ISLIP, NY, USA
N211PD
Eurocopter AS-350
The pilot was completing transition training in the helicopter with a flight instructor. The pilot initiated a simulated hydraulics failure out of sequence with the flight-training guide and flew the helicopter to the ground without incident. With hydraulics still disabled, the pilot was instructed to hover-taxi approximately 100 feet, perform a left pedal turn, and taxi back. The pilot successfully hovered forward; however, during the turn to hover back to the start point, the pilot could not maintain control of the helicopter. The instructor attempted recovery, but the helicopter rolled and the main rotor blades struck terrain. Orientation of the helicopter following the turn resulted in a 14-knot tailwind. Examination of the wreckage revealed no pre-impact anomalies. Testing of the hydraulic servos revealed high fluid flow rates, but no operational deficiencies. Approximately 1 year after the accident, the helicopter manufacturer removed in ground-effect maneuvers with the hydraulics off from their flight-training guide.
On August 3, 1999, at 1131 Eastern Daylight Time, a Eurocopter AS-350 helicopter, N211PD, operated by the Suffolk County Police Department, was substantially damaged during collision with terrain at the Long Island MacArthur Airport (ISP), Islip, New York. The certificated flight instructor (CFI) and the commercial pilot received minor injuries. Visual meteorological conditions prevailed for the training flight that originated at ISP, approximately 1045. No flight plan was filed for the flight conducted under 14 CFR Part 91. According to a sergeant of the Special Patrol Bureau, the purpose of the flight was to provide aircraft transition training to the commercial pilot. The pilot entered the traffic pattern and performed a run-on landing to the sod area parallel to runway 33. The maneuver was performed hydraulics off, to simulate a Hydraulic Servo-Control System failure. With hydraulics still disabled, the pilot was instructed to hover-taxi approximately 100 feet, perform a left pedal turn, and taxi back. In a written statement, the pilot said: "Once on the ground [the CFI] instructed [me] to pick up the aircraft to a hover and taxi approximately 100 feet. I completed the maneuver satisfactorily and without incident. [The CFI] then instructed me to do a pedal turn and taxi back. I did a pedal turn and hovered approximately 10 feet when I felt something wasn't right with the controls. I asked [the CFI] to get on the controls with me and both of us tried to level out the aircraft, but to no avail. The helicopter kept pitching up and left. The blades struck the ground and the helicopter ended up on its right side." In a written statement, the CFI outlined the purpose of the flight and described the simulated hydraulics failure and the subsequent hydraulics-off maneuvers that were performed. He said: "After hovering forward for approximately 100 feet [I] instructed [the commercial pilot] to do a hovering turn and to hover the helicopter forward in the opposite direction. [The commercial pilot] turned the helicopter and proceeded to hover forward for a distance of approximately 10 feet. It was at this time that [she] announced that she was experiencing unusual feedback in the flight controls. "[I] immediately got on the controls with [her] and the helicopter began an uncontrollable roll to the left while at a hover. "As the helicopter continued its uncontrollable rolling motion to the left and reached an approximate angle of 30 degrees, [I] tried to level the helicopter by using both hands to attempt to pull the cyclic control to the neutral/level position. The helicopter continued to roll to the left and subsequently the main rotor blades struck the ground. The helicopter eventually came to rest on its right side." Both pilots reported the engine continued to run after the helicopter came to rest. In a written statement, an airport employee said she witnessed the accident from the second floor of a building at the base of the control tower. A radar tower approximately 30 feet tall was along her line of sight between the building and the flight path of the helicopter. She said: "I saw one of the Suffolk County Police helicopters fly east to west higher than the radar. I saw the helicopter turn to the left towards the southeast. As it was making this turn, it was losing altitude. As the helicopter came down, it started leaning towards the right side. "It looked like it was coming down too fast and I thought to myself that it was going to crash. I saw the rotor blade hit the ground. The helicopter was a little more than half way over on its side when the blade hit and it looked like the skid gear was about eight feet off the ground. As soon as the blade hit, a large dust cloud rose up and I couldn't see any more." Examination of the wreckage by Federal Aviation Administration (FAA) aviation safety inspectors revealed no pre-impact anomalies. The cyclic and collective servos (3) were removed for examination and testing at Hawker Pacific Inc, Sun Valley, California. Bench checks and functional tests were performed on all three servos on November 3 and 4, 1999. The functional areas measured were rated as "Accepted" or "Rejected". All three servos measured "high actual flow rates" and were rejected in that functional area. The left cyclic servo and the collective servo were rejected in the Speed Test Hydraulic mode area. The collective servo was also rejected for exceeding the leak rate by one drop of fluid per measured cycle. All three servos were graded "Accepted" in all other test areas including the "By-Pass Valve and Lock Operation Test". According to the Eurocopter AS-350 Instruction Manual, Servo Actuators and Hydraulic System, Loss of Hydraulic Pressure: "When the hydraulic pressure drops below the bypass spring load, the bypass pin is pushed into the servo actuator input lever slot and chambers A and B are simultaneously interconnected. The input lever is thus blocked and the pilot activates the control in mechanical mode." In a telephone interview, the chief pilot at American Eurocopter explained the simulated hydraulic servo-control system failure in a training environment, and the component responses in the system based on student and instructor control inputs. According to the chief pilot and the Eurocopter flight training syllabus, activation of the "HYD Test" button initiates the simulated emergency as it depressurizes the system, illuminates the "HYD" light, and activates the warning horn. Accumulators to allow for adjustment of the flight controls to attain 40 to 60 knots airspeed, provide 30 to 45 seconds of normal hydraulic boost. Once the desired airspeed is reached, the hydraulic cut-off switch on the collective control stick is activated by the student pilot to cut-off hydraulic supply, eliminate residual pressures, and isolate the servos from the hydraulic system. According to the flight training syllabus: "Upon reaching the desired airspeed in level flight, the student will disable the hydraulic accumulators by using the hydraulic cut-off located on the collective pitch lever. This will cause the servos to immediately lose pressure..." The chief pilot was questioned about the likelihood of a servo hard-over malfunction after the hydraulic system was disabled. He said: "It is impossible for the servo to have a hard-over once you isolate the hydraulic system. Once you dump the pressure, the pin drops, locks the pilot valve, and you have a mechanical linkage. The servo becomes a rigid part of the push-pull tube." A review of flight records by an FAA inspector revealed the commercial pilot had accumulated 417 hours of total flight experience, all of which was in helicopters. The commercial pilot had accumulated 70 hours in the AS-350. A review of the CFI's flight records revealed over 7,800 hours of total flight experience, all of which was in helicopters. The CFI had accumulated about 111 hours in the AS-350. Examination of the flight-training syllabus provided by American Eurocopter on August 5, 1999, revealed that step 2 of the procedure describes landing and repositioning of the helicopter with the hydraulics off. According to the syllabus: "Landing with hydraulics off will be accomplished by making a shallow (4-6 degrees) approach over a clear area and landing to the ground with slight forward speed. After landing, instruct the student pilot to establish a hover, reposition the aircraft to a new area, and land the aircraft without hydraulics." In a telephone interview on October 30, 2000, the chief pilot said the flight-training syllabus no longer requires hovering or repositioning of the helicopter with the hydraulics off. When asked what precipitated the change, he explained that it was for uniformity of training worldwide. That company flight training was patterned after the parent company in France. Additional questions regarding hydraulics-off training were forwarded through Eurocopter's Safety Department to their chief pilot. Answers to the questions included the following: "1. Why was the portion of the AS350 training syllabus regarding the pick-up to a hover and repositioning of the aircraft with the hydraulics disabled deleted from the revised training syllabus? A: To align our training syllabus with the Eurocopter France training. 2. When was the above maneuver discontinued in training of customers? A: The maneuvers were official changed in July 2000. The updated training syllabus was printed November 2000. 3. What other, if any, hydraulics off maneuvers were deleted from the syllabus and when? A: Servo transparency - July 2000. 4. Were any new hydraulic off maneuvers added to the newly published AS350 training syllabus? A: OGE simulated hydraulic failure. 5. If so, when and why were they added? A: July 2000, maneuver was not being taught. 6. When there is a change in a hydraulic system training maneuver or procedure, how does AEC notify previously trained Pilots and Instructor Pilots that the maneuver has changed? A: During pilot recurrent training and at the yearly Instructor Pilot Seminar." According to the written statements of both pilots, the hydraulics-off training maneuvers were initiated when the commercial pilot "...turned off the hydraulics switch located on the collective which dumps the accumulators and load feedback is felt immediately." According to the flight-training manual at the time, actuation of the hydraulic cut-off switch on the collective was performed only after the "Hyd Test" button was actuated, and the airspeed was adjusted. Winds reported at ISP 25 minutes after the accident were from 030 degrees at 14 knots.
The pilot's loss of control during hydraulics-off hovering flight and the instructor's inadequate supervision of the maneuver. A factor was the tailwind.
Source: NTSB Aviation Accident Database
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