Aircraft Accident/Incident Report

Grace, Idaho 83241
Monday, September 18, 1995 12:00 MDT

During log slinging operations the restricted category UH-1L rotorcraft's T53-L-13B military engine experienced a total loss of power. The pilot dropped the log load and autorotated into a small, upsloping, cleared area within the surrounding wooded terrain landing hard. Postcrash examination of the engine revealed that the centrifugal impeller had separated due to fatigue cracking in one of the drain holes. An Airworthiness Directive (AD) had been issued relative to the -08 impeller but did not include the -07 impeller (installed in the accident engine). The -07 and -08 impellers are essentially identical with the exception that the -07 impeller is found on military variants of the engine whereas the -08 is found only on civilian variants. As the -07 impeller was not included in the AD, the operator was not required to conduct the appropriate inspections described in the mandated service bulletin. Additionally, the AD did not require a cycle count for the impeller as addressed in the service bulletin, thus rendering the service bulletin unusable even if it had been mandated for the -07 impeller.

the fatigue failure of the centrifugal impeller and the lack of suitable terrain for a forced landing. Factors contributing to the accident were: the lack of required compliance with the FAA Airworthiness Directive by the operator, the insufficiently defined FAA procedure within the AD (failure to include the -07 impeller and establish a cycle count program), and inadequate rotor RPM.