N805AR

HISTORY OF FLIGHTOn September 6, 2016, about 1340 eastern daylight time, a Sikorsky S-61N, N805AR, was destroyed when it impacted a field after experiencing a dual loss of engine power while in a hover near Palm Bay, Florida. The airline transport pilot, the commercial-rated copilot, and the maintenance crewmember were fatally injured. The helicopter was registered to EP Aviation LLC and was being operated by AAR Airlift Group under the provisions of Title 14 Code of Federal Regulations Part 91 as a post-maintenance flight. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed for the local flight that departed Melbourne International Airport (MLB), Melbourne, Florida, at 1324.

According to the operator, the helicopter's fore/aft pitch servo had recently been removed and replaced. Subsequently, three functional check flights (FCF) were required to be completed. Two FCFs were completed uneventfully the day of the accident, and the crewmembers were conducting the final FCF when the accident occurred. One of the maneuvers to be performed during the final FCF was rearward flight at a computed airspeed of 20 knots. According to the cockpit voice recorder (CVR), the flight crew performed two of these rearward FCF maneuvers during the accident flight.

Video taken by a ground witness recorded the helicopter performing the first rearward maneuver about 200 ft above ground level. Correlation of the video to the CVR showed the helicopter flying rearward at 1337:25, when the copilot stated the rear speed was 15 knots. At 1337:40, the helicopter continued to fly rearward as the copilot stated the rear speed was 20 knots. Two thumping sounds were recorded on the CVR at 1337:42 and 1337:44, when the rear speed was about 31 knots, but corresponding sounds could not be identified in the ground witness video. The ground witness video then showed the nose of the helicopter pitch down as the helicopter transitioned from rearward flight to a forward left 90° turn and continued forward in straight and level flight. During the recovery maneuver, an event occurs which caused a 2-second region of overdriven audio to be recorded on the CVR. This occurred during the left pedal turn and while the helicopter was approaching 90° to the rearward flightpath. The helicopter then flew an orbit in increasing altitude, and the video ended.

According to the CVR, the pilot took over control of the helicopter at 1336:41 and the copilot, who was receiving flight training on the day of the accident, identified the thumping sounds as a compressor stall, and the pilot agreed. The pilot then told the maintenance crewmember that they were returning to MLB. At 1338:02, the flight crew discussed the perceived compressor stall and engine exhaust gas temperatures. Then at 1338:26, the pilot told the maintenance crewmember that they were going to try the maneuver again in a different direction relative to the wind (with the wind off the nose), and the maintenance crewmember stated that it was okay with him. At 1339:46, the pilot was recovering from flying rearward when there was a change in background noise, which the maintenance crewmember identified as a compressor stall. The audio for the cockpit area microphone was overdriven again from about 1339:45 to 1339:48. At 1339:48, the copilot stated that the "AFCS is back on" while there was another change in background noise consistent with a decay in drivetrain rpm. The recording ended at 1339:55.

There were no known witnesses to the impact. PERSONNEL INFORMATIONThe pilot in the left seat held an airline transport pilot certificate with a rating for rotorcraft helicopter and commercial privileges in airplane single- and multi-engine land and instrument airplane. In addition, the pilot held a flight instructor certificate with ratings for rotorcraft helicopter and instrument rotorcraft. The pilot's most recent Federal Aviation Administration (FAA) first-class medical certificate was issued on December 5, 2015. According to the operator, the pilot was hired in 2012 and completed all required company training. At the time of the accident, he had accrued a total flight experience of about 6,347 hours of which 5,743 hours were in helicopters and 1,780 of those hours were in the same make and model as the accident helicopter. The pilot had flown 114 hours and 25 hours during the 90-day and 30-day periods preceding the accident, respectively; all of these hours were flown in the same make and model as the accident helicopter.

The copilot in the right seat held a commercial pilot certificate with ratings for rotorcraft helicopter and instrument helicopter. His most recent FAA second-class medical certificate was issued on May 16, 2016. According to the operator, the copilot was hired on July 31, 2016. He had completed company-required ground training and was in the process of completing flight training at the time of the accident. The copilot had accrued a total flight experience of 4,090 hours, all of which were in helicopters. Before the day of the accident, he did not have any flight experience in the same make and model as the accident helicopter but was qualified to act as second-in-command. AIRCRAFT INFORMATIONThe 41-seat capacity, tricycle-gear helicopter, serial number 61717, was manufactured in 1974. It was powered by two 1,500-horsepower General Electric CT58-140-2 turboshaft engines. The helicopter was maintained under a continuous airworthiness program. Its most recent inspection was a phase five check, which was completed on August 25, 2016. At that time, the airframe had accumulated 40,296.2 total hours of operation. The No. 1 engine had accumulated 708.9 hours since major overhaul (23,235 hours since new), and the No. 2 engine had accumulated 4,520.2 hours since major overhaul (26,259 hours since new). Following the phase five check, the helicopter had flown about 1.2 hours during the two previous FCFs. At the end of the second flight, prior to the accident flight, the flight crew reported total fuel onboard was 2,200 lbs. METEOROLOGICAL INFORMATIONAt 1353, the recorded weather at MLB, which was located about 8 miles north of the accident site, included wind from 070° at 11 knots, visibility 10 miles, and few clouds at 5,000 ft. AIRPORT INFORMATIONThe 41-seat capacity, tricycle-gear helicopter, serial number 61717, was manufactured in 1974. It was powered by two 1,500-horsepower General Electric CT58-140-2 turboshaft engines. The helicopter was maintained under a continuous airworthiness program. Its most recent inspection was a phase five check, which was completed on August 25, 2016. At that time, the airframe had accumulated 40,296.2 total hours of operation. The No. 1 engine had accumulated 708.9 hours since major overhaul (23,235 hours since new), and the No. 2 engine had accumulated 4,520.2 hours since major overhaul (26,259 hours since new). Following the phase five check, the helicopter had flown about 1.2 hours during the two previous FCFs. At the end of the second flight, prior to the accident flight, the flight crew reported total fuel onboard was 2,200 lbs. WRECKAGE AND IMPACT INFORMATIONThe helicopter came to rest upright in a field with no debris path noted. The wreckage was oriented on a magnetic heading of about 190°. A postcrash fire consumed the cockpit and cabin. The tail boom transition section exhibited partial thermal damage, and the tail boom remained intact. The five main rotor blades and the five tail rotor blades remained attached to their respective rotor hubs. The main and tail rotor blades exhibited signatures consistent with low rotational energy at ground impact. Four of the five main rotor blades exhibited partial thermal damage, and one main rotor blade exhibited thermal damage along its entire span. One tail rotor blade was fractured about 1 ft outboard of the attachment bolt; the outboard section of the separated blade was found on the ground next to the tailrotor. Another tail rotor blade was partially separated about 1 ft outboard of the attachment bolt, and its tip was embedded in the ground. Drivetrain continuity was confirmed between the main transmission and the tail rotor gearbox.

Both engines remained attached to the airframe and exhibited fire damage. Examination of the engines revealed that the first stage compressor blades of both engines exhibited little or no leading-edge damage. Both engine fuel control units were found with their respective control shafts in the "FLIGHT" position. Both engines were separated from the main gearbox at the aft end of the high-speed shaft. A boresope inspection of the helicopter's main gearbox was performed. No evidence of thermal damage was observed on the internal components of the main gearbox, and the interior coatings appeared in good condition. The gear teeth exhibited normal wear patterns consistent with typical service wear. No anomalous damage was observed with the gears and bearings. Additionally, the main rotor drive system was evaluated for continuity and all components operated normally. Manual rotation of the rotor brake disk resulted in corresponding movement of the main rotor head, tail takeoff pinion, No. 1 tail rotor drive shaft, and the two input pinion splined couplings (normally attached to the aft end of the high-speed shafts).

Freewheeling Units (FWU)

The left and right FWUs were subsequently examined at the manufacturer's facility. The ramp-roller clutch engaged on the right FWU when rotated in the drive direction and disengaged when rotated in the freewheeling direction. No anomalous damage was observed on the right FWU.

When the left FWU was rotated, the ramp-roller clutch remained disengaged and freewheeled in both directions of rotation. The splined nut was removed and exhibited no anomalous damage. Additionally, the ramps, roller elements, bearing cage, and bearing outer race did not exhibit anomalous damage. Further examination of the left ...