FTW99LA105

The main rotor blades struck and severed the tailboom of the helicopter during a hard landing following a loss of engine power. The helicopter departed the airport to the southwest and climbed to 400 feet AGL. The pilot turned the helicopter downwind and leveled the aircraft. He set 'cruise power' and the engine 'spooled down.' The pilot performed an autorotation to a muddy, grassy field and landed hard. The engine was test run and it was determined that the fuel scheduling was incorrect as the turbine outlet temperature would exceed the maximum allowed. After replacement of the fuel control unit, the engine was 'found to meet new engine performance at all guarantee test points.' The fuel control unit was functionally tested and operated within service limits. The reason for the loss of engine power could not be determined.

On April 5, 1999, at approximately 1000 central daylight time, a Bell 206L-1 helicopter, N255AL, was substantially damaged during a forced landing following a loss of engine power during takeoff near Shawnee, Oklahoma. The instrument rated commercial pilot and five passengers were not injured. The helicopter was registered to and operated by Air Flite Inc., of Seminole, Oklahoma. Visual meteorological conditions prevailed for the Title 14 Code of Federal Regulations Part 135 on-demand air taxi flight and a flight plan was not filed. The aerial observation flight was originating at the time of the accident.

According to the 7,500-hour pilot, the purpose of the flight was to provide a tour of the city to local politicians. The helicopter departed the airport to the southwest and climbed to 400 feet agl. He turned the helicopter downwind and leveled the helicopter. The pilot stated the he set "cruise power" and "the engine spooled down." He turned the helicopter into the wind as he initiated an autorotation to an open field. During the flare/touchdown sequence of the autorotation, the main rotor blades struck and severed the tailboom. The helicopter came to rest upright in a grassy, muddy field one mile from the airport. The pilot added that the engine continued to run at ground idle speed upon completion of the autorotation. An FAA inspector who visited the accident site reported that fuel was present "from the aircraft firewall to the fuel pump."

The pilot reported that at the time of the accident, the winds were from 230 degrees at 30 knots, gusting to 35 knots.

The 435-horsepower Allison A250-C28B turboshaft engine had accumulated 5,411.4 hours since new, 1,159.4 hours since its last overhaul, and 1.5 hours since the last annual inspection. On April 14, 1999, the engine was examined under the supervision of an FAA inspector at Dallas Airmotive Inc., of Dallas, Texas. The pneumatic system was tested and no leakage was observed. The engine was placed in a test cell and started. During two timed "snap acceleration[s] from flight auto to takeoff, the fail safe temperature limit on the test stand was tripped causing the engine to shut down." It was determined that fuel scheduling was incorrect. The Allied Signal/Bendix fuel control unit (model DP-T3, p/n 2524738-34) was replaced with a slave fuel control unit, provided by Dallas Airmotive. According to the engine manufacturer, "the engine was [then] found to meet new engine performance at all guarantee test points."

The fuel control unit was functionally tested under the supervision of an FAA inspector at the Allied Signal Aerospace facilities in Burbank, California. The functional test revealed that the unit operated within service limits. According to the manufacturer, no anomalies were found that would have "prohibited it from operating normally" at the time of the accident.