Accident Summary
On May 13, 2009, at 0908 Pacific daylight time, a Rotorcraft Development Corporation UH-1B helicopter, registration N843M, collided with a building during takeoff from Richvale Airport in Richvale, California. The commercial pilot, the sole occupant, sustained serious injuries. The helicopter, owned and operated by AvAg Inc., sustained substantial damage. The flight was conducted under 14 CFR Part 91 as a local repositioning flight in visual meteorological conditions. No flight plan had been filed.
Flight Details
The helicopter had undergone a 100-hour inspection the day prior to the accident. The purpose of the flight was to reposition the helicopter to a nearby ramp area. The pilot, who was also the owner of AvAg, was the sole occupant.
Pilot Account
During an interview with an FAA inspector and a Bell Helicopter representative, the pilot stated that after lifting into a hover and initiating forward movement, he immediately noticed that the controls felt "ratchety" and stiff. He described the sensation as similar to operating the helicopter with the hydraulic system turned off. An AvAg helper who was observing the startup from in front of the helicopter saw the pilot struggling to maintain control.
The pilot reported that he was unable to touch back down by lowering the collective or control direction with the cyclic. His primary focus was on keeping the helicopter level and avoiding lateral oscillations. The helicopter moved forward and collided with a hangar about 160 feet from its original position, having climbed approximately 15 feet. The fuselage became embedded in the building, while the tail section came to rest on the ground below. The pilot stated he does not remember the collision or events after impact.
Post-Accident Examination
Following recovery, an examination was conducted on June 30, 2009, with an FAA inspector and a Bell technical representative present. Control continuity was established from cyclic and collective controls to the actuators, but the anti-torque control tube was cut during recovery, and the pilot anti-torque pedals were impact damaged, preventing continuity verification. The hydraulic switch was found in the "ON" position, and electrical continuity was confirmed for both the switch and the hydraulic caution light bulbs.
The hydraulic pump and servos were sent to a testing facility. The servos and their valves functioned normally. The hydraulic filters were clean, and the shutoff/overpressure valve was within parameters. During pump testing, the check valve was noted to be installed on the pressure side. With the check valve removed, the pump passed all tests. However, with the check valve installed (as it was originally), the pump delivered only 3.85 gallons per minute at 940 psi, below the specified 5.25 gpm. According to a Bell representative, maintenance manuals and drawings show the check valve on the pressure side, indicating correct installation.
Additional Information
A Bell representative stated that during initial startup after assembly or servicing, it is common to cycle all controls for up to two minutes to purge air and achieve smooth control motion. He noted that ratcheting or binding in the cyclic, often accompanied by a howling noise, may occur during this process. The Bell Flight Test Procedure Manual for various models (including the UH-1 series) contains notes that control forces may vary considerably if the hydraulic system is not completely purged of air, and that control feel may be irregular, spongy, loose, or restricted until air is purged.
The AvAg Director of Maintenance stated that during the 100-hour inspection, the hydraulic system is normally serviced (drained, filters replaced, and refilled), after which a pilot cycles the controls to bleed air. The AvAg helper reported that the pilot spent about five minutes on the ground after engine start, but was unsure how many times the controls were cycled. The operator did not file a required Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2).