History of Flight
On October 22, 2012, at 0602 central daylight time, an Agusta SPA AW139 helicopter, registration N385RH, collided with terrain following a loss of control while being repositioned at Houma-Terrebonne Airport (HUM), Houma, Louisiana. One pilot (co-pilot, pilot flying) suffered serious injury; the other pilot was not injured. The helicopter was substantially damaged. The flight was operated by ERA Helicopters LLC under 14 CFR Part 91 in visual meteorological conditions.
The accident crew performed a preflight and reviewed the maintenance logbook before moving the helicopter to the A-5 pad. After run-up and power checks, they lifted off, hovered laterally, and shut down. Shortly after, they were asked to move to another pad. They restarted, the left-seat pilot lifted off, hovered backward, and made a right pedal turn to hover taxi. While lining up over the pad and descending forward, the main wheels touched down. The pilot reported oscillations began, which intensified as he lowered the collective. Believing it was ground resonance, he increased collective to lift off. The oscillations continued. He moved rearward and left to avoid another helicopter, then initiated a left pedal turn. Oscillations became severe, knocking off headsets. The helicopter entered a spin and impacted the grass hard while moving laterally left. Both pilots exited unaided.
Witnesses heard an unusual noise described as a compressor stall, a "whop, whop, whop," or a pulsing/surging sound. They saw the helicopter rise to 20–70 feet above ground, spin violently left, then descend and impact in an upright attitude.
Personnel Information
The pilot-in-command held an airline transport pilot certificate with a helicopter rating and a type rating in Agusta AW139 helicopters. He had a first-class medical certificate issued February 29, 2012, with no limitations. Total flight time was 3,153 hours, with 257 hours in AW139s. He completed initial AW139 ground school on February 23, 2012, and an initial checkride on February 29, 2012; his most recent proficiency check was June 6, 2012.
The co-pilot (pilot flying) held an airline transport pilot certificate with multi-engine and helicopter ratings, commercial privileges for airplane single-engine land and sea, and a flight instructor certificate with multiple ratings. He held a type rating in Sikorsky S-61 helicopters. His first-class medical certificate was issued March 22, 2012, with near vision limitations. Total flight time was 7,340 hours, with 6,711 rotorcraft hours and 25 hours in AW139s. He completed initial AW139 ground school on February 1, 2012, and an initial checkride on March 17, 2012; his most recent proficiency check was August 5, 2012.
Aircraft Information
N385RH was an AgustaWestland AW139, serial number 410013, with a total time of 2,063.3 flight hours. It had a five-bladed fully articulated main rotor and a four-bladed fully articulated tail rotor, powered by two Pratt & Whitney Canada PT6C-67C turboshaft engines. It had a dual hydraulic flight control system and a Honeywell Primus Epic integrated avionics system with automatic flight control (AFCS).
On October 18, 2012, at 2,062.2 total hours, the "orange" and "white" main rotor pitch control links were adjusted. An operational check flight was conducted and signed off as satisfactory. The night before the accident, the "blue" main rotor damper (s/n 10568) was removed due to a leak and replaced with damper s/n 1602. An operational check flight noted a slight vibration and a blade with a "slight dip" in track, but no written record of an out-of-track discrepancy was made, and no track-and-balance was performed.
Meteorological Information
At 0555, the HUM AWOS reported: wind 070° at 3 knots, visibility 10 miles, clear sky, temperature 13°C, dewpoint 13°C, altimeter 30.07 inHg.
Flight Recorders
The helicopter was equipped with a Penny & Giles MPFR combination flight data recorder (FDR) and cockpit voice recorder (CVR). The CVR recorded 2 hours of audio with power interruptions. It captured a maintenance test flight, repositioning, and the accident flight. During the test flight, the crew discussed a blade track issue and told a mechanic one blade was "pretty good out of track." On the accident flight, the CVR recorded engine start, liftoff, and sounds of rattling increasing in intensity, followed by aural warnings (rotor low, rotor high, bank angle, tail too low) and ground impact at 0602:02.
A sound spectrum study examined low-frequency sounds from the main rotor. At 100% Nr, the rotor generated 24.7 Hz; at 102% Nr, 25.2 Hz. Analysis of the test flight recording showed peaks near 25.2 Hz. The accident flight recording showed a peak at about 24.7 Hz initially, then peaks below 25 Hz.
The FDR contained about 25 hours of data, including the 3-minute accident flight. It showed no unusual indications until immediately before the weight-on-wheels switch activated, when a vertical oscillation began and gradually increased. Lateral and longitudinal accelerations also occurred but were less severe.
Tests and Research
From October 23–26, 2012, the FAA, ERA Helicopters, and AgustaWestland examined the helicopter at HUM. The helicopter was later moved to Heli-Works in Pensacola, Florida, where additional examinations occurred on December 5, 2012.
Flight control continuity was confirmed from both pilots' cyclic and collective sticks to the main rotor hydraulic actuators. No hydraulic leaks were found; operational checks of all hydraulic systems revealed no anomalies. Main rotor servo actuators were secure with no binding. Floor structure damage near the nose landing gear restricted cyclic movement, but after clearing, cyclic moved freely with no binding. Trim checks were normal.
Main gearbox attachment points, anti-torque beam, and chip detectors showed no anomalies. Main, intermediate, and tail gearbox oil levels were correct. Swashplate duplex bearing and stationary swashplate/scissors showed no excessive play. Main rotor servo actuator connections and head retaining bolts met torque requirements.
Main rotor dampers were sent to Mecaer Aviation Group in Italy for bench testing. The 'blue' damper (s/n 1602) had hub-side spherical bearing friction beyond allowable limits. The 'red' damper (s/n 1660B) and 'white' damper (s/n 1724B) had out-of-tolerance response curves (tensile and compressive, respectively) attributed to a worn valve seat. The remaining three dampers met specifications. These checks are not field inspections.
Pitch control links were examined. The lower rod end of the 'orange' link rotated about 30° (lockwire intact). Upper rod end spherical bearings showed axial play: 'blue' 0.30 mm, 'black' 0.25 mm, 'white' 0.25 mm (with about 10° rotation, lockwire intact). Maximum allowed play is 0.20 mm. No other anomalies were found.
Main rotor blade tension links were undamaged. Elastomeric bearings were sent to Paulstra in France; no cracks were found. Blade flap limiters showed impact marks: 'red' heavy, 'black' and 'white' moderate, 'orange' and 'blue' none.
Five main rotor blades were intact with no surface damage. At Bell Helicopter Broussard, tap testing showed no delamination. Static balance weights showed minor changes; the 'white' blade had a larger weight change, but x-ray found no water or anomalies. The reason for the weight change could not be determined.
Examination of the airframe at frame stations 3900 and 5700: STA 3900 undamaged; right side of STA 5700 had impact damage; left side undamaged.
Two modular avionics units (MAU) from the AFCS were bench tested at Honeywell. All four MAUs were in good condition, with no pre-existing conditions preventing proper operation.
Probable Cause
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