History of Flight
On June 7, 2013, about 2140 central daylight time, a Eurocopter AS 350 B3 helicopter, registration N106LN, impacted terrain and came to rest on its side at Grand Prairie Municipal Airport (GPM), near Grand Prairie, Texas. The two pilots sustained minor injuries. The helicopter sustained substantial tailboom damage. The helicopter was registered to CFS AIR LLC, Danbury, Connecticut, and operated by Air Methods Corporation, Englewood, Colorado, under 14 Code of Federal Regulations Part 91 as an instructional flight. Night visual flight rules (VFR) conditions prevailed; the flight did not operate on a VFR flight plan. The local flight originated from GPM about 2111.
According to the instructor pilot, they were performing a simulated hydraulics failure maneuver. On shallow approach, he instructed the pilot under instruction to fly to a designated point for a go-around. As the pilot descended to approximately 3-5 feet, the instructor mentioned a go-around again. When the pilot increased power, the nose came up, and the instructor told him to lower the nose to increase airspeed. The pilot reported difficulty applying right pedal. The instructor came on the controls to assist as the aircraft began turning left of runway heading. The instructor applied forward cyclic, possibly overcompensating, and the nose pitched down. The instructor perceived the pilot applying aft cyclic. The aircraft began spinning left with extreme pitch changes and not climbing. The instructor stated he may have told the pilot to turn the hydraulic switch back on. The aircraft entered a water retention basin, heading toward an RV park. The instructor reduced power to slow rotation, then applied power to cushion the impact. The helicopter impacted the ground and rolled onto its right side.
The pilot under instruction reported that after departure from runway 35, they entered left closed traffic. The check airman initiated simulated hydraulics off by depressing the hydraulic test switch. The pilot slowed to 60 knots and moved the hydraulic switch to off. On final approach for a low approach, the check airman requested a go-around. When the pilot applied power and lowered the nose, the helicopter yawed about 45 degrees left and the nose tucked slightly. Right pedal input was unable to correct the yaw. As they moved left of the runway, right cyclic caused a crab but the nose continued left. At about 90 degrees to the runway, the check airman took control as the helicopter began a rapid series of left turns, each faster and more violent, until impacting sloping terrain west of the runway. The aircraft landed left skid high on the slope and rolled onto its right side facing southeast.
Personnel Information
The instructor pilot, age 64, held a commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings, and a flight instructor certificate with helicopter and instrument helicopter ratings. He held a second-class medical certificate issued October 17, 2012. He accumulated 10,550 total flight hours, including 1,851 hours in AS350 helicopters. In the 90 days before the accident, he flew about 75 hours; 32 hours in the last 30 days; and 4 hours in the last 24 hours. His most recent flight review was January 14, 2013. Additional flight time since April 2008 included AS350 B (5+00), BA (10+26), B2 (282+10), and B3 (205+05) hours.
The pilot under instruction, age 66, held a commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings. He held a second-class medical certificate issued November 21, 2012. He accumulated 9,511 total flight hours, including 76 hours in AS350 helicopters. In the 90 days before the accident, he flew about 18 hours; 1 hour in the last 30 days; and 1 hour in the last 24 hours. His most recent flight review was June 8, 2012. Additional flight time since April 2008 included AS350 B2 (2+25) and B3 (119+31) hours.
Aircraft Information
N106LN was a 1999 model Eurocopter AS 350 B3, serial number 3251. It had a replacement FAA airworthiness certificate issued March 28, 2000. The most recent maintenance inspection was completed June 6, 2013, with 7,682 total hours. Maximum gross weight was 4,961 pounds. The engine was a Turbomeca Arriel 2B, serial number 22036, rated at 747 horsepower for takeoff and 728 horsepower for continuous operations. At the time of the accident, weight and balance were within limits at 4,355 pounds and a moment arm of 135.9 inches.
On November 2, 2004, N106LN experienced a partial power loss after takeoff and hard landing, substantially damaging the tailboom. A major repair and alteration form approved its repair on April 1, 2005.
Meteorological Information
At 2135, weather at GPM was: wind 040 degrees at 4 knots; visibility 10 statute miles; sky clear; temperature 24°C; dew point 11°C; altimeter 29.93 inches of mercury.
Wreckage and Impact Information
The helicopter came to rest on its right side in the grass infield west of runway 35, about 1,000 feet from the runway threshold. Main rotor blades exhibited varying damage consistent with terrain impact. The cowling over the rotor mast was deformed and torn. The left side fuselage and tailboom near their juncture showed buckling. A semicircular opening was torn in the cowling covering the tail rotor driveshaft about a foot aft of the tailpipe exhaust heat shield. Skid-width indentations were noted in the grass.
FAA representatives and technical advisers examined the wreckage. The engine and main rotor gearbox remained attached. Flight control continuity was traced; all separations were consistent with overload. The hydraulic system was pressurized with no leaks; all servos, accumulators, and the tail rotor servo and yaw load compensator functioned when tested.
Additional Information
The FAA Helicopter Flying Handbook describes effective translational lift (ETL) between 16 and 24 knots, where the rotor system works in undisturbed air, reducing induced flow and drag.
The Eurocopter AS 350 B3 Flight Manual Supplement for Hydraulic Pressure Failure Training describes simulating loss of hydraulic power by depressing the HYD TEST pushbutton. The simulation causes the same effects as a real failure except the tail rotor load compensator is depressurized, increasing right pedal forces. The manual cautions against hover or low-speed maneuvers without hydraulic pressure and notes that the hydraulic failure safety speed is 40 to 60 knots.
Flight Recorders
The helicopter was equipped with a vehicle engine multifunction display (VEMD) and a digital engine control unit (DECU). VEMD data showed the accident flight was about 20 minutes long. Three failures and two overlimits events were recorded near the end: a collective pitch potentiometer failure consistent with main rotor blade ground impact, followed by fuel gage failures consistent with fuel migration during rollover. No pre-impact failures or overlimits were recorded.
DECU data showed first faults at 24 minutes 12 seconds after power up: a collective pitch measurement exceeding software parameters. Subsequent faults at 24 minutes 52 seconds included raw torque and collective pitch exceedances. A real-time check showed the DECU operating normally.
Medical and Pathological Information
The pilot under instruction provided a toxicology sample; results were negative. The instructor pilot was hospitalized, precluding testing.
Organizational and Management Information
Air Methods Corporation, a commercial on-demand air taxi operator specializing in helicopter emergency medical services, operates under 14 CFR Part 135. The company's Pilot Training Program includes recurrent training with ground and flight hours. Training flights typically last 1-1.5 hours; check flights about 1 hour. Air Methods uses dedicated training helicopters and simulation devices.