History of Flight
On January 10, 2014, about 0815 central standard time, a Eurocopter AS350B3 helicopter, registration N3948A, impacted trees and terrain after a loss of control near Encino, Texas. The pilot sustained serious injuries, and two crew members sustained minor injuries. The helicopter sustained substantial damage. The helicopter was registered and operated by the United States Customs and Border Protection (CBP), Washington, DC, under 14 Code of Federal Regulations Part 91 as a public use flight. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from McAllen International Airport (KMFE), McAllen, Texas, about 0610.
According to the pilot, the crew was conducting a law enforcement patrol flight to assist other CBP agents on the ground near Encino. The pilot flew the helicopter in a left orbit at 800 feet above ground level (AGL), eventually descending to 150 feet AGL and hovering on a southerly heading. The helicopter began to drift southeast, so the pilot repositioned with a left climbing turn. During the turn, he reported feeling the wind catch the tail and a slight shimmy before the helicopter spun rapidly to the left. He applied full right pedal and attempted to accelerate, believing he regained control. However, the helicopter continued the left spin and impacted trees and terrain. Prior to impact, the pilot heard a sound he recognized as the low rotor RPM horn. He reported no preaccident mechanical malfunctions or failures.
The two crew members stated the wind was strong and gusting during the flight, significantly stronger at higher altitudes. The pilot expressed concern about the wind while maneuvering. While maneuvering in a left-turn pattern about 50–125 feet AGL, the pilot felt the helicopter shudder, followed by a quick left rotation and descent. They reported the helicopter seemed to be operating normally before the accident. One crew member secured the fuel cutoff, activated the rotor brake, and turned off the electrical master switch after impact, noticing smoke from the engine compartment.
A witness observed the helicopter 50–100 feet above the ground and about 25 feet above the treetops, then an abrupt maneuver and descent into the trees. The helicopter came to rest on its right side.
Personnel Information
The pilot, age 28, held a commercial pilot certificate for airplane single-engine land, multiengine land, and helicopter, with instrument ratings for airplane and helicopter. He was a certified flight instructor for airplane single-engine land and multiengine land. He held a first-class medical certificate issued October 23, 2013, with no limitations. He had accumulated 111 hours in the helicopter make and model, with 100 hours as pilot-in-command. His training records indicated no additional formal mission training from the local branch; he received informal on-the-job training and completed 15 hours of enforcement mission time in a helicopter prior to assignment. Before the accident flight, he had two scheduled days off.
The second flight crew member was a supplemental air crew member seated in the left front seat, not manipulating the controls. The third crew member was an air crew rifle operator seated in the left rear seat.
Aircraft Information
The six-seat, single-engine helicopter, serial number 4948, was manufactured in 2010. It was powered by a 747-shaft horsepower Turbomeca Arriel 2B1 turboshaft engine. The airframe and engine both had a total time of 1,397 hours at the time of the accident. The most recent 100-hour inspection was completed December 13, 2013, at 1,378.8 hours, and the most recent 600-hour inspection on October 8, 2013, at 1,180 hours.
Meteorological Information
At 0815, the automated weather report for Brooks County Airport (KBKS), 10 miles north of the accident, reported wind from 160 degrees at 10 knots gusting to 14 knots, visibility 10 miles, scattered clouds at 3,600 feet, temperature 19°C, dew point 17°C, and altimeter setting 29.89 inches of mercury. The flight crew estimated the wind at the accident site to be about 15 knots, gusting to 20 knots, and noted stronger winds at higher altitudes.
Wreckage and Impact Information
The wreckage was located on a ranch about 50 miles north of McAllen. The fuselage came to rest on its right side, oriented at a magnetic heading of approximately 290 degrees. Debris was localized near the main wreckage. A postimpact fire was extinguished by first responders. The cabin structure was mostly intact, with forward windows broken and the left rear door separated. The forward nose, underside fuselage, and right skids were driven into the sand. The tail boom was bent at the aft flex-coupling of the forward steel drive shaft.
The transmission and main rotor system remained attached to the transmission deck, with all transmission support arms broken. The Starflex had two arms broken mid-span (red and yellow), and one arm separated from its thrust bearing. Main rotor blades showed leading edge ground impact damage. The tail-rotor gear box remained attached; one blade was damaged and separated mid-span with wood debris, the other less damaged. The tail rotor rotated freely, and the chip plug was clean. The fuel tank was undamaged, with no leaks. The cockpit fuel cutoff and rotor brake handles were in the OFF position. The right horizontal stabilizer exhibited impact signatures and a tree strike.
Flight control continuity was established from the pilot's cyclic and collective to the rotor system. The anti-torque pedals were in the full right forward position and could not be moved due to impact damage. The collective was up, and the throttle was at idle. All circuit breakers were in. The instrument panel was relatively intact. Thermal damage was evident on the left and top sides of the engine cowling, consistent with a postimpact fire. The transmission shaft coupling ruptured; the gas generator could not be rotated manually. Free turbine blades were shed, with some found below the helicopter. Reduction gearbox output pinion nut alignment marks were misaligned about 1.5 mm, consistent with power delivery during blade strikes. Data from the Digital Engine Control Unit (DECU) and Vehicle Engine Monitoring Display (VEMD) showed failures and over limits within seconds corresponding to impact, with no preimpact failures indicated.
Additional Information
FAA Advisory Circular 90-95, Unanticipated Right Yaw in Helicopters, states that loss of tail rotor effectiveness (LTE) is a critical, low-speed aerodynamic characteristic that can result in an uncommanded rapid yaw rate. It may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots. Conditions include high-power, low-airspeed environments with left crosswinds or tailwinds. The AC advises avoiding tailwinds, out-of-ground-effect hover, and high power demand situations; being aware of wind direction and velocity; and monitoring pedal position and changing conditions.