Accident Overview
An aircraft experienced an engine flameout after encountering forecasted icing conditions. The pilot had previously selected alternate air but was unable to maintain altitude due to the power loss. During an attempted air restart, the turbine outlet temperature (TOT) rose to approximately 520 degrees, the engine would not accelerate, and quickly lost power. A forced landing was subsequently executed in mountainous terrain.
Induction System Details
The induction system incorporates both normal and alternate air paths. The normal path utilizes two ram air scoops that direct air to an air box, which then feeds the engine inlet. Selection of the alternate air path directs engine bleed air to close the ram air scoop doors and open an alternate air door located on the bottom of the cowl. Air then circulates around the engine and passes through a spring-loaded door on the rear of the air box before reaching the engine.
Post-Accident Examination
On-site examination revealed that the ram air doors were closed and the cockpit lever was positioned to alternate air. The alternate air door open air line was found to have a loose B-nut fitting at the valve. The checklist calls for the use of alternate air during an air start. The supplemental type certificate (STC) holder could not produce any engineering or flight test data to validate that the engine would produce sufficient vacuum to open the air box spring-loaded door during an air start.
Probable Cause
The engine flamed out after encountering forecasted icing.