History of Flight
On October 2, 2014, about 1255 central daylight time, a Bell 206B helicopter, registration N49746, experienced a hard landing following a loss of tail rotor effectiveness near Woodsboro, Texas. The pilot and two passengers sustained serious injuries. The helicopter sustained substantial damage during a subsequent roll over. The helicopter was registered to and operated by an individual doing business as Heartland Helicopters under Part 91 as an aerial observation flight. Day visual flight rules conditions prevailed; no flight plan was filed. The flight originated from Alfred C 'Bubba' Thomas Airport (T69) near Sinton, Texas, about 1200, and was destined for Beeville Municipal Airport near Beeville, Texas.
The flight's purpose was a laser examination of a pipeline to detect methane gas. The pilot reported flying between 35 and 40 meters above ground level. The helicopter suddenly yawed to the right without warning. The pilot recalled a warning horn, which he believed was a low rotor rpm warning. The pilot stated that wires were to the right and building structures to the left. The helicopter yawed, the pilot applied left pedal, and a loss of tail rotor effectiveness occurred. The helicopter hesitated turning right for a short period, then continued a full revolution to the right. The pilot intended to guide the helicopter away from wires and structures but impacted the ground and rolled onto its right side.
A passenger reported hearing another passenger guide the pilot to turn right near power lines. He felt a change in helicopter position, heard a decrease in engine RPM followed by a warning horn, and heard the pilot say he had a low tail rotor warning. The helicopter spun, and he braced for impact.
Personnel Information
The pilot, age 47, held an FAA airline transport pilot certificate with airplane multi-engine land rating, commercial privileges in airplane single-engine land, rotorcraft helicopter, and instrument helicopter, and a flight instructor certificate with airplane single-engine and rotorcraft helicopter ratings. He also held a flight engineer certificate with turbojet rating. He held a second-class medical certificate dated August 15, 2014, with a limitation for corrective lenses. His most recent flight review was on May 20, 2014. He reported 13,916 total flight hours, including 2,376 hours in rotorcraft and 35 hours in the same make and model as the accident helicopter.
Aircraft Information
N49746 was a 1976 Bell 206B helicopter, serial number 1928, powered by a 420-shaft horsepower Rolls Royce 250-C20B engine (serial number CAE-834605). It was a five-place, single main rotor helicopter with a tail-mounted anti-torque rotor. The helicopter was maintained under a manufacturer's inspection program; its last inspection was a 100-hour inspection on June 5, 2014, at which time it had 18,323.2 total flight hours. According to NTSB report FTW81DRA33, the helicopter was involved in a prior accident on May 19, 1981, when it sustained substantial damage during a takeoff accident in the Gulf of Mexico.
The helicopter was fitted with a Pergam Aerial Laser Methane Assessment (ALMA) device. The system includes an on-board laptop, electronic laser-control system, GPS receiver, and a belly-mounted optical unit with a laser, reference channel, and three digital video recording cameras.
A fuel receipt indicated the helicopter was serviced on October 2, 2014, with 60.1 gallons of Jet A fuel at T69.
Meteorological Information
At 1353, weather recorded about 17 miles from the accident site at Aransas County Airport near Rockport, Texas: wind 170 degrees at 10 knots gusting to 21 knots, visibility 10 statute miles, few clouds at 1,600 feet, scattered at 2,400 feet, broken at 2,900 feet, temperature 32°C, dew point 26°C, altimeter 29.86 inches of mercury. Field elevation about 24 feet MSL.
Wreckage and Impact Information
The helicopter impacted a field near Woodsboro, Texas, and was moved to a salvage yard. Examination at the salvage yard revealed damage consistent with the helicopter coming to rest on its right side. The mast exhibited overload separation. Main rotor blades showed impact damage. The transmission rotated when manipulated by hand. The tailboom was separated from the fuselage; the tail rotor driveshaft inside was separated, consistent with being cut by recovery personnel. The tailboom deformation was consistent with contact with terrain during a rollover to the right. Tail rotor blades were intact. Skids showed overload deformation and separations. A tear was observed in the lower portion of the fuel cell. Both fuel boost pumps were intact and pumped fuel when powered. Airframe filters showed no anomalies. The tail rotor and main rotor systems moved when the turbine blades were rotated by hand. No pre-impact anomalies were observed. The engine was separated and examined; disassembly revealed no anomalies that would have precluded engine operation. The engine's fuel control and governor were tested and found operational.
Additional Information
FAA Advisory Circular 90-95 and the Helicopter Flying Handbook describe loss of tail rotor effectiveness (LTE) as an uncommanded, rapid yaw towards the advancing blade, caused by aerodynamic interaction between main rotor and tail rotor, not mechanical failure. LTE is associated with factors such as airflow interference, main blade vortices, turbulence, high power settings, slow forward airspeed, and certain wind directions. Flight activities like pipeline patrols and low-speed aerial work are at higher risk.
Tests and Research
The ALMA system components (Lenovo ThinkPad, hard drives, PCMCIA card, Garmin GPSMAP 296) were sent to the NTSB Vehicle Recorder Laboratory. No usable data was extracted from the GPS, hard drives, or PCMCIA card. The laptop contained flight position data, which was decoded and plotted. The data showed the helicopter flew south, executed a left 270-degree turn, turned right 90 degrees, then left 90 degrees, with groundspeeds between 50-70 knots and altitudes from about 200 feet MSL down to 70 feet, then back to 120 feet. At about 1255, the ground track headed north, groundspeed decreased to about 15 knots, altitude dropped from 130 to 55 feet, then back to 80 feet. In the last 10 seconds, groundspeed varied between 9.4 and 25.2 knots, altitude decreased to the 50-foot range. The last recorded point was about 4.1 miles southeast of Woodsboro, on a track of 304° true, altitude 53 feet MSL, groundspeed 15.4 knots.