WPR15LA159

The commercial pilot was conducting an external load logging flight in the helicopter. A review of maintenance records revealed that, on the day of the accident, the engine had been replaced with an overhauled engine. Following the maintenance, the pilot completed one logging cycle without incident. The pilot reported that, about 50 minutes into the second cycle, she heard a loud screeching/grinding noise followed by a muffled "bang." The low rotor rpm horn sounded, and she initiated an autorotation. The helicopter touched down, impacted trees, rolled down sloped terrain, and then came to rest. A postaccident examination of the engine's particle separator assembly revealed that it was intact and installed properly on the air inlet section; however, the inlet guide vanes exhibited signatures consistent with foreign object damage, and a material consistent with a towel was found within the vanes. Given the damage signatures and the found material, it is likely that maintenance personnel did not adequately inspect the engine area after installing the overhauled engine and left a towel in its compressor section, which the engine subsequently ingested and resulted in a total loss of power.

On May 07, 2015, about 1750 Pacific daylight time, a Garlick UH-1B, N46969, experienced a total loss of engine power near Kettle Falls, Washington. R & R Conner Aviation, the registered owner, was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 133 as an external load logging flight. The commercial pilot, the sole occupant, sustained minor injuries; the helicopter sustained substantial damage. The flight departed from the landing zone in the area at about 1700. Visual meteorological conditions prevailed, and no flight plan was filed.During a telephone conversation with a Safety Board investigator, the pilot stated that she had been performing logging operations for the past four days. The engine had been replaced the day of the accident. Following the maintenance, the operator's chief pilot conducted a short test flight. Thereafter, the long-line was attached to the helicopter and the pilot conducted a 50-minute logging cycle. She returned to the landing zone and refueled, planning on another 1 hour 20-minute logging cycle. The operation was configured with the log landing was located at the base of a steep hill, and the hookers were located at the top. After about 50 minutes into the cycle, equating to about 22 picks, the pilot was maneuvering the helicopter up the mountain toward the hookers. When the helicopter was about three quarters of the way up the mountain, about 200 to 300 feet above the tree line, she heard a loud screeching/grinding noise followed by a muffled "bang." The low rotor rpm horn sounded and she initiated an autorotation, maneuvering the nose of the helicopter to touch down upslope. The helicopter impacted trees and after touching down, began to roll down the slope. She braced herself through several rolls until the helicopter came to a stop. Upon exiting out the bubble window, she noticed the engine was smoking. A post accident examination was conducted of the engine and airframe. The complete examination report with embedded pictures is contained in the public docket for this accident. Drive train continuity was verified from the tail rotor drive shaft to the transmission. Rotation of the tail rotor drive shaft in the direction of rotation (free wheel via sprag clutch) produced a corresponding rotation of the main rotor. There were was no evidence of airframe mechanical malfunctions or failures. The helicopter is equipped with a Lycoming T53-L-13B engine, serial number LE-17588. The T53 series engines are shaft turbine engines with a two stage, free type power turbine and a two stage gas producer turbine that drives a combination axial centrifugal compressor. The external areas of the engine appeared intact with no visible damage. The interior of the engine exhaust tail pipe showed signs consistent with internal overheating. The power turbine section could not be rotated manually and various power turbine blades were damaged. The particle separator assembly appeared intact andinstalled properly on the air inlet section. Examination of the inlet guide vanes (IGV) revealed material appearing to be consistent with a towel within the various IGVs. The trailing edges of the IGVs appeared to be displaced forward and distorted, and displayed signs consistent with foreign object damage. Material consistent with a towel was also observed in the compressor section. The helicopter records indicated that the newly-overhauled engine was installed on the day of the accident.