SABINE PASS, TX, USA
N2906T
Mbb BO-105
The twin engine helicopter was en route to an oil platform located 90 miles south of Sabine Pass, Texas, in the Gulf of Mexico. The pilot called company dispatch and reported off Sabine at 0711 with 2.5 hours of fuel on board. The company's flight following radio log shows that the pilot made a normal position report at 0729 and reported that he was 67 miles from destination. The pilot transmitted another normal position report at 0744 and reported that he was 38 miles from destination. No other radio transmissions were received from the aircraft. According to the chief pilot, the altitude at which the helicopter would have been cruising at would most likely have been between 500 and 1,000 feet AGL. No abnormalities were discovered with the engines during detailed examinations. Tear down of the main transmission revealed that the sun gear had failed, thus resulting in the main rotor system not being driven. Structural deformations of the airframe revealed that the helicopter impacted the water vertically in a high rate of descent.
HISTORY OF FLIGHT On June 21, 1996, approximately 0750 central daylight time, a Eurocopter Mbb BO-105 CBS-4, N2906T, was destroyed after impacting water approximately 70 nautical miles south of Sabine Pass, Texas, in the Gulf of Mexico. The twin engine helicopter, owned and operated by Air Logistics Inc. as a Title 14 CFR Part 135 air taxi passenger flight, was en route to an oil platform located 90 miles south of Sabine Pass. All 4 occupants, the airline transport rated pilot and 3 passengers, were fatally injured. A company flight plan was filed and visual meteorological conditions prevailed. According to the company flight plan, the helicopter departed the Sabine Pass field base (95XS) at 0711 to transport 3 oil workers to High Island platform A-555. Company employees at the base reported that, the scheduled flight departed on time and nothing out of the ordinary was observed prior to and during departure. The pilot called company dispatch and reported off Sabine at 0711 with 2.5 hours of fuel on board (according to the chief pilot, 2.5 hours of fuel is "topped off" with approximately 1,020 lbs. of fuel). The company's flight following radio log shows that the pilot made a normal position report at 0729 and reported that he was 67 miles from destination. The pilot transmitted another normal position report at 0744 and reported that he was 38 miles from destination. No other radio transmissions were received from the aircraft. The company's published flight following procedures requires each aircraft to transmit position reports every 15 minutes after departure. The next position report was due from the accident aircraft at 0759. The pilots of 5 other aircraft which were monitoring the same company frequency at the time of the accident, reported that they did not hear any emergency transmissions or any unusual radio traffic. Although unlikely, it is feasible that a radio transmission from the accident aircraft between 0744 and 0759 could have been masked by other transmissions on that frequency. According to the chief pilot, the altitude at which the helicopter would have been cruising at would most likely have been between 500 and 1,000 feet AGL. No radar data was available to verify position or altitude (out of range for ATC coverage). PERSONNEL INFORMATION The pilot held a rotorcraft-helicopter Airline Transport Pilot Certificate with a VFR Commercial Pilot Type Rating in Cessna Citation 500, Airplane Single and Multi Engine -Instrument, CFI Rotorcraft-Helicopter, and an A& P Certificate. His current FAA medical certificate was second class with no limitations or waivers, and was dated June 6, 1996. He had been employed by Air Logistics as a helicopter pilot since August 15, 1983. His total flight time was approximately 20,459 hours, 18,692 of which were in helicopters. He had no history of previous accidents, incidents, or flight violations and his total experience in Gulf helicopter operations was 16 years (approximately 12,000 flight hours). According to a company check airman, the pilot demonstrated power recovery auto-rotations in a BO-105 helicopter during his most recent annual re-qualification on November 17, 1995. Full touchdown practice auto-rotations in the BO-105 were not practiced. Company records showed that the pilot completed re-qualification training in Bell BHT-206 helicopter on August 8, 1995. During this training the pilot accomplished two straight-in, and two 180 degree turn auto-rotations (full touch down). Additionally, company training policy requires pilots to demonstrate full touchdown practice auto-rotations to the water in Bell 206 helicopters. According to FAA regulations, there is no requirement to demonstrate full touchdown practice auto-rotations. According to company records, the pilot worked normal duty hours from June 13 through June 21. Personnel based at Sabine observed that the pilot seem to have had regular sleep cycles for work days prior to the accident. They stated that he usually was in bed (quarters located at the base) by 2300 each night. AIRCRAFT INFORMATION The MBB BO-105 CBS-4 (originally a CBS-2 model), serial number S-573 was manufactured in March, 1982, and the current Standard Airworthiness Certificate was issued on March 29, 1991. The helicopter was acquired by Air Logistics in November, 1995. Airframe total time at the time of the accident was 10,596.3 hours. The aircraft was being maintained in accordance with the Air Logistics Approved Aircraft Inspection Program (AAIP). The program contains a Daily Service Check (DSC), a 50 hour Preventative Maintenance Inspection (PMI), a series of 5 separate phase inspections conducted 150 hours apart, a 2,500 hour major airframe inspection, and "additional" maintenance items that are stand-alone inspections. The description and details of the inspection program are contained in the Air Logistics Maintenance Manual and is FAA approved. A detailed review of the aircraft maintenance records indicated that all of the inspections required by the AAIP had been complied with. A Daily Service check had been performed on June 20, 1996, the night before the accident. The last 50 hour PMI was performed on June 17, 1996, 20.2 flight hours prior to the accident. The last phase inspection (Phase 5) was conducted on June 16, 1996, 26.4 flight hours prior to the accident. Additionally, 300 hour swashplate, and 6 month float assembly inspections were conducted on June 15, 1996. Recent significant maintenance performed on the helicopter included the installation of the main transmission (S/N 1165) and main rotor assembly. Interviews of company maintenance personnel at the Sabine Pass, Texas, Air Logistics base, where the maintenance was performed, revealed that the main transmission and rotor assemblies were installed as a complete unit, (i.e. rotor system installed on the transmission). The tail rotor intermediate gearbox and tail rotor pitch change links were also replaced at the same time. The above maintenance was performed on June 15, 1996, and the aircraft flew 27 hours after the installations prior to the accident. Airworthiness Directive (AD) compliance was verified using the maintenance records and were visually inspected on the aircraft (during wreckage examination) for compliance. The non-applicable AD's were verified to be "non-applicable". All pertinent AD's were complied with and verified. A detailed review of the airframe maintenance records revealed no uncorrected defects or anomalies. The helicopter was powered by two Allison 250-C20B turbo shaft engines. Engine #1 (left side), serial number CAE-832097, had a total operating time of 11,861.0 hours. It was installed on the airframe on August 20, 1993. Engine #2 (right side), serial number CAE-830480, had a total operating time of 12,802.6 hours. It was installed on the airframe on August 15, 1990. A review of both engines' maintenance records revealed that all overhauls and inspections of the accessory, gearbox, compressor, and turbine sections were properly complied with, and no anomalies or uncorrected defects were found. Note: A detailed list of the last 90 days of verified maintenance history of the aircraft and a list of significant maintenance events for transmission, S/N 1165, are attached to this report. METEOROLOGICAL INFORMATION High Island weather station H08, located on platform HI 264, reported the following observation at 0730: 5000 scattered, 20 miles visibility, temperature 83 degrees, dew point 74 degrees, winds from 100 degrees at 10 knots, altimeter 29.92. Sea state reports ranged from 1 to 3 foot swells in the area of the accident. COMMUNICATIONS No distress calls were reported from the aircraft. WRECKAGE AND IMPACT INFORMATION At the request of the NTSB IIC, the wreckage recovery portion of the investigation was delegated to Air Logistics, party to the investigation. Recovery events were documented with under water video and still photography once the wreckage was brought to the surface. This documentation was valuable to the investigation team as it was used as a means of distinguishing recovery damage from impact damage. After 3 days of searching, a sonar contact was made at coordinates; North 28 degrees 27 minutes 84 seconds, West 94 degrees 15 minutes 24 seconds. At 1628 June 24, 1996, a diver confirmed contact with Air Logistics BO-105, N2906T. The location of the wreckage was oriented on line with a straight course from Sabine base to the intended destination (High Island platform A-555). The following information is submitted as the aircraft was found in-situ on the ocean floor: The divers found the helicopter laying on its left side with the skid mounted floats not deployed. The right float bag was torn away from the aircraft and the float bottle was exposed. The tail boom was found structurally separated from the fuselage and was only attached by wiring. The rotor head was attached to the mast and gear box, and all four blades were attached to the blade grips. Three of the blades were full length and appeared relatively undamaged. The fourth blade was found fractured approximately eight feet outboard. The under carriage was severely crushed upward and the fuel bladders were found exposed. After the extraction of the occupants, the aircraft was pulled to the surface. The rotor blades were cut off and marked to facilitate raising the wreckage to the surface. About twenty feet off the bottom, the main transmission began to separate from the fuselage. When the aircraft broke the surface, it had completely come apart. It was held together by the transmission mounting point on the right side of the transmission deck. At the conclusion of recovery operation, the aircraft had been submerged for approximately 157 hours. The recovery effort was completed in water temperatures of approximately 67 degrees and a water depth of 130 feet. All major components of the helicopter to include the main rotor blades, hub assembly, fuselage, tailboom, tail rotor drive shaft, flight controls, powerplants, skids, and hydraulic pack were found at the same location on the sea bottom. Aircraft parts found floating on the surface during the initial search included; 2 clam shell doors, the right side of the fairing that houses the tail rotor drive shaft from the intermediate gearbox to the 90 degree gearbox, the radio compartment door from the baggage compartment, a portion of the left engine air intake cowl, and a 6 inch by 36 inch piece of MRB skin. After recovery, the airframe and powerplant components were examined by the investigation team, under the direction of the NTSB investigator-in-charge. Deformation signatures throughout the structure and dynamic components showed evidence that the aircraft impacted the water with a high rate of descent, level pitch attitude, slightly left skid down, with minimal forward momentum. The following facts are presented as they were discovered by the investigation team during examination of the helicopter wreckage at a secure hangar facility: The cabin floor, which was found severely crushed upward, exhibited fractures across the span in the following locations: just aft of the pilots radio console; just aft of the forward cross tube; just forward of the main fuel tank; and just forward of the main tank fuel quantity probe. The bottom left side of the fuselage structure was crushed upward just inboard of the landing gear cross tube mount. The skid assembly was found intact and attached to the fuselage with the exception of 28 inches of the left front skid, which was found separated during the recovery. Cross tube support structure exhibited minimal deformation. The cabin roof was crushed downward and the main transmission mounts were found fractured in compression. Together with the turbine deck, the main transmission, rotor mast, and rotor head were displaced downward, forward and to the left. The 2 power levers on the overhead panel were found in the flight (full power) position; however, both levers may have been pulled to that position during the impact by the throttle control cables extending to the engine deck. Two indentations/slap marks were found on the throttle control quadrant adjacent to the throttle closed position. The indentations correlate to the width and movement of the power levers within the control quadrant. The mast moment indicator needle was found in the "yellow" range. The master caution panel was found intact on the instrument console. The panel was removed and a light bulb analysis was performed. Examination of the flight controls revealed the following: According to the manufacturer, the helicopter was originally equipped with dual controls; however, it was modified to facilitate a passenger in the left front crew seat. The left side pedals, cyclic, and collective were removed and properly covered. The pilot's control stick was bent in compression and the collective grip was fractured. All control rods in the nose section lower front fuselage were fractured in several locations due to overload. The control rods connecting to the tandem hydraulic unit were found fractured in compression overload. The tandem hydraulic unit was found basically undamaged with the exception of one hydraulic line, which was broken off. Examination of the 2-system hydraulic unit revealed that the helicopter was operating on the #1 system (i.e., the normal operating system). The connecting link between system #1 and system #2 was measured without removal and found to be 25mm. The specified value is 25.1mm. Both #1 and #2 system reservoirs exhibited normal filling and both filters were clean, and the buttons were not popped. The unit was free to move in all three axis. The boost control rods, "Lateral" & "Collective", were fractured in compressive overload and the "Longitudinal" rod was bent. The "Lateral" mixing lever exhibited bending rearwards. The swashplate, including input controls, were without visible damage. All rotating pitch links were attached and found to be properly fitted to the blade control levers. The blue pitch link rod was bent inward on its lower section. All main rotor blade controls were movable. In summary, no pre-existing problems were found in the flight control system. The tailboom was found intact and was connected to the main structure by lines and cables. The lower right portion of the boom exhibited compression damage upward along its length. The upper mounting rivets were found sheared toward the rear and the lower forward portion of the boom was buckled upward. The vertical fin was separated at the intermediate gearbox area. The failure appeared to be aft and to the right. The horizontal stabilizer was intact with the exception of the left vertical end plate lower end cap, which was missing. The stabilizer, outboard of the right end plate, was bent inboard toward the boom. The tail skid tube was bent slightly to the left. The tail rotor drive shaft was intact from just aft of the main transmission rearward to the intermediate gearbox. All couplings were found intact with the exception of the transmission gear box to short drive shaft, and the coupling connecting the tail rotor 90 degree gear box. All three drive shaft sections exhibited some degree of bending. The forward coupling (adjacent to the transmission gear box) showed evidence of tension with some torsion. The coupling to the 90 degree gear box exhibited evidence of tension. The #2, #3, and #4 bearing supports showed evidence of shifting aft from the impact forces. The intermediate gear box was found attached to the vertical fin. The couplings on the input and output sides of the box were found slightly distorted but intact. The gear box case was intact, but rotation by hand could not be accomplished; however, examination of the internal gears did not reveal evidence of sudden stoppage or oil starvation. The chip detector was dry and clean. No fluid was visible in the sight gauge. The 90 degree gear box was found connected to the upper vertical fin. It was intact and rotated by hand on both input and output. The chip detector was moist
The failure of the sun gear within the main transmission resulting in the main rotor system not being driven.
Source: NTSB Aviation Accident Database
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