Event Description
During an approach to a helipad, the pilot turned right and descended at about 1,300 feet per minute until intercepting the standard approach profile. As collective pitch was increased, rotor rpm immediately dropped to 90 percent. The low rotor rpm horn and light activated, and the pilot fully lowered the collective. The company primary pilot, seated in the rear, reported no engine-out or warning horn activation. At that time, the pilot estimated altitude between 100 and 150 feet above ground level and airspeed at about 60 knots.
Emergency Landing
The pilot declared an emergency to the air traffic control tower and turned left toward an open area between terminals 5 and 6. Realizing insufficient altitude to clear terminal buildings, the pilot pulled collective pitch, which further decayed rotor rpm but provided additional lift. The primary pilot shouted multiple times to lower the collective. As the helicopter descended toward the intended landing point, a twin-engine turboprop airplane entered the ramp area, causing the pilot to veer right to avoid it. The pilot fully lowered the collective and decided to perform a run-on landing with little or no flare. All remaining collective pitch was pulled before impact.
The helicopter contacted the ground in a tail-low attitude, slid forward approximately 60 feet, and made a 180-degree turn. The right front chin bubble shattered on impact. Both landing gear skids were forced upward through the cabin, and the helicopter came to rest on its belly. The pilot attempted to shut off the engine by rolling the throttle past idle cutoff but could not manipulate it. The fuel shutoff valve, generators, and battery were then turned off.
Post-Accident Examination
The pilot stated no prior problems with the helicopter before the accident. The engine was removed and run in a test cell. Due to a test cell breakdown, the run could not be completed; however, an uncommanded decrease in rpm was observed immediately before the failure. The fuel control unit and power turbine governor were removed and bench tested. Static bench testing indicated both components were slightly out of calibration. According to Rolls Royce, the irregularities noted on the power turbine governor were consistent with a high-time governor and/or impact or vibration damage. The governor had 246.5 hours remaining before the next overhaul. The Rolls Royce investigator reported that the discrepancies might result in a 2 percent increase or decrease of N2 rpm with a corresponding change in collective lever position. Fuel control discrepancies were described as insignificant deviations.
Engine Testing
The engine was transported to Scottsdale, Arizona, where a complete and normal run was accomplished. During the test, several aggressive accelerations and decelerations were conducted with no discrepancies noted. The test sequence included initial idle, seal run-in to maximum power, five power point checks, governor droop, and a final idle setting. The engine performance met all required specifications. The power turbine governor was subsequently bench tested again by Allied Signal.