N433PH

HISTORY OF FLIGHT

On August 16, 2007, at 1513 central daylight time, a single-engine Bell 407 helicopter, N433PH, was not damaged during an emergency landing to the water in the Gulf of Mexico. The commercial pilot sustained minor injuries and the passenger was not injured. The helicopter was registered to and operated by Petroleum Helicopters Incorporated (PHI), of Lafayette, Louisiana. A company visual flight rules flight plan was filed for the on-demand air taxi flight that departed the East Cameron 109 (EC109) offshore platform at about 1507, and was destined for the West Cameron 98 (WC98) offshore platform. Visual meteorological conditions prevailed for the flight conducted under 14 Code of Federal Regulations Part 135.

In a written statement, the pilot reported that he departed the EC 109 platform and climbed to an altitude of approximately 1,000 feet and filed his flight plan with the operator's communications center. Approximately five minutes after departure, the engine chip light illuminated and the pilot immediately turned back to the departure platform. While in the turn, the pilot reported hearing a "high pitched grinding noise" and a "pop" before the engine stopped producing power.

The pilot entered an autorotation to the ocean as he made a Mayday call to his company's communications center. When the helicopter was approximately 75 to 100-feet-high above the water, the pilot initiated a flare to slow the helicopter's descent and attempted to deploy the emergency floats; however, he did not pull the handle hard enough. The pilot made a second attempt, which was successful, and the floats deployed when the helicopter was approximately 10-feet-high above the water. The pilot "pulled pitch" and the helicopter landed safely on the water with the floats fully inflated. Shortly thereafter, a large wave impacted the helicopter and broke out the right windshield and rolled the helicopter inverted.

The pilot and the passenger were able to exit the helicopter and deploy one of the on-board life rafts. Once both individuals were in the life raft, the pilot activated the EPIRB and another PHI helicopter was able to direct a nearby shrimp boat to the life raft. The pilot and the passenger were taken onto the boat and were later recovered by a United States Coast Guard helicopter.

PERSONNEL INFORMATION

The pilot held a commercial pilot certificate for rotorcraft-helicopter with a helicopter instrument rating. In addition, he was also a certificated flight instructor for rotorcraft-helicopter and instrument helicopter. The pilot held a current second-class FAA medical certificate and reported having accumulated a total of 1,855-hours, of which 139-hours were in the same make and model.

METEOROLOGICAL INFORMATION

The pilot reported the weather as wind between 180 and 220 degrees at 20, gusting to 25 knots, visibility 10 miles, broken ceiling 2,000 feet, and seas 6 to 10 feet.

ENGINE EXAMINATION

The engine was a Rolls-Royce M250-C47B, serial number S/N 847233. The M250 engine was a 2-spool turbo-shaft engine. Two power turbine (PT) stages drive the output shaft through a reduction gearbox. The gas producer consists of a compressor section, which has a single centrifugal stage driven by a 2-stage turbine. The combustion chamber is a cylindrical type. The engine power management system consists of a Hydro-Mechanical Unit (HMU), which is controlled by an Electronic Control Unit (ECU).

According to PHI maintenance records, the engine had accumulated 8,606.49 hours time since new (TSN) and of the turbine assembly had accumulated 1,904.7 hours time since new, 282.03 hours time since overhaul (TSO), and 439 cycles since overhaul at the time of the accident.

The engine was removed from the airplane at PHI facilities in Lafayette, Louisiana. The engine was partially disassembled under the supervision of the FAA with representatives from PHI, Bell, and Rolls Royce in attendance. Examination of the engine revealed signs of an uncontained engine failure near the area of the third stage turbine wheel. After the initial examination at PHI, the engine was shipped to Rolls Royce in Indianapolis, Indiana, where a Safety Board Power plants Engineer supervised a more detailed examination.

According to the NTSB Power Plants Group Chairman report, the examination included the removal of the upper and lower gearbox chip detectors, which both contained metallic debris. This debris was also found in the N2 speed pickup, oilcan and the oil filter. Scoring was noted on the oil scavenge pump's #6 and #7 bearing scavenge gear elements and cavities. The #1 and #8 bearing scavenge gear elements and cavities were not damaged.

The turbine module, which included the combustor and the gas producer turbine, were also examined. The combustor liner was intact. The fuel nozzle had previously been removed. The fuel nozzle swirler boss was cracked at the combustor chamber interface. The first stage nozzle shield was intact. The #8 bearing sump cover was deformed near the center consistent with contact with the gas producer turbine tie bolt. The third stage rotating labyrinth seal was intact. Approximately 150 degrees of the inner diameter was severely rubbed, which was consistent with contact against the #6 and #7 bearing housing. A 90-degree segment was worn completely through. The knife-edges were circumferentially and unevenly deformed, with an approximately 90-degree segment almost completely rolled-over. The PT inner shaft was intact; however, the inner race of the #6 bearing was severely deformed and spalled. The mid-shaft pilot ridge was deformed through approximately 120 degrees. The inner surface was corroded. The mating thread for the PT inner shaft spanner nut appeared to be undamaged. The PT inner shaft spanner nut appeared to be undamaged. The inner diameter of the PT inner shaft at the plane of the #6 bearing displayed rotational scoring as well as metal transfer, which was consistent with contact against the outer diameter of the turbine-to-compressor coupling.

The PT outer shaft was intact; however, there were two spiral fractures observed on the shaft. One spiral fracture was approximately 3-inches-long and originated between a crack within one curvic tooth and the mid-shaft. At the mid-shaft location, as the shaft wall thickens, the spiral direction changed 90 degrees and continued for approximately another half-inch. The second spiral fracture was approximately 180 degrees from the first and was approximately one half-inch in length with one end starting at the root of a curvic tooth. The loaded faces of the curvic-coupling teeth were galled. The fourth stage turbine connector nut was in its proper location and appeared to be undamaged. The deformable lock feature was still engaged with the nut. The easy removal of the nut from the shaft was hampered by the presence of a piece of curvic tooth fragment that was wedged between the nut and the shaft. Once the tooth fragment was removed, the nut rotated freely and was removed. The ring described by the forward face of the shaft, exhibited areas of polishing consistent with contact against the ring described by the aft face of the pinion gear. According to the Rolls-Royce metallurgical examination report, the fracture surfaces exhibited evidence of fatigue.

The gas producer tie bolt was fractured in two locations, which corresponded to the axial front and aft face planes of the first stage turbine disk segment. The outer case of the gas producer turbine bearing support was fractured in three locations. All three fractures were in the axial orientation and through the forward flange. One fracture had progressed through approximately 75 percent of the housing length and the other two had progressed through approximately 95 percent of the housing length. The #8 bearing cavity was wetted with oil and the bearing retainer sleeve appeared to be undamaged. All five inner housing support struts were deformed and one was fractured. The #8 bearing was intact but was rough when rotated by hand. A fractured portion of the aft stub shaft from the first stage turbine wheel was retained in the #8 bearing. The first stage nozzle was intact but ovalized and deformed. Additionally it was corroded on the vane surfaces, leaving an orange-brown discoloration. The trailing edge face was deformed and smeared due to impact in the radial direction consistent with non-concentric contact against the first stage turbine wheel.

The first stage turbine wheel was fractured into multiple pieces. Several of the peripheral fractured pieces were missing. Only four heavily deformed aft teeth of the curvic coupling remained attached to the hub. The first stage turbine energy-absorbing ring was deformed outward. The second stage nozzle was intact but deformed. The leading edge face was deformed and smeared due to impact in the radial direction consistent with non-concentric contact against the first stage turbine wheel. The first stage blade track and several vanes were fractured and missing. The trailing edge inner rim face was rotationally scored consistent with contact with the front face of the platform of the second stage turbine wheel.

The second stage turbine wheel was intact. All the curvic teeth were present but were all deformed and displayed score marks in the radial orientation. The leading edge blade platform was rotationally scored, consistent with contact against the vane platform of the trailing edge side of the second stage nozzle. The blade leading edges were dented and fractured due to impact. Small wedges of material were missing from the outer half-inch of all the leading edges. The forward stub shaft bearing land and spline appeared to be undamaged. The front pilot stub was rotationally scored. The PT bearing support was intact but the aft flange was deformed. Only the #7 bearing and the #6 to-#7 bearing spacer remained installed in the bearing suppor...