ANITA BAY, AK, USA
N44094
SIKORSKY C54A
THE HELICOPTER EXPERIENCED A #2 ENGINE FAILURE DURING A HOVER FOR LANDING WITH AN EXTERNAL LOAD. EXAMINATION OF THE ENGINE SHOWED THAT THE POWER TURBINE DISC REMAINED INTACT. HOWEVER, ALL THE TURBINE BLADES WERE BENT, BROKEN, OR MISSING THE ENGINE CASE WAS SEVERED IN TWO PARTS IMMEDIATELY ADJACENT TO THE PLANE OF ROTATION OF THE POWER TURBINE. THE MANUFACTURER'S TBO WAS 1800 HRS. THE COMPANY HAD A MILITARY TBO EXTENSION, APPROVED BY THE FAA, TO 2100 HRS. THE ENGINE HAD A TOTAL TIME OF 2058 HRS AT THE TIME OF THE FAILURE.
On September 23, 1993, at 0900 Alaska daylight time, a wheel equipped Sikorsky CH54A helicopter, N44094, registered to and operated by CRI Helicopters, of Appley Valley, California, experienced a total mechanical loss of engine power on the number 2 engine while hovering with an external load of logs at Anita Bay, Alaska. The helicopter set down the external load and flew to its service area 1 mile away. The two commercially certificated pilots were not injured and the helicopter received minor damage. The external load operation was operating under 14 CFR Part 133. No flight plan was filed and visual meteorological conditions prevailed. According to the Pilot-in-Command, they had just come to a hover for landing when they heard a bang and a loud hissing. they also experienced a slight yaw. While the Pilot-in-Command was landing the Co-pilot stated they had lost the number 2 engine. Examination of the number 2 engine showed that the engine case was severed adjacent to the power turbine wheel. The turbine disc was in one piece, however, the turbine blades were missing, broken, and bent. According to Leon Dailey, Director of Maintenance (DM) for CRI Helicopters in Apple Valley, the helicopter was operating under the restricted category because it was a military surplus aircraft. The engine, serial number 672453, had received an extension, extending the time to be overhauled (TBO) from 1800 hours to 2100 hours. The TBO extension was originally issued by the military and was approved by the Federal Aviation Administration. According to the Federal Aviation Administration there is no cycle requirement or requirement to adhere to TBO times when operating under 14 CFR Part 91, 91D, or 133 (external load operations). According to CRI they have 5 CH54A helicopters. Three are operational and two are in maintenance. None of those engines have a TBO extension. The total time on the failed engine was 2058.7 hours. According to Leon Dailey, DM, CRI, the helicopter engine had no recorded history of previous overspeed conditions or other anomalies. The turbine disc was not submitted for metallurgical examination because of the smearing and mallatizing of the turbine blade fracture surfaces and the turbine wheel's proximity to its extended TBO limit. According to Leon Dailey, a turbine blade separated from the turbine disc and exited the engine. The unbalanced condition of the power turbine wheel cut the engine case in two.
THE SEPARATION OF THE TURBINE BLADE FROM THE POWER TURBINE DISC.
Source: NTSB Aviation Accident Database
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