CEN13FA025

The helicopter’s sudden and severe vertical vibrations during landing, which resulted in a collision with terrain. The reason for the helicopter’s sudden and severe vertical vibrations could not be determined during postaccident examinations.

The flight crew was repositioning the helicopter to another landing pad when the accident occurred. According to the flight crew and flight data recorder (FDR) data, as the helicopter was touching down, it began to experience severe vertical vibrations and to oscillate violently. The pilot reported that he lowered the collective but that the vibrations and oscillations intensified. The pilot then increased the collective to lift the helicopter off the ground. The helicopter became airborne, but the violent oscillations and vibrations continued. The pilot initiated a left pedal turn to avoid another helicopter, at which time, the oscillations and vibrations were so severe that the pilots' headsets came off of their heads. The helicopter entered a spin and impacted the grass hard while moving laterally to the left. The pilots shut down and then exited the helicopter. The blue main rotor blade damper was replaced the night before the accident. A maintenance test flight was performed following the replacement. The flight crewmembers who flew the test flight reported that there was a slight vibration from the main rotor system and that one of the five main rotor blades had a "slight dip" in its track. There was no record of the main rotor blade out-of-track discrepancy nor of a main rotor track and balance inspection being performed subsequent to this flight. Although an out-of-track blade could cause a persistent vertical vibration, an examination of the main rotor blades, elastomeric bearings, main rotor dampers, main rotor rod ends, main gearbox attachment points and antitorque beam, and automatic flight control system did not reveal any anomalies that could account for the vertical vibrations reported by the flight crew and recorded on the FDR.

HISTORY OF FLIGHT On October 22, 2012, at 0602 central daylight time, an Agusta SPA AW139 helicopter, N385RH, collided with the terrain following a loss of control while the helicopter was being repositioned on the Houma-Terrebonne Airport (HUM), Houma, Louisiana. One of the airline transport rated pilots was not injured and the other suffered a serious injury. The helicopter was substantially damaged. The helicopter was registered to and operated by ERA Helicopters LLC, and was being operated under the provisions of 14 Code of Federal Regulations Part 91 at the time of the accident. Visual meteorological conditions prevailed. The accident flight crew reported they performed an aircraft preflight and reviewed the maintenance logbook prior to moving the helicopter outside to the A-5 pad. They completed the run-up and power/trend checks after which they lifted the helicopter off the ground and hovered laterally to center the helicopter on the pad. They then shut down the helicopter. Shortly after shutting down the helicopter, they were asked to move the helicopter to another pad. They started the helicopter once again, and the left seat pilot lifted the helicopter, hovered backwards, and made a right pedal turn to hover taxi to the pad. The pilot lined the helicopter up over the edge of the pad and began a descent while moving forward. He lowered the helicopter and the main wheels touched down. He stated he was not sure if the nose wheel had fully touched down, but the helicopter began to "oscillate violently." The pilot stated he continued to lower the collective, but the vibrations and oscillations intensified. Initially thinking that they had encountered ground resonance, the pilot increased the collective to lift the helicopter off the ground. The helicopter became airborne, and the violent oscillation and vibration continued. The pilot stated he was able to move the helicopter rearward and to the left away from another helicopter that was being fueled. He initiated a left pedal turn at which time the oscillations and vibrations were so severe that the pilots' headsets came off of their heads. The helicopter entered a spin and impacted the grass hard while moving laterally to the left. The pilots shut down the helicopter and both were able to exit the helicopter on their own. Numerous witnesses saw and heard the helicopter during the accident sequence. The witnesses described hearing an unusual noise that was described as "a compressor stall", a "whop, whop, whop", and a pulsing/surging sound. The witnesses stated the helicopter rose to an altitude between 20 and 70 feet above the ground and spun violently to the left. They stated the helicopter then descended and impacted the ground in an upright attitude. PERSONNEL INFORMATION The pilot-in-command held an airline transport pilot certificate with a helicopter rating. The pilot-in-command was type rated in Agusta AW139 helicopters. He was issued a first class airman medical certificate with no limitations on February 29, 2012. According to ERA the pilot had a total flight time of 3,153 hours of which 257 hours were in Agusta AW139 helicopters. The pilot-in-command completed his initial AW139 ground school training with ERA Helicopters on February 23, 2012. He completed his initial AW139 checkride with ERA Helicopters on February 29, 2012, and his most recent proficiency check was on June 6, 2012. The co-pilot, who was the pilot flying when the accident occurred, held an airline transport pilot certificate with multi-engine and helicopter ratings and commercial privileges for airplane single-engine land and airplane single-engine sea. a commercial pilot certificate with single-engine land and single-engine sea airplane ratings. He held a flight instructor certificate with a single-engine land, multi-engine land, helicopter, and instrument ratings. The pilot held a type rating in Sikorsky S-61 helicopters. He was issued a first class airman medical certificate with near vision limitations on March 22, 2012. According to ERA Helicopters, the pilot had a total flight time of 7,340 hours. He had a total rotorcraft time of 6,711 hours of which 25 hours were in Agusta AW139 helicopters. The co-pilot completed his initial AW139 ground school training with ERA Helicopters on February 1, 2012. He completed his initial AW139 checkride with ERA Helicopters on March 17, 2012, and his most recent proficiency check was on August 5, 2012. AIRCRAFT INFORMATION N385RH was an AgustaWestland AW139, serial number (s/n) 410013. The helicopter had a total time of 2,063.3 flight hours at the time of the accident. The helicopter had a five-bladed, fully articulated main rotor system that provides lift and thrust, and a four-bladed, fully articulated tail rotor system that provides main rotor anti-torque and directional control. The helicopter was equipped with two Pratt & Whitney Canada PT6C-67C turboshaft engines. The helicopter had a dual hydraulic flight control system and the Honeywell Primus Epic integrated avionics system that contained an automatic flight control system (AFCS). On October 18, 2012, at a helicopter total time of 2,062.2 hours, the "orange" and "white" main rotor pitch control links were adjusted. An operational check flight was conducted and the flight was signed off as being "complete and satisfactory." On the night prior to the accident, the helicopter underwent maintenance during which "blue" main rotor damper, s/n 10568 was removed due to a reported leak. Damper s/n 1602 was installed in the "blue" main rotor blade position. An operational check flight was conducted following the maintenance. The crew from this flight stated there was a slight vibration from the main rotor. They returned to the maintenance base where they landed and shut down the helicopter. They stated that they were able to see that one of the blades had a "slight dip" in its track which they attributed to have been the cause of the vibration. They stated they informed maintenance personnel that the flight was satisfactory, and of the slight vibration and blade dip. The crew stated the helicopter was then towed into the hangar. There was no written record of the crew reporting a main rotor blade out-of track discrepancy, nor was there a main rotor track and balance performed subsequent to the operational check flight. METEOROLOGICAL INFORMATION At 0555, the HUM airport Automated Weather Observing System (AWOS) recorded the weather conditions as: wind 070 degrees at 3 knots; visibility 10 miles; clear sky; temperature 13 degrees Celsius; dewpoint 13 degrees Celsius; and altimeter 30.07 inches of mercury. FLIGHT RECORDERS Cockpit Voice Recorder (CVR) The helicopter was equipped with a Penny & Giles MPFR combination flight data recorder and CVR. The solid state CVR recorded 2 hours of digital cockpit audio. The CVR was removed from the helicopter and sent to the NTSB Recorders Laboratory for the audio information to be extracted. The 2-hour recording contained several power interruptions, causing discontinuity in the time scale. As such, multiple correlations with the flight data recorder (FDR) were accomplished. The recording did contain a period of mechanics working on the helicopter, a maintenance test flight, movement of the helicopter out of the hangar, a repositioning flight, and the accident flight. A partial transcript of the maintenance test flight was developed from the recording. The recording began at 0023:33 and ended at 0048:15. During the flight, the crew discussed the blade tracking issue stating it the helicopter had a "hop" to it and that they could "see it in the blades." The crew stated it looked like a track problem and they speculated that someone probably bumped trim tab. After landing, the crew was heard having a discussion with a mechanic. The crew informed the mechanic that there was one blade that was "pretty good out of track." Th