Aircraft Accident/Incident Report

Taft, California 93268
Tuesady, November 30, 1999 13:45 PST

During a forced landing after an engine failure, the helicopter struck a standpipe, shearing its cross tube, and rolling onto its side. The pilot was in the process of picking up an 800-pound sling load on a 100-foot-long line. As his load reached about 90 to 100 feet agl, the engine quit. He released his load, turned to the right to avoid people and equipment on the ground, and entered autorotation. The conditions at the accident site were dusty and gritty. The engine teardown revealed that a second stage compressor vane had failed in fatigue, which resulted in a catastrophic failure of the compressor section. All first stage vanes were intact, and all third, fourth, fifth, and sixth stage vanes exhibited some degree of foreign object damage (FOD). The plastic coating on the first and second stage vanes exhibited erosion that exceeded the maximum allowable limits specified by the Rolls-Royce Allison 250-C20 Series Operation and Maintenance Manual. The first stage compressor blades were eroded, with the leading edges rolled over and scalloped. Metallurgical examination of the failed vanes revealed that they met all chemical and manufacturing process specifications. According to the maintenance records, a 300-hour inspection had been performed on the engine 130.1 flight hours before the accident. The manufacturer recommends a compressor case inspection be accomplished every 300 hours when operating in a corrosive environment. No evidence was found in the maintenance records of compressor washes being performed as recommended by the manufacturer.

The fatigue failure of a second stage compressor vane due to erosion, which resulted in a catastrophic engine failure. An inadequate inspection of the compressor section by company maintenance personnel during the last 300-hour inspection was also causal in this accident. The maintenance personnel's failure to conduct the periodic recommended compressor washes was a factor.