History of Flight
On November 23, 2012, at about 1410 mountain standard time, an American Eurocopter Corporation AS350 B3 helicopter, N3984A, operated by Customs and Border Protection (CBP), was substantially damaged following a loss of control while maneuvering near Newfield, Arizona. The helicopter had departed Davis Monthan Air Force Base, Tucson, Arizona, about 1210 for a routine air patrol mission conducted as a Public Use flight. Visual meteorological conditions prevailed.
About one hour into the mission, the pilot was diverted to assist other Border Patrol Agents. Approximately 45 minutes later, the pilot departed the area and decided to take a lunch break. He landed in a confined area about 2 miles north of the U.S./Mexico border. CBP investigators noted that while the landing zone was suitable, the pilot could not recall the exact point of landing relative to potholes and cattle hoof prints in dried mud. No discernable skid markings or ground scarring were found due to the hard surface.
After landing, the pilot performed a stability check with the cyclic and lowered the collective to the full down position. With Nr at 100%, he added cyclic and collective friction without engaging the collective lock. While retrieving his lunch from a bag aft and right of his seat, he felt the nose of the helicopter become light on the skids with a slight pitch up. He placed his hands back on the controls and added full forward cyclic to correct. Within seconds, the aircraft began exhibiting vertical dynamic oscillations that resonated and worsened. The pilot then applied collective to lift off and regain stability. CBP investigators reported that it is conceivable that at least one ground resonance strap was in a pothole depression and not in contact with the ground when the nose pitched up.
After lifting off, the helicopter lurched forward and downward in an unusually nose-low attitude, causing the lower wire strike blade to contact the ground and establish a pivot point. The pilot made an aggressive aft cyclic movement with positive collective, resulting in the tail skid contacting the ground and pushing the vertical fin and tail rotor gearbox upward. The main rotor severed the tail rotor drive shaft forward of the gearbox. The tail section bounced upward, followed by an uncommanded left yaw. The helicopter spun left until the pilot reduced collective to arrest the spin. It touched down in a nose-up attitude with slight aft drift and settled on its skids. After exiting, the pilot observed that the aft section of the tail boom was severed and the tail rotor was missing.
Personnel Information
The pilot, age 32, held a commercial pilot certificate with rotorcraft-helicopter and instrument helicopter rating, and a second-class FAA medical certificate issued March 22, 2012. According to CBP data, he had accumulated 2,240 total flight hours, 1,900 hours as pilot-in-command, and 655 hours in the accident make and model. His flight times in the previous 30, 60, and 90 days were 58.5, 72.9, and 95.4 hours, respectively. In the AS350, those times were 40.2, 50.3, and 70.8 hours. He completed his annual proficiency evaluation on May 27, 2012.
Aircraft Information
The helicopter was an American Eurocopter Corporation AS350B3 2B1, serial number 7105, acquired by CBP in 2011. Its most recent Continuous Airworthiness inspection was on November 16, 2012, at an aircraft total time of 1,000 hours. At the time of the accident, it had accumulated 56 hours since that inspection, for a total airframe time of 1,056 hours. It was powered by a single Turbomeca model 2B1 turbo-shaft engine producing 543 shaft horsepower.
Meteorological Information
CBP personnel reported that about the time of the accident, the sky was clear with gusty winds from the southeast and a temperature of about 84°F (29°C). At 1354, about 16 minutes before the accident, the weather at Nogales International Airport (44 nm east-southeast) reported wind 080° at 12 knots, visibility 10 miles, clear sky, temperature 27°C, dew point -2°C, and altimeter 30.18 inHg.
Wreckage and Impact Information
A damage assessment by American Eurocopter on December 5, 2012, found damage to the tail cone, vertical fins, tail rotor drive train, tail rotor blades and pitch change spider assembly, the right landing gear spring bent upwards, and the lower wire strike component bent. The engine produced a grinding noise when rotated.
Medical and Pathological Information
The pilot sustained a minor injury. CBP reported that the pilot was sufficiently rested before the mishap, with no evidence of fatigue or human factor issues adversely affecting his performance. No adverse medical histories or acute ailments were discovered.
Tests and Research
The Appareo Vision 1000 cockpit camera was sent to the NTSB Laboratory for data recovery. However, the camera had been unplugged; the last recording was from September 22, 2012, about two months before the accident. The internal media card yielded no data from the accident flight. CBP noted that had the camera been operational, the data would have been critical to the investigation.
Additional Information
The Pilot's Handbook of Aeronautical Knowledge defines situational awareness as "accurate perception of operational and environmental factors that affect the airplane, pilot, and passengers during a specific period of time." The Rotorcraft Flying Handbook describes ground resonance as an aerodynamic phenomenon with fully-articulated rotor systems, developing when rotor blades move out of phase, causing rotor disc imbalance. This condition can cause a helicopter to self-destruct in seconds but requires ground contact.