Accident Summary
On August 28, 2013, about 1030 mountain standard time, a Bell Helicopter Textron 206L-1, registration N2018R, sustained substantial damage during an off-airport emergency landing approximately 14 miles west of Payson Airport in Payson, Arizona. The helicopter was registered to GM Leasing Company LLC and operated by Airlift Helicopters under Part 135. The commercial pilot reported a partial loss of engine power while cruising at about 1,500 feet above ground level and performed an autorotation. During the descent, the pilot maneuvered to avoid obstacles and noted a low rotor warning light and an N1 indication dropping to about 70 percent. The helicopter landed hard, and the tail boom separated. The pilot sustained serious injuries; none of the five passengers were injured. Visual meteorological conditions prevailed, and a company VFR flight plan was filed for the cross-country corporate flight from Scottsdale Airport to Flagstaff Pulliam Airport.
Examination Findings
Postaccident examination of the airframe revealed continuity of main rotor flight controls from the cockpit to the main rotor pitch links. Tail rotor flight control continuity was established from the left anti-torque pedal assembly to the tail boom separation, but continuity from the pilot's right anti-torque pedals could not be established due to a fractured control tube; however, continuity was present across the fracture. Drive continuity was confirmed from the main rotor system through the transmission and engine to the tail rotor driveshaft at the tail boom separation. Both main rotor pitch change links were fractured. The tail rotor rotated freely. The landing skid was spread, and cross-tubes were rotated aft. The fuselage, doors, windows, and main cabin were intact. When electrical power was applied, the engine over-temp light illuminated. No anomalies were observed with flight, navigation, or propulsion instruments.
The engine, a Rolls-Royce 250-C30P (replacing the original 250-C28B), remained attached with no visible damage. It was shipped to Rolls-Royce for examination. During a test run, erratic and higher-than-specified turbine vibrations occurred, and the engine could not produce specified power. A possible power turbine governor malfunction was considered, but replacing the governor did not resolve the issue. Disassembly revealed thermal damage to the outer portions of all first-stage turbine blade tips and localized melting on three stage-one nozzle vanes. Metallurgical examination indicated localized metal temperatures exceeded 1149 degrees Celsius, far above the maximum continuous TOT limit of 716°C and maximum takeoff TOT of 768°C. The investigation could not determine when the over-temperature occurred. Blade hardness and composition met specifications, with no evidence of fatigue progression.
Additional testing of the power turbine governor, fuel control unit, fuel nozzle, thermocouple harness, and MGT gauge found all met specifications. Postaccident examination revealed no additional evidence of a mechanical malfunction that would have precluded normal operation.
Weight Analysis
The helicopter's maximum gross weight per the Rotorcraft Flight Manual is 4,150 pounds. The pilot reported a gross weight of 4,000 pounds at the time of the accident. Fuel burn calculations indicated about 210 pounds of fuel were consumed since takeoff, yielding a computed takeoff gross weight of about 4,210 pounds. The NTSB investigator-in-charge calculated the takeoff gross weight using the empty weight, reported occupant weights, 70 gallons of fuel, and 21 pounds of baggage, resulting in about 4,222 pounds—exceeding the manufacturer's limitation. Density altitude at cruise altitude was calculated to be about 9,500 feet.