History of Flight
On June 27, 2011, at 1223 central daylight time, a Robinson R22 BETA helicopter, N7779M, struck trees and impacted terrain near Del Valle, Texas. The pilot, the sole occupant, was fatally injured. The helicopter sustained substantial damage and a post-impact fire occurred. The flight was conducted under 14 CFR Part 91 as a personal cross-country trip, originating from Taylor, Texas (T74) at approximately 1205, en route to Luling, Texas. Visual meteorological conditions prevailed; no flight plan was filed.
Two witnesses standing on the south side of the Colorado River observed the helicopter flying north to south just above the trees. As it crossed the river, they heard a loud "pop" or "bang" and saw an object separate from the helicopter and fall into the river. They then saw smoke from the crash and ran to the scene.
Crew Information
The pilot, aged 60, held a private pilot certificate with airplane single/multiengine land, instrument-airplane, and rotorcraft-helicopter ratings. His second-class medical certificate, issued October 2, 2009, required corrective lenses for near and intermediate vision. He had approximately 220 helicopter flight hours, all in the Robinson R22, with 15 hours in the previous 90 days and 3 hours in the previous 30 days. His last flight review was on August 27, 2010.
Aircraft Information
The helicopter, N7779M (serial number 1229), was a 1989 Robinson R22 BETA powered by a Lycoming O-320-B2C engine (serial L-15943-39A) rated at 131 horsepower. The engine was overhauled on October 14, 2010, and a 2,200-hour airframe overhaul was completed on December 30, 2010, at a total time of 2,294.8 hours. During the airframe overhaul, several components were replaced, including the main rotor gearbox, swashplate, gearset, hub, driveshaft, clutch shaft, bearing assembly, sprag clutch, tail rotor blades and hub, tail rotor gearbox and pitch control, tailcone assembly, horizontal stabilizer, and welded frame. An annual inspection was then performed, and the main rotor blades were replaced per a manufacturer service bulletin.
Meteorological Information
The weather at Austin-Bergstrom International Airport (KAUS) at 1153 indicated wind from 190 degrees at 12 knots gusting to 19 knots, visibility 10 statute miles, scattered clouds at 3,600 feet, temperature 34°C, dew point 22°C, and altimeter 29.93 inHg.
Wreckage and Impact Information
The helicopter struck trees and terrain on the south side of the Colorado River. The burnt wreckage came to rest at the base of a large tree, with a piece of tail boom skin found in the tree. One main rotor blade was located approximately 780 feet from the wreckage, and the other blade was found about 975 feet in the opposite direction. Both blades were intact without leading edge damage. The river was searched by the Texas Department of Public Safety, but nothing was recovered. Examination of the rotor hub revealed that only parts from two different main rotor blade attachment bolts were found: the head of one bolt and the nut and shank of the other. The head of the second bolt and the nut and shank of the first were missing. No other missing components were noted.
Medical and Pathological Information
An autopsy conducted by the Travis County Medical Examiner's Office attributed the pilot's death to blunt force injuries. Toxicology tests detected no drugs or ethanol. The FAA's Civil Aerospace Medical Institute also performed toxicology screening, which corroborated the Medical Examiner's findings; carbon monoxide and cyanide tests were not conducted.
Tests and Research
Components including the inboard portions of both rotor blades, rotor hub, grips, pitch linkages, swashplate, and transmission were examined at the NTSB metallurgical laboratory. The hub displayed overload fractures on both sides. The main rotor blades tested negative for blood and bird residue. The metallurgical examination revealed that the main rotor hub rotates counterclockwise about the teeter bolt. It noted that the Robinson R22, like other semi-rigid rotor helicopters, is susceptible to mast bumping. Robinson Helicopters describes "mast bumping" as teetering beyond allowable clearance, causing contact between the hub and main rotor shaft. "Low-G mast bumping" is specific to two-bladed teetering rotor systems where the rotor disc becomes unloaded, often due to a cyclic pushover, and can lead to main rotor shaft separation. Damage signatures in the controls, main rotor head, and blades were consistent with both "Low-G mast bumping" and "low rotor RPM rotor stall."
Additional Information
Radar data from KAUS approach control showed the helicopter departing Taylor at 1205 and proceeding toward Luling, with altitude varying between 1,200 and 1,400 feet msl. After the accident, the operator flew the same route and had radar track him to the top of the tree at the impact site. The operator calculated that the helicopter descended from 1,100 feet msl to ground (less than 400 feet msl) in less than five seconds, yielding a descent rate exceeding 7,000 feet per minute. The operator noted that autorotations do not produce descent rates above 2,000 feet per minute.