Darby, MT, USA
N369HW
MD HELICOPTER 369A
The pilot reported that he purchased the turbine-powered helicopter about 5 weeks before the accident and departed from his private airstrip for a brief local personal flight. During the approach for landing, when the helicopter was about 200 to 300 ft above ground level (agl), he added some power, and the engine responded normally. Shortly thereafter, he conducted a height-velocity check with satisfactory results. The pilot then slowed the helicopter to a descending hover with the engine running at an unspecified speed above flight idle. The pilot stated that, when the helicopter was about 10 ft agl, he increased the throttle setting, but the engine did not respond. He added collective to slow the descent, but the helicopter landed hard. Postaccident on-scene examination and system testing did not reveal evidence of any mechanical anomalies that would have resulted in a loss of engine power. The engine was tested in its as-removed condition and satisfactorily met all operational test and power calibration criteria with no anomalies or deficiencies noted. Review of the helicopter manufacturer's operating manual revealed that, during all phases of normal flight, the throttle should be in the full open (normal) position and should not be moved by the pilot. With the throttle in the full open position, a governor automatically increases and decreases engine power to maintain rotor rpm as the pilot raises and lowers the collective. According to the manufacturer, when the throttle is not in the full open position, the governor will not maintain rotor rpm, and full power will not be available. The pilot's statement that he increased the throttle setting about 10 feet agl indicates that he was manipulating the throttle contrary to the operating manual procedures, and this is likely the reason he was unsuccessful in stopping the helicopter's descent.
HISTORY OF FLIGHTOn April 2, 2013, about 1100 mountain daylight time, a McDonnell Douglas 369A helicopter, N369HW, was substantially damaged during a hard landing on private property in Darby, Montana. The owner-pilot received serious injuries, and his three passengers received minor injuries. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no Federal Aviation Administration (FAA) flight plan was filed for the flight. According to the pilot, he departed from his ranch/airstrip with his son-in-law and two grandchildren, and they flew about 1/2 hour on a local sightseeing flight. Near the end of the flight, during the approach for landing, when the helicopter was about 200 to 300 feet above ground level (agl), the pilot added some power, and the engine responded normally. Shortly thereafter, he conducted his "60-60" check, which assured that the helicopter was at 60 mph at 60 feet agl. The pilot then stopped the helicopter's forward velocity, and began descending vertically, with the engine running at a speed above idle. At an altitude of about 10 feet agl, the pilot increased the throttle setting, but the engine did not respond. He realized that they would then land hard, so he added collective to slow the descent. The helicopter impacted the ground; the tail rotor, tail boom, and all main rotor blades separated from the helicopter. The left skid partially collapsed; the helicopter remained upright, but leaning to the left. There was no fire, and all four occupants exited the helicopter. The helicopter was recovered and stored in the pilot's hangar for examination. PERSONNEL INFORMATIONThe pilot held multiple ratings and certificates, including airline transport pilot and rotorcraft-helicopter. His most recent FAA second-class medical certificate was issued in May 2012. Despite multiple requests, the pilot did not provide a completed NTSB Form 6120.1, "Pilot/Operator Aircraft Accident/Incident Report." AIRCRAFT INFORMATIONFAA information indicated that the helicopter was manufactured in 1970, originally as a Hughes Helicopter OH-6 for the US military. It was issued an FAA "Standard Airworthiness Certificate" in the "normal" category as a McDonnell Douglas Helicopter Incorporated 369A in March 2006. The pilot purchased the helicopter in late February 2013. The helicopter was equipped with an Allison (Rolls-Royce) 250-C20C series turbine engine. Maintenance records indicated that the engine was converted from an Allison T63-A720 to the M250-C20C in March 2006, when it had a total time (TT) of 1,757.8 hours. The records indicated that no recent heavy maintenance or component changes had been accomplished. The engine's most recent inspection was completed on February 26, 2013, at an engine TT of 1,901.9 hours. METEOROLOGICAL INFORMATIONThe 1100 automated weather observation at 6S5, located about 18 miles north of the accident site, included winds from 050 degrees at 5 knots, visibility 10 miles, temperature 10 degrees C, dew point 0 degrees C, and an altimeter setting of 30.08 inches of mercury. AIRPORT INFORMATIONFAA information indicated that the helicopter was manufactured in 1970, originally as a Hughes Helicopter OH-6 for the US military. It was issued an FAA "Standard Airworthiness Certificate" in the "normal" category as a McDonnell Douglas Helicopter Incorporated 369A in March 2006. The pilot purchased the helicopter in late February 2013. The helicopter was equipped with an Allison (Rolls-Royce) 250-C20C series turbine engine. Maintenance records indicated that the engine was converted from an Allison T63-A720 to the M250-C20C in March 2006, when it had a total time (TT) of 1,757.8 hours. The records indicated that no recent heavy maintenance or component changes had been accomplished. The engine's most recent inspection was completed on February 26, 2013, at an engine TT of 1,901.9 hours. WRECKAGE AND IMPACT INFORMATIONThe helicopter came to rest about 100 yards to the west of the pilot's hangar, in the pilot's landing zone, which was a turf field. The approximate site geographic coordinates were 45° 55' 56" North, 114° 07' 15" West, at an elevation of 4,000 feet above mean sea level. The helicopter remained upright, but leaned significantly to the left, which permitted the main rotor blades to contact the ground. The helicopter sustained significant damage, but remained upright. There was no fire. ADDITIONAL INFORMATIONOn-Site Examination On April 9, 2013 the wreckage was examined on-scene by personnel from the FAA, McDonnell Douglas Helicopter, and Rolls-Royce. It had been recovered from the landing zone to the pilot's hangar. The helicopter was situated upright on a trailer. The left landing gear was fractured and the lower left forward fuselage was damaged in the area of the landing gear strut attachment. The right skid remained intact. Impact damage was also noted to the engine left clam shell door. The aft top of the pylon displayed evidence of main rotor blade contact. The tail boom separated just forward of the horizontal/vertical fins, and damage was consistent with main rotor blade strikes. The tail rotor gearbox remained attached to the aft segment of the tail boom/empennage section, but both tail rotor blades had fracture-separated just outboard of the root fittings. The tail rotor hub had separated from the tail rotor gearbox, and was not recovered. All four main rotor blades separated from the main rotor head, fracturing at the hub and tearing all "TT" (Torsion-Tension) straps. Three of the four blades remained in one piece from root to tip. The fourth blade had fractured into two pieces at approximately mid-span. All four blades displayed aft bending from root to tip. The damage to the main rotor hub, main rotor blades and tail rotor assembly was consistent with a power-on condition at the time of the main and tail rotor blade strikes. The engine remained securely attached to the airframe, in its normal installed position. No visible impact damage to the engine was noted. A visual and tactile examination of all engine pneumatic, fuel and oil lines was conducted; all "B" nuts and associated fittings were found to be at least finger tight. Oil and fuel line interface connections between the engine and airframe were examined; all were found to be at least finger tight, with no evidence of leakage. A vacuum check of the fuel system was conducted in accordance to Rolls-Royce OMM specification. The system held the required pressure for longer than the test-specified 2 minutes, which satisfied the criteria for a successful ("pass") leak check. The fuel tank was then partially drained of fuel. Approximately 10 gallons were removed from the tank, and additional fuel was noted to remain in the tank. The engine was removed from the airframe. Manual rotation of the N1 drive train confirmed that the drive train was free and continuous from the starter generator pad to the compressor. Manual rotation of the N2 drive train confirmed that it was free and continuous from the power take-off gear to the No. 4 power turbine wheel. The engine was sent to Rolls-Royce Indianapolis for operational testing. Engine Operational Testing On May 21, 2013 "Run as Received" testing was conducted on the subject engine at Rolls-Royce Indianapolis, Indiana. Testing was conducted to the new engine specifications in Rolls-Royce Production Test Specification 795. The engine was removed from the container and placed onto an engine stand for preparation and pre-run examination. Nothing was discovered during the examination that would preclude operational testing. The engine was placed into the test cell, where test cell instrumentation and control links were affixed to it. The engine started successfully within the specification time- and temperature-limits, and it stabilized at ground idle power. The engine was run at idle until it warmed up, and all vibration measurements remained within specification limits. The engine was accelerated to flight idle power, and then cycled through a series of timed accelerations and decelerations. The accelerations, decelerations, and governor droop checks were all within allowable limits. The engine was then operated and allowed to stabilize at six discrete power settings for power calibration purposes; the engine performed within specification at all six of those test points. At the conclusion of testing, the engine was shut down normally. A total test run time of 2 hours 15 minutes was accomplished. Normal Operating Procedures The twist-grip throttle control, integrated into each collective pitch stick, is a three-position device. The three positions are cut-off, idle, and normal. "Cut-off" is used to shut down the engine, "idle" is used for on-ground operation, and "normal" is used for all flight operations. During all operations, the main rotor speed, designated "NR," is automatically held constant by the engine and its control system. During all phases of normal flight, the pilot never manipulates the throttle; engine power is indirectly controlled via the collective pitch system, and to a much lesser extent, via the N2 governor. With the throttle in the "normal" position, the pilot can control engine N2 speed, through a very limited range, by the N2 governor switch. N2 speed is set to 101 percent for engine runup, takeoff, and all flight conditions except hover. The designated hover N2 speed is 103 percent. According to the manufacturer, when the throttle is not in the full open position, the governor will not maintain rotor rpm, and full power will not be available.
The pilot's failure to arrest the landing descent due to his incorrect use of the throttle, which resulted in a hard landing.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
