Fort Worth, TX, USA
N747CH
EUROCOPTER AS 350 B2
The pilot had recently purchased the helicopter and was receiving flight training from a certified flight instructor (CFI). During practice traffic pattern work, the helicopter’s hydraulic system was turned off to simulate hydraulic failure on the flight control system. During the approach, the airport’s ground controller reported that they were on the wrong radio frequency, so the CFI changed the radio to the correct frequency. The helicopter’s airspeed slowed and the helicopter entered an uncommanded left yaw. The CFI tried to regain control by adding right pedal, trying to gain for forward airspeed, and reducing power. The helicopter did not respond to the CFI’s control inputs. Subsequently, the helicopter impacted the ground, rolled on to its side, and a postcrash fire ensued. A postaccident examination of the helicopter revealed no preimpact mechanical malfunctions or failures that would have precluded normal operations. A review of the helicopter’s flight manual reveals the note: “Caution, Do not attempt to carry out hover flight or any low speed maneuver without hydraulic pressure assistance. The intensity and direction of the control feedback forces will change rapidly. This will result in excessive pilot workload, poor aircraft control, and possible loss of control." Additionally, one or both pilots may have been distracted by the incorrect radio frequency.
HISTORY OF FLIGHT On May 29, 2011, about 1145 central daylight time, a Eurocopter AS 350 B2 helicopter, N747CH, impacted terrain while on approach to the Fort Worth Alliance Airport (AFW), Fort Worth, Texas. The private rated pilot, flight instructor, and passenger received minor injuries. The helicopter was substantially damaged during the accident and a postcrash fire ensued. The aircraft was registered to and operated by a Sovereign International Equities, LLC, Portland, Oregon under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The pilot had recently purchased the helicopter. The certified flight instructor (CFI), who was employed by the helicopter’s previous owner, was to help ferry the helicopter from Puerto Rico to Texas, and then provide the new owners with flight instruction in the helicopter. The CFI reported that he was giving the pilot instruction with normal and emergencies procedures in the helicopter. During the last traffic pattern, the hydraulic system was turned off, to simulate a hydraulic system failure. The CFI added that the ground controller reported that they were on the wrong radio frequency, so he moved to correct the radio frequency. During the approach, the helicopter slowed and started a left yaw. The CFI stated that he tried to regain control by adding right pedal, looking for forward airspeed, and reducing power. The helicopter did not respond to the CFI control inputs, descended and impacted terrain. PERSONNEL INFORMATION The CFI held commercial pilot and flight instructor certificates for rotorcraft-helicopter, and a private pilot certificate for airplane single-engine land. His last first-class Federal Aviation Administration (FAA) medical was issued on May 28, 2010. The CFI reportedly had approximately 3,466 total flight hours, and about 789 hours in a Eurocopter AS 350. The pilot sitting in the right seat held a private pilot rotorcraft-helicopter rating. His FAA third-class medical was issued on August 23, 2010. The pilot’s logbook was not located during the course of the investigation; however, he estimated his total flight time at 4,200 hours, with about 9 hours in the accident helicopter. The rear seat passenger also held private pilot certificates for airplane, single-engine land and rotorcraft-helicopter ratings. AIRCRAFT INFORMATION The accident helicopter was 2004 Eurocopter AS350B2, “A-star”, which is a single-engine helicopter powered by a Turbomeca Arriel turboshaft engine. The helicopter had just been purchased from Caribbean Heli-Jets, Puerto Rico, by the LLC. Under the previous owner, the helicopter was maintained in accordance with the manufacturer’s recommended maintenance plan, and had accumulated approximately 2,168 hours. METEOROLOGICAL INFORMATION The automated weather station at KAFW, reported at 1145, wind at from 160 degrees at 20 knots gusting to 27 knots, temperature 86 degrees Fahrenheit, dew point 68 degrees Fahrenheit, visibility 10 miles, a clear sky, and an altimeter pressure setting 29.76 inches of Mercury. COMMUNICATIONS The pilot’s were in contact with the AFW tower controller. During the airborne traffic pattern work, the private pilot inadvertently contacted ground control; the ground controller advised them that they were on the wrong frequency. Otherwise, communication between AFW tower and the accident helicopter were routine, additionally, no emergency or distress calls were received. RADAR INFORMATION The Alliance approach radar did not display the accident helicopter during its traffic pattern work, or during the accident sequence. AIRPORT INFORMATION Fort Worth Alliance Airport (AFW) is a public use airport, located about 14 miles north of Fort Worth, Texas. The airport has class D airspace with a continuous operated control tower. The airport features two parallel concrete runways. Runway 16L-34R is 9,600-foot long and 150 foot wide. Runway 16R-34L is 8,220 foot and 150 foot wide. The field elevation is 722 feet mean sea level (msl). The airport is located about 16 miles northwest of the Dallas-Fort Worth International airport (DFW), and underneath DFW’s class B airspace. WRECKAGE AND IMPACT INFORMATION Inspectors from Federal Aviation Administration (FAA) examined the helicopter wreckage on-site. All major components of the airplane were accounted for at the scene. The main wreckage came to rest on its right side. The right side skids were torn from the fuselage, the tailboom horizontal stabilizers were damaged, the main rotor blades remained attached to their respective hubs, but exhibited severe impact and heat damage; one of the two tail rotor paddles (blades) separated on impact. A post crash fire partially consumed the cabin area. TEST AND RESEARCH The National Transportation Safety Board Investigator-In-Charge (IIC), inspectors FAA, and technical representatives from the airframe and engine manufacturers examined the helicopter wreckage, after recovery, at a salvage yard. Examination of the helicopter did not reveal any preimpact mechanical malfunctions. The helicopter’s 30 alpha switch central console and caution warning panel were sent to the NTSB Materials Laboratory in Washington, D.C., for further examination. Both units received heavy thermal damage by the postcrash fire. The Materials Laboratory examination revealed some evidence of filament sagging on several of the bulbs, most likely due to age. There were no broken filaments and there was no evidence of hot filament stretching found on any of the filaments of the examined bulbs. Additionally, the position of the push-type buttons on the systems control panel could not be determined, due to the unit’s fire damage. ADDITIONAL INFORMATION According to the Eurocopter AS 350 B2 Flight Manual (Emergency Procedures) and Flight Manual Supplement, Hydraulic Pressure Failure Training Procedures: To simulate a loss of hydraulic power, depressing the “HYD TEST” pushbutton on the central console produces the same effects as a real failure: The hydraulic pump pressure is by-passed The main rotor accumulators give limited time hydraulic assistance back-up. The red HYD Light comes on, the horn sounds. The simulation of a hydraulic failure is the same as a real failure with the exception that the main rotor load compensator is depressurized and tail rotor pedal control feedback forces are higher than normal when pushing on the right pedal. Note: The instructor must ensure that the “HYD TEST” pushbutton on center console is selected OFF (upper position) before the collective hydraulic cut-off switch is selected OFF to ensure that the tail rotor compensator is pressurized, and to enable the pilot to restore the hydraulic power system by re-setting the hydraulic cut-off switch to ON during the training exercise should it become necessary. The manual also notes that the hydraulic failure safety speed is 40 to 60 knots. The manual also states: “Caution: Do not attempt to carry out hover flight or any low speed maneuver without hydraulic pressure assistance. The intensity and direction of the control feedback forces will change rapidly. This will result in excessive pilot workload, poor aircraft control, and possible loss of control."
The pilot’s loss of control due to his not maintaining adequate airspeed and altitude during a simulated hydraulic flight control failure. Contributing to the accident was the flight instructor’s inadequate supervision and delayed remedial response.
Source: NTSB Aviation Accident Database
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