History of Flight
On November 13, 2015, at 1648 central standard time, a Robinson Helicopter R44II, registration N449MC, was substantially damaged during an in-flight collision with trees and terrain near Alpine, Texas. The pilot and one crewmember sustained serious injuries; two additional crewmembers sustained minor injuries. The helicopter was registered to and operated by Concho Aviation LLC under 14 Code of Federal Regulations Part 91 as an aerial survey flight. Day visual meteorological conditions prevailed, and the flight was not operated on a flight plan. The local flight originated from a private ranch about 17 miles south of Alpine.
GPS data indicated that two flights were conducted before the accident flight. The first flight departed about 0830 and concluded about 1051, tracking eastbound momentarily before proceeding west. The second flight departed about 1106 and concluded about 1320, tracking eastbound and continuing in that direction.
Crewmembers reported that during one takeoff, the helicopter was unable to climb high enough to clear power lines bordering the takeoff/landing area on three sides. The pilot turned around and departed to the west, where there were no power lines, but a one-story building was present. One crewmember estimated the landing skids cleared the building by about 15 feet.
According to one crewmember, the pilot commented that during the morning takeoff, the helicopter "wouldn't go." The pilot explained that the helicopter had full fuel and four occupants, and the low rotor speed warning came on, which can occur if the rotor blades reach full pitch for the given conditions. The pilot added that rotor speed needs to be increased by increasing airspeed or initiating a descent.
Crewmembers stated they were conducting wildlife surveys and predator control at the time of the accident. The pilot was maneuvering when the low rotor speed warning activated. The pilot attempted to regain control by descending into a small canyon, but his efforts were unsuccessful, and the helicopter impacted trees and then the ground. The pilot did not recall the accident sequence.
GPS data showed the accident flight departed at 1515, with the final data point at 1648. During takeoff, the helicopter initially tracked eastbound, reversed course westward momentarily, then departed to the east. The helicopter proceeded north and west with multiple turns and course reversals. The maximum extent was 3.00 miles north-northwest of the departure point; the accident site was 2.31 miles north-northwest. GPS altitudes ranged from 4,504 to 5,357 feet. The elevation of the departure point was about 4,507 feet; the accident site was about 4,763 feet.
Shortly before the accident, the helicopter completed a 360-degree turn at about 4,800 feet and approximately 20 knots. About 20 seconds before the end of data, it entered a gradual left turn from 4,805 to 4,763 feet. The accident site terrain consisted of rolling hills, low brush, and vegetation.
Personnel Information
The pilot held a commercial pilot certificate with helicopter, instrument helicopter, and single-engine land airplane ratings; the airplane rating was limited to private pilot privileges. He also held a flight instructor certificate with a helicopter rating. A second-class airman medical certificate was issued on October 15, 2014, with no limitations. The pilot's logbook included an endorsement to act as pilot-in-command of a Robinson R44 helicopter, dated February 14, 2014, under FAA Special Federal Aviation Regulation (SFAR) No. 73.
According to the operator's accident report, the pilot had 735 hours total flight time, with 697 hours in helicopters and 228 hours in Robinson R44 II helicopters. About 90 hours were flown within the preceding 30 days and about 12 hours within the preceding 24 hours, all in Robinson R44 II helicopters. The pilot completed a flight review on September 27, 2014, in a Robinson R22 Beta II helicopter.
SFAR No. 73 required a flight review in a Robinson R44 within the preceding 12 calendar months to act as pilot-in-command. This review must include specific abnormal and emergency procedures flight training.
Aircraft Information
The accident aircraft was a Robinson R44 II helicopter, serial number 13340. It was a four-place design with a two-blade teetering main rotor system and fixed skid-type landing gear. Anti-torque and directional control were provided by a two-blade teetering tail rotor system. Conventional cyclic/collective controls were utilized, and the main rotor controls were hydraulically boosted.
A Lycoming IO-540-AE1A5 engine, serial number L-34923-48E, powered the helicopter. It was a six-cylinder, horizontally opposed, normally aspirated, air-cooled, fuel-injected engine producing 260 horsepower at 2,800 rpm, derated to 245 hp for takeoff (5 minutes) and 205 hp for continuous operation. Engine cooling was provided by a direct-drive blower. Power was transferred to the rotor drive system through four V-belts; an electric actuator adjusted belt tension.
Maintenance records showed the most recent annual inspection was completed on April 8, 2015, at 502.91 hours total airframe time. R44 Service Bulletin SB-89 was complied with on April 26, 2015. An annual/100-hour engine inspection was completed on November 6, 2015, at 605.9 hours total airframe/engine time.
Meteorological Information
Weather recorded at Alpine-Casparis Municipal Airport (E38), about 16 miles north of the accident site, at 1635: wind from 160 degrees at 10 knots, 10 miles visibility, clear sky, temperature 20°C, dew point 1°C, altimeter 30.22 inches of mercury. The published elevation at E38 was 4,514 feet; density altitude was about 5,770 feet.
Wreckage and Impact Information
The accident site consisted of sparsely-wooded, rolling hills with low vegetation and brush. The helicopter came to rest on its left side. Main rotor blades remained attached to the hub. The tail boom was separated, fragmented, and located at the site. Tail rotor blades remained attached to the hub. Landing skids remained attached but were deformed and fragmented.
The NTSB did not travel to the site; a postaccident examination was conducted after recovery. The cockpit/cabin area was compromised, with more extensive damage on the left side. Center and aft fuselage structure appeared intact but deformed. The forward tail boom structure remained attached to the upper frame but was deformed and separated immediately aft of the mounting point. The tail boom was separated into six sections, including the forward section attached to the aft fuselage. Sections exhibited scuff marks consistent with main rotor blade strikes. Horizontal and vertical stabilizers remained attached to the aft tail boom section, with buckling, deformation, and crushing damage.
The main rotor mast and fairing appeared intact. Engine-drive train V-belts appeared intact and properly installed. Main rotor gearbox, mast, and hub appeared intact. Rotation of the drive shaft produced corresponding rotation of the main rotor mast, confirming gearbox continuity. The sprag clutch/free wheel unit rotated smoothly. Main rotor blades exhibited gradual bending with localized deformation and creasing.
Cockpit cyclic control remained attached to the dislocated floor structure. Forward-aft cyclic control continuity was confirmed from cyclic stick to main rotor mast. Left-right cyclic torque tube was separated consistent with overstress failure; continuity was confirmed aft of separation to the mast. Collective control appeared intact except for an overstress separation at the aft end. Separations in the main rotor mast fork assembly and pitch change links appeared consistent with overload. Tail rotor/anti-torque pedals were deformed but attached. Push-pull tube assemblies associated with tail rotor control in the cockpit area separated consistent with overstress. Control continuity was continuous from aft of cockpit area separations to the aft fuselage. The tail rotor control push-pull tube common to aft fuselage and tail boom was separated into six segments; forward and aft segments remained attached to bell crank assemblies. Tube segments were deformed, fracture surfaces consistent with overload.
Tail rotor gearbox remained attached and appeared intact. Rotation of the tail rotor shaft produced corresponding rotation of the input drive shaft, with no binding. Tail rotor blades remained attached; pitch change links and bellcrank were intact. Tail rotor drive shaft separated at forward and aft flex-couplings; both couplings were deformed, fracture surfaces consistent with overstress. The drive shaft separated into two sections; the forward section was not with the wreckage during postaccident examination.
The engine remained attached to the mount and appeared undamaged. Cooling baffling was intact. The engine and drive train were rotated via the fanwheel with V-belts in place. Lower spark plugs exhibited normal combustion signatures. Internal engine, valve train, and accessory section continuity was confirmed. Compression and suction were obtained at all cylinders. Magnetos remained secured; timing was within specifications; both produced spark at all leads. Fuel flow was confirmed from fuel pump output line during rotation. Fuel injection servo remained attached and appeared undamaged; throttle and mixture cables remained attached. Bench testing did not reveal anomalies consistent with loss of engine power. Fuel flow values were within specification at high power settings. Disassembly revealed a small amount of non-ferrous debris on both sides of the diaphragm. Fuel strainer and vent screen were intact and free of debris.
Tests and Research
A weight and balance calculation based on information from pilot, crewmembers, and operator indicated the gross weight at takeoff was approximately 2,465 lbs., with longitudinal and lateral center-of-gravity locations of 94.5 inches and 0.03 inch, respectively. Maximum gross weight was 2,500 lbs. Center-of-gravity locations were within loading limits specified in the pilot's operating handbook.
Performance data related to the out-of-ground effect (OGE) hover ceiling indicated that under the current loading and atmospheric conditions, the OGE hover ceiling was approximately 4,100 feet pressure altitude – about 4,400 feet mean sea level.
Organizational and Management Information
The accident flight was operated by Concho Aviation, LLC, a helicopter services company based in Sterling City, Texas. Because the flight was for aerial survey (wildlife survey and predator control), the operator was not required to comply with 14 CFR Part 119 or Part 135. The occupants, in addition to the pilot, were classified as crewmembers for regulatory purposes. The flight was governed by basic requirements of 14 CFR Part 91.
Additional Information
The Pilot's Operating Handbook, Section 3 – Emergency Procedures, provided guidance for a low rotor speed condition: "LOW RPM HORN & CAUTION LIGHT – A horn and an illuminated caution light indicate that rotor RPM may be below safe limits. To restore RPM, immediately roll the throttle on, lower collective and, in forward flight, apply aft cyclic. The horn and caution light are disabled when the collective is full down."
As noted in the FAA Helicopter Flying Handbook, hover performance varies depending on ground effect. Ground effect increases rotor efficiency and reduces power required to hover in ground effect up to about one rotor diameter. Above this height, more power is required to hover out of ground effect. Effective translational lift (ETL) is achieved between 16 and 24 knots horizontal movement; above ETL speed, the rotor system operates in relatively undisturbed air.