LAX07GA217

a loss of control for undetermined reasons, which resulted in an uncommanded roll and subsequent collision with terrain. Contributing factors in the accident were the flying pilot's failure to request assistance from the second pilot in a timely manner and the second pilot's failure to restore the hydraulics.

The certificated flight instructor (CFI), who was seated in the left seat, reported that he was demonstrating practice hydraulic-off emergency procedures, as the second pilot, who was seated in the right seat, had an upcoming check ride where he would be required to conduct such maneuvers. While on the downwind leg of the traffic pattern, the CFI configured the helicopter to an airspeed of 60 knots (kts) with the hydraulics turned off. As he maneuvered the helicopter onto final approach, the cyclic became stiff, with increasing force required to manipulate it. The control forces on the cyclic were becoming increasing harder to overcome and difficult to move, while the collective remained in the neutral position. The CFI was trying to hold the cyclic in the forward right position and was using a large amount of physical force to do so. As the helicopter slowed it began to drift to the left of the intended approach site and the CFI attempted to move the cyclic to correct the drift, but could move the control due to the stiffness. He attempted to accelerate and instructed the second pilot to restore the hydraulics, knowing that only the collective for the right-seated pilot had the hydraulics switch. The second pilot never restored the hydraulics. Seconds later the helicopter climbed to about 20 feet above ground level (agl) and the CFI had no control. The helicopter rolled to the left and impacted terrain. A review of the flight manuals revealed that the pilots followed the proper procedures to perform a practice hydraulic-off emergency procedure and maintained the correct airspeeds. The second pilot stated that he never turned the hydraulics back on because he recalled a warning in training that doing so at such a low altitude could result in the pilot unintentionally over-controlling the cyclic and the helicopter crashing. Anecdotally the Safety Board is aware of other pilots that share the same belief; however, the Rotorcraft Flight Manual does not specifically address the issue. An examination of the wreckage disclosed that the left lateral hydraulic servo was rigged out of limits (0.106 inches), though the helicopter's manufacturer stated that the anomaly would not have a noticeable affect in the capabilities or handling of the helicopter. The servo accumulators were examined and tested. Upon disassembly of the longitudinal servo, investigators observed that the liner exhibited a bulging area about 1 inch from the end, similar to mushroomed deformation. The piston was removed from the liner revealing that about 1/2 of the Teflon white piston pad was displaced from the piston seal groove. The anomaly could not be definitively attributed to a preimpact condition. Additionally, in spite of extensive analysis by the manufacturer, the significance of the anomaly is not yet fully understood at this time.

HISTORY OF FLIGHT On July 13, 2007, at 1320 Pacific daylight time, a Eurocopter AS350 B3, N811HP, experienced an in-flight loss of control while performing a practice emergency maneuver with the hydraulic system off at the Paso Robles Municipal Airport, Paso Robles, California. California Highway Patrol (CHP) Air Operations was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 91. The certificated flight instructor (CFI), commercial pilot undergoing instruction (second pilot), and passenger were not injured; the helicopter sustained substantial damage. The local public-use instructional flight departed Paso Robles about 1300. Visual meteorological conditions prevailed, and a flight plan had not been filed. The National Transportation Safety Board investigator-in-charge (IIC) conducted several interviews with the CFI and second pilot, both immediately after the accident, and in the weeks following. The purpose of the flight was for the CFI to give training to the second pilot, who was positioned in the right seat; another CHP employee occupied the aft left seat. The second pilot requested to perform practice hydraulic-off emergency procedures, as he had an upcoming check ride where he would be required to conduct such maneuvers. Prior to departure, the pilots determined that the helicopter was about 90 pounds under the published maximum gross weight. With the helicopter being heavy, the CFI opted to perform the first hydraulics-off maneuver and demonstrate the correct procedures. After departure, the CFI adjoined the helicopter with the left downwind leg of the traffic pattern for runway 19, where he planned a touchdown on a dirt landing site adjacent to the runway surface. He configured the helicopter to an airspeed of 60 knots (kts) and instructed the second pilot to turn the hydraulics off [the right-seated pilot has the hydraulic cutoff switch on their respective collective]. While on the base leg, he noted that the controls felt as if they were "heavy" and he had to exert a stronger force to hold the collective up. As he maneuvered the helicopter onto final approach, the collective force required became neutral and the cyclic became stiff, with more force required to manipulate it. As the helicopter continued on final approach, the CFI noticed the control forces on the cyclic were becoming increasingly harder to overcome. He asked the second pilot to guard the collective while he repositioned his hand. He affirmed his grip on the cyclic and again took control of the collective. As the helicopter slowed, the cyclic control continued to become extremely stiff and difficult to move, while the collective remained in the neutral position. The CFI was trying, using a great amount of pressure, to hold the cyclic in the forward-right position. The helicopter slowed out of effective translational lift (ETL), configured about 15 kts and 1 foot above ground level (agl). The helicopter began to drift to the left of the intended approach site and the CFI attempted to move the cyclic in response to the drift, but could not correct due to the stiffness of the control. He attempted to accelerate through ETL and touchdown further down. The helicopter continued to drift to the left [about 5 to 6 feet] and began climbing. The CFI then instructed the second pilot to "give me hydraulics back," knowing that only the collective for the right-seated pilot had the hydraulics switch. Seconds later the helicopter climbed to about 20 feet agl and the CFI had no control. The helicopter rolled to the left and landed hard on the left skid; it came to rest on its right side. The CFI noted that the slowest airspeed the helicopter ever reached was a minimum of 8 kts. He added that he was not sure if the cyclic was immobile in any additional direction, aside from the forward-right position, as he did not move it into another direction to prevent possible further loss of control of the helicopter. The CFI estimated that he performs hydraulics-off simulated emergency procedures on a regular basis; he has never experienced any problems or difficulty controlling the helicopter. The second pilot stated that he never turned the hydraulics back on because he recalled that doing so at such a low altitude could result in the pilot unintentionally over-controlling the cyclic and the helicopter crashing. PILOT INFORMATION Certificated Flight Instructor [Left Seat] A review of the Federal Aviation Administration (FAA) airman records revealed that the instructor held a commercial pilot certificate with ratings for rotorcraft helicopters, instrument helicopters, and private privileges in single engine land airplanes. He also held a flight instructor certificate for helicopters. The pilot's most recent second-class medical certificate was issued in January 2007, with a limitation that he must wear corrective lenses. According to the pilot, at the time of the accident he had accumulated 10,400 hours of total flight time. He had amassed a total of 8,406 hours while employed with the CHP of which 2,887 hours were in the same make and model as the accident helicopter. In the previous year, the pilot had given about 50 hours of instruction. His last biannual flight review was completed on May 17, 2006, in a Eurocopter AS350 B3; he completed a semiannual evaluation with the operator on January 4, 2007. Second Pilot [Right Seat] A review of the FAA airman records revealed that the second pilot held an airline transport pilot certificate with a rating for multiengine land airplanes. His certificate also was endorsed for commercial privileges in single engine land airplanes, rotorcraft helicopters, and instrument helicopters. He held a flight instructor certificate for airplane ratings of single engine land, multiengine land, and instruments. The pilot's most recent first-class medical certificate was issued in January 2007, with a limitation that he must wear corrective lenses. According to the second pilot, at the time of the accident he had accumulated a total flight time of 9,056 hours. While employed with the CHP, he had amassed a total of 4,552 hours in both airplanes and helicopters. He had logged a total of 1,956 hours in the same make and model as the accident helicopter. His last biannual flight review was completed on May 18, 2006, in a Eurocopter AS350 B3. HELICOPTER INFORMATION The helicopter was a Eurocopter AS350B3, serial number 3404. It was manufactured in 2001 and had accrued a total time in service of 6,240 hours at the time of the accident. Review of the aircraft maintenance records disclosed that the last 100-hour inspection was completed 45 hours prior to the accident on May 30, 2007. The most recent annual inspection was completed 340 hours prior to the accident on February 7, 2007. The Turbomeca Arriel 2B engine, serial number 22179, had accumulated a total time in service of 5,758 hours. Both the annual and 100-hour inspections were accomplished on the dates noted for the airframe. Prior Maintenance Issues The second pilot stated that he had flown the accident helicopter the day prior to the accident. During the flight he noticed that the collective had a tendency to "creep up" and a lot of friction was needed to keep it in the correct position. No other maintenance anomalies were noted. System The Eurocopter AS350 B3 is equipped with a single hydraulic system, which provides hydraulic boost to the cyclic, collective, and tail rotor controls. The main rotor control system consists of a series of rigid rods interconnected by bell cranks and reversing levers. The respective control linkages interface with the swash plate through three hydraulic servo actuators, which are designed to exert the necessary control force. A mixing unit is located aft of the cockpit and utilized as an interface for the cyclic and collective pitch controls. The unit