Accident at Frisco, Colorado, 3 Jul 2015 (N390LG)

Accident narrative

On July 3, 2015, about 1339 mountain daylight time, an Airbus Helicopters AS350 B3e, registration N390LG, crashed into a parking lot shortly after lifting off from the Summit Medical Center Heliport in Frisco, Colorado. The helicopter, operated by Air Methods Corporation, was destroyed by impact forces and a postcrash fire. The pilot was fatally injured, and the two flight nurses onboard were seriously injured.

**The Flight**

The flight was conducted under 14 Code of Federal Regulations Part 135 on a company flight plan in visual meteorological conditions. The planned destination was Gypsum, Colorado, for a public relations activity.

The 64-year-old pilot held an airline transport pilot certificate with a rotorcraft helicopter rating. He had accumulated more than 13,200 hours of total flight time, including 5,231 hours in AS350 variants, with 1,228 hours in the AS350 B3 and 111 hours in the AS350 B3e.

At 0734, the pilot contacted the Air Methods operations control center to receive the flight release. During a routine morning briefing at 0841, he relayed no problems with the weather or the helicopter and no anticipated safety issues or hazards.

**The Accident Sequence**

Surveillance video of the helipad showed the pilot preflighting the helicopter beginning about 1331. The flight nurse in the right aft seat stated that the helicopter had a rough takeoff with some unusual pitch and began to make a counterclockwise turn that paused momentarily before the helicopter continued climbing and turning. The flight nurse recalled that after a 360-degree turn, the pilot appeared to attempt to gain some forward airspeed, but after a very brief forward flight, the helicopter violently began spinning counterclockwise. The flight lasted about 32 seconds.

Surveillance videos capturing the liftoff showed the helicopter yaw to the left and spin counterclockwise several times. A witness estimated that the helicopter reached an altitude of about 100 feet before it started to descend. The helicopter impacted a recreational vehicle and the parking lot 360 feet southwest of the helipad.

Video analysis showed the helicopter impacted the ground with small pitch and roll angles at an estimated vertical speed of 58 feet per second. After impact, the helicopter rolled onto its right side. Three seconds after impact, fuel was visible flowing from the wreckage, followed by the onset of a postcrash fire. The postcrash fire consumed or severely damaged most of the helicopter. The pilot and the flight nurse in the left aft seat sustained severe thermal injuries. The pilot succumbed to his injuries about 75 minutes after the accident.

**What the Investigation Found**

*Wreckage and Engines* The engine was found at the main wreckage site. Free turbine blade shedding was consistent with a free turbine overspeed, likely due to the sudden decoupling of the engine from the main transmission at ground impact while the engine was still running. The main rotor blades and Starflex showed no signatures consistent with abnormal operation before ground impact. Video evidence showed that the tail rotor drive system was likely providing power to the tail rotor when the helicopter was lifting off.

*Weather* The closest official weather station reported winds from 280 degrees at 19 knots with gusts to 24 knots. Video of the helipad windsock indicated wind from the left at 15 knots or less. The Board concluded that the wind conditions at the time of the accident would not have prevented the pilot from maintaining yaw control of the helicopter.

*Flight Controls and Hydraulic System* The AS350 B3e features a dual hydraulic system that provides redundancy to the main rotor flight controls. However, the tail rotor system has only a single-cylinder servo control powered by the lower hydraulic system. A yaw load compensator provides continuous hydraulic power assistance to the pedal controls in the event of a loss of pressure to the lower hydraulic system.

Operational procedures required the pilot to perform a preflight yaw servo hydraulic check to ensure the yaw load compensator was functional. The steps involved moving the yaw servo hydraulic switch to the "OFF" position (cutting hydraulic pressure to the tail rotor circuit), depressing an "ACCU TST" button to deplete the hydraulic pressure in the yaw load compensator accumulator, resetting the button, and restoring hydraulic pressure by moving the yaw servo hydraulic switch to the "ON" position.

The Board concluded that the pilot most likely did not return the yaw servo hydraulic switch to its correct "ON" position before takeoff. This resulted in a lack of hydraulic pressure to the tail rotor servo control and the yaw load compensator accumulator.

Without hydraulic boost, the pedal loads required to maintain heading increase significantly. Simulations indicated that with a 15-knot left crosswind, the required right pedal control load would be about 161 pounds. The Board concluded that a lack of hydraulic boost to the pedals, resulting in significantly increased pedal loads, was the most likely cause of the loss of tail rotor control, which led to the left yaw that occurred simultaneously with takeoff.

The yaw servo hydraulic switch was found in the forward "ON" position in the wreckage, but its internal position at impact could not be determined due to thermal damage. A dent on the directional control lateral push-pull tube was consistent with the right pedal in its fully forward position at ground impact. The Board noted the possibility that the pilot recognized the switch was in the "OFF" position and moved it to "ON" late in the flight, leaving insufficient time to allow recovery of the helicopter.

The Board concluded that despite the significantly increased pedal loads, the pilot continued the takeoff to climb the helicopter above nearby obstacles and gain forward airspeed to counter the left yaw rotation, but his efforts were unsuccessful. Furthermore, the Board concluded the design of Airbus Helicopters dual-hydraulic AS350-series helicopters did not account for the possibility of pilot error in configuring the tail rotor hydraulic circuit or assessing the functionality of the yaw load compensator.

*Alerting* The pilot would not have had any visual or aural indications of the total loss of hydraulic boost to the pedals. Four months before the accident, Airbus Helicopters issued a service bulletin to incorporate a light on the caution and warning panel that would flash if the yaw servo hydraulic switch was in the "OFF" position. Air Methods had not yet performed a risk assessment for this nonmandatory service bulletin and the light was not installed on the accident helicopter. The Board concluded that a salient alert for insufficient hydraulic pressure in the tail rotor hydraulic circuit could have cued the pilot to the incorrect configuration.

*Hover Check* Air Methods and Airbus Helicopters procedures stated that the helicopter should lift off to a hover as part of the takeoff procedures to verify controllability and check systems. Video evidence showed that a hover check was not performed. The Board concluded that if the pilot had performed a hover check, he would have identified the pedal control anomaly at an altitude that could have afforded a safe landing on the helipad.

*Crashworthiness* The Board concluded that the impact forces of this accident were survivable for the helicopter occupants. However, the helicopter was not equipped with, and was not required to have, a crash-resistant fuel system. The Board concluded that if the helicopter had been equipped with a crash-resistant fuel system, the potential for thermal injuries to the occupants would have been reduced or eliminated.

Additionally, the medical crewmember seats were certified to 1965 crashworthiness standards requiring a 4-G downward load factor, rather than the 1989 standards requiring a 20-G downward load factor. The Board concluded that the flight nurse in the left aft seat had likely been restrained in his seat and was likely ejected from the helicopter with his seat during the accident sequence.

*Recorders* The helicopter was voluntarily equipped with an Appareo Vision 1000 onboard image recorder. The device sustained extensive heat damage. Data could not be recovered because the recorder did not comply with the crash-resistance provisions of the FAA technical standard order for such systems.

**Probable Cause**

The National Transportation Safety Board determines that the probable cause of this accident was Airbus Helicopters’ dual-hydraulic AS350 B3e helicopter’s (1) preflight hydraulic check, which depleted hydraulic pressure in the tail rotor hydraulic circuit, and (2) lack of salient alerting to the pilot that hydraulic pressure was not restored before takeoff. Such alerting might have cued the pilot to his failure to reset the yaw servo hydraulic switch to its correct position during the preflight hydraulic check, which resulted in a lack of hydraulic boost to the pedal controls, high pedal forces, and a subsequent loss of control after takeoff. Contributing to the accident was the pilot’s failure to perform a hover check after liftoff, which would have alerted him to the pedal control anomaly at an altitude that could have allowed him to safely land the helicopter. Contributing to the severity of the injuries was the helicopter’s fuel system, which was not crash resistant and facilitated a fuel-fed postcrash fire.