GAA17CA151 · Robinson Helicopter R44 UNDESIGNAT

The pilot in the skid-equipped helicopter reported that he had performed an agricultural application flight. The helicopter was within 100 lbs of the maximum gross weight at the time of the accident. The helicopter was headed south, and the pilot made a left turn to the west, and the helicopter began to settle with power. The pilot noticed the low rotor rpm, and the helicopter touched down on the soft dirt surface and rolled over. The helicopter sustained substantial damage to both rotor drive systems and the fuselage and tailboom.

In an interview with National Transportation Safety Board investigator-in-charge, the pilot stated that the helicopter was about 20 ft above ground level when he noticed the low rotor rpm horn and that the airspeed was about 20 knots. He recalled that, when he made the left turn, he was operating with a tailwind. He added that the design of the hopper was not approved by the Federal Aviation Administration to be jettisoned.

The pilot reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.

Additional Information

According to the Federal Aviation Administration (FAA) Helicopter Flying Handbook FAA-8083-21A (HFH) (pg. 2-4, para. 5), turns in a helicopter increase the load factor exponentially, ultimately increasing the power requirement that is necessary to maintain the helicopter's altitude. Left pedal turns increase the quantity of anti-torque produced by the tail rotor, by demanding additional power from the 260-brake horsepower engine. Pilot flight control inputs demanding more power than the engine is capable of producing, with respect to the atmospheric conditions, adversely affects the helicopters ability to sustain its altitude. Available engine power is directly correlated to main and tail rotor RPM.

FAA-8083-21A (pg. 7-2, para. 5), "Factors Affecting Performance," stated:

The wind direction is also an important consideration. Headwinds are the most desirable as they contribute to the greatest increase in performance. Strong crosswinds and tailwinds may require the use of more tail rotor thrust to maintain directional control. This increased tail rotor thrust absorbs power from the engine, which means there is less power available to the main rotor for the production of lift.

FAA-8083-21A (pg. 2-4, para. 6), "Weight," stated:

To overcome this additional load factor, the helicopter must be able to produce more lift. If excess engine power is not available, the helicopter either descends or has to decelerate in order to maintain the same altitude. The load factor and, hence, apparent gross weight increase is relatively small in banks up to 30°. Even so, under the right set of adverse circumstances, such as high DA, turbulent air, high gross weight, and poor pilot technique, sufficient or excess power may not be available to maintain altitude and airspeed.

FAA-8083-21A (pg. 2-5, para. 1), "Weight," further stated:

Regardless of how much weight one can carry or the engine power that it may have, they (helicopters) are all susceptible to aerodynamic overloading. Unfortunately, if the pilot attempts to push the performance envelope the consequence can be fatal. Aerodynamic forces effect every movement in a helicopter, whether it is increasing the collective or a steep bank angle. Anticipating results from a particular maneuver or adjustment of a flight control is not good piloting technique. Instead pilots need to truly understand the capabilities of the helicopter under any and all circumstances and plan to never exceed the flight envelope for any situation.

Verbatim NTSB analysis and probable cause from the NTSB dataset