructor's delayed instructions to apply the carburetor heat, and his inadequate supervision. A factor contributing to the accident was carburetor icing conditions.

Full narrative available

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