PHILADELPHIA, PA, USA
N61TV
Aerospatiale AS-350B
The pilot reported that he lifted the helicopter off the dolly, and as he air taxied, it became uncontrollable. During the subsequent landing, the helicopter rolled over on its right side. Both the pilot and passenger reported hearing a warning horn and seeing a light on the instrument panel illuminated. Additionally, the passenger heard and felt a rumble and thought the helicopter rotated nose left once or twice prior to touchdown. A check of the hydraulic system failed to reveal any failure or malfunction. An uncommanded loss of hydraulic pressure could not be induced. A check of SDRs revealed no previous uncommanded loss of hydraulic pressure. The checklist called for the three position engine throttle to be brought to the ON position after engine start. In a flight test conducted by the manufacturer, a takeoff was initiated with the throttle not advanced all they way to the ON position. Once airborne, a warning light illuminated on the instrument panel, the low rotor warning horn sounded, and a low rumble was felt and heard. The helicopter remained controllable, although increased movements were required for all controls.
On July 28, 1997, about 0630 eastern daylight time, a Eurocopter AS-350B helicopter, N61TV, was substantially damaged while departing from the Penn's Landing Heliport, Philadelphia, Pennsylvania. The certificated commercial pilot and camera operator received minor injuries. Visual meteorological conditions prevailed for the aerial observation flight. No flight plan had been filed for the flight which was conducted under 14 CFR Part 91. In the NTSB Pilot/Operator Aircraft Accident Report, the pilot stated: "...I did my normal preflight on N61TV. I found no discrepancies. I towed the A/C out of the hanger on a dolly...I started the A/C...completed all systems checks and lifted off. I heard a warning horn sound & warning lights flash at the same time. I experienced a total loss of hydraulics while repositioning to the "H" for departure. The A/C was extremely difficult to control and I tried to perform a normal landing away from the dolly. The A/C landed on the right skid and rolled over on its right side. I secured all elect. switches, shut down eng, and shut emergency fuel valve off. I then exited the A/C...." In a follow-up telephone interview, the pilot reported he was in a 5 foot hover when the hydraulic warning light illuminated, and the flight controls locked. Control was difficult. He lowered the collective and the helicopter contacted the ground on the right skid and rolled over. In a written statement the cameraman stated: "...Paul lifted off the dolly and started to nose toward the big H. As he did we started to climb. Before we got to the H a rumble sound shook the whole bird then the light and horn alert came on. The helicopter then started to fishtail - at this point the machine was back up and I looked out eye level to the 2nd story window. As the chopper was fishtailing and vibrating Paul and I looked at each other and knew we were in trouble - I saw Paul grip with both hands the stick and try to control the bird as much as possible but to no avail it spun to the left then fishtailed again and landed hard on the right skid and crashed down onto the pad...." In a follow-up telephone interview, the cameraman reported that after liftoff, he felt a vibration followed by the horn sounding and a warning light illuminating. The helicopter spun to the left making at least one 360 degree turn, possibly more, he wasn't sure. The helicopter touched down on the right skid while rotating, and rolled over to the right. The investigation revealed the helicopter was equipped with a single hydraulic pump, mounted on the main rotor transmission, which supplied hydraulic power to the rudder pedals, collective, and cyclic. The hydraulic pump was run by rubber belts which were in place and secure. The hydraulic system was not in need of servicing. There were two methods to disengage the hydraulic system. One method was to depress the hydraulic isolation switch on the end of the collective. If depressed, the hydraulic accumulator would be bypassed, and all hydraulic pressure would be removed from the rudder pedals, cyclic, and collective, in about 3 seconds. During this method, the hydraulic low pressure light would illuminate; however, there would be no associated warning horn. The second method to disconnect the hydraulic power would be to depress the hydraulic test button on the instrument console. Hydraulic pressure would be immediately shut off to the rudder pedals, but the accumulator would continue to supply hydraulic pressure to the cyclic and collective for 45 seconds, to 2 minutes, dependent upon pilot input to the flight controls. The warning horn would sound and the low hydraulic pressure light would illuminate. The investigation revealed that the warning horn would sound for either low rotor RPM, or low hydraulic pressure. If the hydraulic system was deactivated using the isolation switch on the end of the collective, then the horn circuit for low hydraulic pressure was disabled. The horn would sound for low rotor RPM, but there was no low rotor RPM light. The main rotor head and tailboom were removed and the engine was run. The hydraulic system was engaged and disengaged utilizing both the hydraulic isolation switch on the collective, and the hydraulic test switch, with no malfunctions noted. A check of the electrical wiring leading to and from the hydraulic disconnect switches was performed. No discrepancies were noted. The investigation was unable to induce an uncommanded loss of hydraulic power. A check of Service Difficulty Reports (SDRs) for hydraulic systems on the AS-350 failed to find any occurrence of unexplained loss of hydraulic power. A small piece of rotor blade was found imbedded in the trailer dolly used for parking of the helicopter. It was located in an area of broken wood. The part was examined at American Eurocopter's facility in Grand Prairie Texas, with an inspector from the Federal Aviation Administration (FAA) in attendance. The piece was identified as part of a main rotor blade. The helicopter's throttle was mounted on the floor to the left of the pilot, and had three positions, OFF, ON, and EMERGENCY, each with a locking detent. The OFF position was used when the engine was shut off. The ON position was the governing range for flight. The start checklist called for the throttle to be advanced to ON during the starting process. A flight test was conducted by the Chief Accident Investigator for American Eurocopter. In the flight test, he attempted a lift off with the throttle at a lesser position that the ON detent. The helicopter became airborne, followed by a main rotor RPM droop. The low rotor warning horn sounded, and the engine bleed valve light illuminated when the collective was raised, and extinguished when it was lowered. In addition, a low rumble was felt and heard in the cockpit. He further noted that the cyclic and collective flight controls were found to be responsive, but not as they would have been at the normal operating main rotor RPM. The tail rotor was also responsive, but required increased pedal movement. During an interview after the accident, the cameraman reported hearing a rumble followed by the helicopter spinning nose left for one or two revolutions. The pilot had no memory of the rotations or of hearing the rumble. The pilot's records revealed that he had completed the AS-350 flight and ground school on April 22, 1996.
failure of the pilot to follow the checklist and verify the throttle was in the ON position before lift-off, which resulted in low rotor RPM and loss of control, while attempting to hover/taxi.
Source: NTSB Aviation Accident Database
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