CEN17FA112

The pilot's failure to maintain proper altitude resulting in a collision with water for reasons that could not be determined based on the available information.

The commercial pilot was repositioning the helicopter from an offshore oil platform to the operator's home base in visual meteorological conditions. When the helicopter did not return as expected, the operator initiated a search; the helicopter wreckage was found in a shallow marsh area just off shore. No radio distress calls were received from the pilot, and the skid-mounted emergency float system was not deployed. Onboard flight-following equipment recorded a straight flight path tracking directly to the intended destination with a gradual descent just prior to impact. Accident flight data extracted from the helicopter's engine control unit did not show any faults with the engine. Detailed examinations of the helicopter's airframe, drive system, and flight controls did not reveal any preimpact anomalies. Examination and full teardown of the engine did not reveal any anomalies and indicated that the engine was operating at the time of impact. Airframe deformations were consistent with a slightly nose-low and left-skid-down attitude at the time of impact; therefore, it is unlikely that the pilot experienced a loss of control. Given the absence of mechanical anomalies, the fact that the pilot did not make a distress call or activate the emergency float system, and the helicopter's relatively straight recorded flight path, it is likely that the helicopter was operating normally at the time of impact. Further, toxicology testing and autopsy findings did not indicate any evidence of pilot impairment. It could not be determined why the pilot failed to recognize the helicopter's descent and maintain a proper altitude above the water.

The Terrebonne Medical Examiner's Office, Houma, Louisiana, performed an autopsy of the pilot on February 28, 2017. The cause of death was blunt trauma. The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology testing of the pilot. No drugs, ethanol, or carbon monoxide were detected. At 0950, the weather observation at HUM included wind from 150° at 12 knots gusting to 17 knots, visibility 5 statute miles with haze, scattered clouds at 1,000 ft and a broken ceiling at 2,200 ft, temperature 24°C, dew point 21°C, and an altimeter setting of 30.12 inches of mercury. The search pilot reported that the conditions in the area of the accident site included 5-7 miles visibility with ceilings above 700 ft about 1130. The pilot held a commercial pilot certificate with rotorcraft-helicopter and instrument ratings. He was hired by Westwind Helicopters on July 17, 2016. His total flight time as of February 27, 2017 was 2,266 hours, all of which was in light helicopters. His total flight time in the accident helicopter make and model was 120 hours. He had flown 140 flight hours in single-engine helicopters in the 90 days before the accident. According to pilot training records provided by the operator, the pilot was current and qualified in offshore Part 135 flight operations. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued in June 2016 with no limitations. Westwind Helicopters leased the helicopter, serial number (S/N) 53182, from GM Leasing in April 2015. It had a total airframe time of 9,146.8 hours at the time of the accident. The helicopter was equipped with an Allison 250C47B turbo shaft engine (S/N CAE847222) with a total time of 15,510.6 hours. According to maintenance records provided by the operator, the most recent 100-hour inspection was completed on February 16, 2017, at 9,125.5 airframe hours. Maintenance records indicated compliance with all required scheduled maintenance inspections, applicable service bulletins, and applicable airworthiness directives. A review of the maintenance logbooks by the NTSB IIC did not reveal any uncorrected scheduled or unscheduled maintenance actions. General The wreckage was found in shallow marsh waters south of Timbalier Bay, about 15 miles south-southeast of HUM. The wreckage was recovered and transported to a salvage facility in Baton Rouge, Louisiana. The recovered portions included the main fuselage, tailboom, the main rotor drive system, main rotor blades, engine, tail rotor blades and tail rotor gearbox, and landing gear with skid-mounted float assembly. Detailed examinations of the recovered components were conducted under the supervision of the NTSB investigator-in-charge. The FAA, Westwind Helicopters, Rolls Royce, and Bell Helicopter participated in the airframe examinations at Southern Aircraft Recovery on March 2-3, 2017. The Rolls-Royce engine was examined under the supervision of the FAA on March 3, 2017, at Arrow Aviation, Broussard, Louisiana. The Engine Control Unit (ECU) was transported to Triumph Engine Controls in West Hartford, Connecticut, for data extraction. The following are summaries of the examinations. Airframe The airframe was destroyed by impact forces upon water contact, breaking into several pieces. Airframe deformations were consistent with a slightly nose low and left skid down orientation at the time of impact. The left forward Dzus fastener on the engine cowling that was reported loose at the ST37C platform was missing, and the cowling mounting hole was found fractured. The left side of the helicopter exhibited more damage than the right side, including doors, landing gear, and cockpit and nose area. The tailboom remained connected to the aft fuselage and the aft fuselage was separated from the aft engine firewall bulkhead. The tailboom was relatively intact with two slight bends to the left. The vertical fin exhibited a tail rotor strike to its bottom surface, consistent impact forces occurring after the tail rotor gearbox departed its mounting location. The skid-mounted float system was not deployed. Rotors All four main rotor blades exhibited spar and afterbody damage consistent with impact forces, but no spar fractures were observed. The top blade surface balance pocket weights located near the blade tips' leading edges were all intact, remaining firmly attached to the blade spars. The bottom blade surface balance pocket weights located near the blade tips' trailing edges had all departed from their mounting pockets in the blades afterbody surfaces. All four main rotor yoke arms were significantly damaged from impact forces, exhibiting delamination and fractures of the composite yoke flexure structure. All hub bearings were damaged consistent with overtravel. Up-stops and down-stops were significantly damaged, consistent with impact forces. Both tail rotor blades remained connected to their respective yoke arms. Both blades were relatively intact with one blade exhibiting trailing edge blade tip skin delamination consistent with impact forces. No pre-impact anomalies were found in the main or tail rotor systems and the damages found were consistent with rotation at impact. Flight Controls and Hydraulics The cockpit area was destroyed by impact forces. The helicopter was equipped with single controls at the pilot's station. The vertical tunnel where four vertical flight control tubes transit was found fractured consistent with impact at top and bottom surfaces. All four control tubes exhibited overload fractures at the top of the vertical tunnel and the right cyclic pitch control tube was found fractured in overload about 1 ft from the bottom of the tube. The cyclic was intact and remained connected to the control system. Cyclic movement revealed corresponding movement of the vertical control tubes. The collective was fractured at its cast base, consistent with impact forces. The collective jackshaft was intact but displaced due to extensive cockpit damage. Control linkages to the main rotor servos were found intact. All three main rotor servos and mounting support structures were intact, including intact nut and locking tabs at the spool valve wire drive to spool control lever connections. Tail rotor control system fractures were found at various locations due to airframe impact damage. The tail rotor pitch control was found intact. The hydraulic manifold was found intact and the hydraulic reservoir was full of hydraulic fluid. Both the pressure line to the manifold and the rotor brake hydraulic line were found fractured, consistent with overload forces. The bypass pop-out buttons for both the pressure and return lines were not extended. The hydraulic pump remained attached to the main transmission, but the elbow pressure fitting was found fractured consistent with impact forces. No pre-impact anomalies were found in the flight control or hydraulic systems. Drive System The mast was intact and the chip detectors were clean. The main KaFlex driveshaft exhibited flexure fractures at both forward and aft locations consistent with overload at impact. The KaFlex outer diameter exhibited minimal rotational signatures. The transmission end KaFlex coupling could not be rotated by hand. The top case of the transmission was removed, revealing significant magnesium corrosion from the transmission case between the planetary and ring gear teeth, preventing rotation of transmission gearing. All observed gears were intact. Transmission mounting to the airframe was secure. The fore/aft pylon elastomeric restraints were both damaged. The left restraint was found fractured consistent with overload impact forces and the right restraint was bent. The forward steel short shaft under the engine remained connected to the engine end, but the aft spline coupling separated from the oil cooler shaft due to airframe impact deformations just forw