WPR15FA205

The loss of translation/rotational power between the engine and the transmission due to the severe wear of the forward spline portion of the lower coupling drive shaft. The reason for the severe wear of the forward spline could not be definitively determined due to fire damage and the loss of associated components, which were not located during the investigation.

The instructor and student were conducting a night orientation flight. According to a witnesses who worked for the operator, about 15 minutes after the helicopter departed, he heard what sounded like an engine rollback and the helicopter making an autorotation. This was followed by the sound of an increase in engine rpm and the drive belts squealing, culminating with the sound of the helicopter making a loud thud-type noise. Another witness stated that the engine sounded rough and that the helicopter was making a high pitch whining/squealing sound, after which it went silent. A third witness also heard the helicopter making high pitch noise just before the accident. The helicopter was subsequently located in an open field near the departure airport; a postcrash fire erupted, which consumed the helicopter. A postaccident examination of the lower coupling drive shaft showed evidence of severe wear completely around the forward spline that extended beyond the root of the spline teeth. Severe wear of the forward spline teeth could have been caused by a loss of alignment between the engine and the drive shaft or an inflight loss of lubrication in the rubber boot. The rubber boot that retains grease for the forward spline portion of the drive shaft was not recovered and was presumed missing. Loss of grease coverage for the forward spline, either from a rupture of the rubber boot or a loss of the clamp for the rubber boot, could cause sudden inflight wear and overheating of the spline teeth. Severe wear of the forward spline portion of the lower coupling drive shaft most likely led to sudden and complete loss of translational/rotational power between the engine and the transmission. The reason for the severe wear of the forward spline could not be definitively determined due to fire damage and the loss of associated components, which were not located during the investigation.

Flight Instructor On July 2, 2015, an autopsy on the flight instructor was performed at the Office of The State Medical Examiner, Clackamas, Oregon. The examination revealed that the cause of death was the result of blunt force chest trauma. The FAA's Civil Aeromedical Institute in Oklahoma City, Oklahoma, performed toxicology testing on the flight instructor. The test was negative for carbon monoxide, ethanol, and tested drugs. Acetone, which was not quantified, was detected in the blood. Testing for cyanide was not performed. Pilot Undergoing Instruction On July 2, 2015, an autopsy on the pilot receiving instruction was performed at the Office of The State Medical Examiner, Clackamas, Oregon. The examination revealed that the cause of death was the result of blunt force chest trauma. The FAA's Civil Aeromedical Institute in Oklahoma City, Oklahoma, performed toxicology testing on the flight instructor. The test was negative for carbon monoxide and ethanol. Testing for cyanide was not performed. Pheniramine, a drug commonly used for hay fever, was detected in the urine but not in the blood. At 2253, the weather reporting facility at the McMinnville Municipal Airport (MVV), McMinnville, Oregon, which is located about 8.5 nautical miles south-southwest of the accident site, reported wind 260° at 4 knots, visibility 7 miles, sky clear, temperature 22°C, dew point 14°C, and an altimeter setting of 29.94 inches of mercury. Certified Flight Instructor (CFI) The CFI, age 31, possessed a commercial pilot certificate with rotorcraft-helicopter, and instrument helicopter ratings. He also possessed a flight instructor certificate with rotorcraft-helicopter, and instrument rotorcraft ratings. The CFI's most recent flight review was successfully accomplished on March 13, 2015, and his most recent second-class airman medical certificate was awarded on August 28, 2014, with the stated limitation, "Must wear corrective lenses for near and distant vision." A review of the CFI's personal flight records revealed that he had accumulated a total flight time of 354.6 hours, 278.1 hours in the same make and model as the accident helicopter, and 123.7 hours of flight instruction given. Additionally, the CFI had accumulated 122.5 hours, 66.8 hours, and 3.8 hours in the last 90 days, 30 days, and 24 hours respectively. The CFI was given a company evaluation flight by the operator on February 9, 2015, and a company Federal Aviation Regulation Part 141 check ride on March 13, 2015. The CFI began performing flight instructor duties for the operator on April 22, 2015. This was the CFI's initial employment as a flight instructor. Pilot Undergoing Instruction (PUI) According to records provided by the operator, the PUI, age 29, received his student pilot certificate concurrent with his airman third-class airman medical certificate on April 17, 2015, with no limitations. According to the PUI's personal flight logbook, he had logged a total of 41.6 hours of flight time, of which 38.4 hours were in helicopters, 6.0 hours was as pilot in commend/solo flight time, and 35.8 hours were in the same make and model as the accident helicopter. Additionally, the PUI had flown 32.0 hours and 19.1 hours in the preceding 90 days and 30 days respectively. The aircraft and engine were examined at the facilities of Nu Venture Air Service, Dallas, Oregon, on August 20, 2015, under the supervision of the NTSB IIC and FAA inspectors. Participants to the examination included representatives from Sikorsky Aircraft and Lycoming Engines. The results of the examinations revealed the following. Airframe Photos of the site provided by a Portland Flight Standards District Office aviation safety inspector revealed that the helicopter was severely damaged by a postcrash fire. All components appeared to be closely located to the main fuselage. The frame tubing exhibited multiple fractures, kinks and bends. It also showed it had been exposed to the fire, with all paint burned away. Both forward cluster fittings that attach the cross beam were separated from the frame tubing. Other portions of the frame were separated by fractures of the tubing or welds. The aft mast support strut was intact. The right support strut exhibited minor mid span bending, and the left strut appeared straight. All exhibited thermal damage. The tail boom was separated from the fuselage, appeared intact with minor damage, with no blade strikes apparent. The forward bulkhead attachment lug was fractured and was consistent with overload separation. There was minor fire damage to the paint on the forward end, and oily soot deposits further aft. The tail gear box adapter remained in the boom with several attach bolt holes deformed. The tail stinger was separated at the adapter. Both tail boom support struts exhibited a compression buckle at mid-span, and separated attach fittings at the center attachment to the tail boom. The horizontal stabilizer forward attach fitting was fractured. The vertical stabilizer was crushed and bent aft with vegetation remaining in the folded sheet metal. The landing gear and crossbeams were severely damaged. The aft crossbeam was largely intact, separated from the frame, and exhibited significant bending, and was fractured and separated at the right side cluster fitting; additionally, the right outboard end was burned away. All landing gear dampers were separated at one or both ends and several were burned. The left skid was fractured and separated just forward of the forward skid strut. The right skid appears to have been intact but suffered melting and burning. The support struts were separated at the crossbeam attach areas, and several suffered significant fire damage and burning. The root ends of all three main rotor blades remained attached to the main rotor head; the outer airfoils were cut away to facilitate recovery. Each blade was relatively intact, and exhibited minor impact damage. Two blades exhibited thermal damage, with some of the aluminum airfoil consumed. The main rotor head was intact and remained attached to the drive shaft. The swashplate and rotating scissor links were intact. The rotor head turned freely in the mast bearing. Both tail rotor blades were intact, with one having remained attached to the hub via the strap pack. The opposite blade had separated thru a fracture at the inboard end of the hub spindle and fractured the strap pack also. Tip damage and some airfoil compression damage was present with the separated blade tip cap gone. The pitch change links were attached, although the separated blade link was badly bent. Both blades exhibited thermal damage to the paint. The tail rotor fork and teetering bolt were intact, and the assembly teetered properly. The fork was equipped with the elastomeric bearings. The pitch control unit was intact, rotated freely, slid in and out on the pinion, and was attached to the pitch links. The control bell crank was engaged in the pitch control housing and attached to the tail gear box and the control rod. The inboard rubber boot was consumed by fire. The tail rotor gear box (TGB) remained attached to the tail boom with elongation of several of the attachment bolt holes. The TRG was rotated and exhibited continuity from the input to the TGB output. The chip detector was not examined. The tail rotor drive shaft (TRDS) was separated at the forward end from the main gear box (MGB) pinion drive spline. The retention nut exhibited damage to the flange. MGB drive adapter splines were intact. The forward TRDS splines were intact, and the cup contained grease. The forward end of the TRDS exhibited no torsional buckling with some minor tearing and flattening, and was fractured and separated at the point where it passed through the forward bulkhead. The aft spline joint at the TGB was intact, remained assembled and exhibited continuity through the TGB. The main gearbox (MGB) hous