FTW97FA051

This case was modified 6/26/2006.

The flight Sam 71 departed High Island 446, Gulf of Mexico at 1504, with a destination of High Island 105. At 1526, the pilot reported to Galveston flight following that the 'tail [rotor] gear box chip light [had] illuminated,' and he was experiencing a 'very high vibration,' which 'settled down a little bit at a slower airspeed.' At 1527 the pilot reported heading towards a platform 3 miles to his north. At 1531 Sam 71 reported that on his first attempt to land on the platform [High Island A20], he was 'not able to control the tail rotor.' Sam 71 also reported that he would try to land one more time, and if unable he would 'continue in [Galveston].' There were no further communications with Sam 71. Examination of the tail rotor system revealed one pitch change link disconnected.

This case was modified 6/26/06.

History of flight

On November 28, 1996, at 1533 central standard time, an Eurocopter AS350B2 helicopter, N6100U, owned and operated by Petroleum Helicopters, Inc.(PHI), as a Title 14 CFR Part 135 flight on demand air taxi flight, was destroyed during an emergency landing at the High Island A20 platform in the Gulf of Mexico. Visual meteorological conditions prevailed, and a company VFR flight plan was filed. The airline transport rated pilot and two passengers were fatally injured. The flight originated from High Island 446 platform, Gulf of Mexico, at 1504, and was en route to its destination of High Island 105 platform.

According to company flight following records, at 1526 the pilot reported that the "tail [rotor} gear box chip light [had] illuminated," and he was experiencing a "very high vibration," which "settled down a little bit at a slower airspeed." At 1527, he reported heading towards a platform 3 miles to his north. At 1528, he reported being 2 miles from the platform. Then at 1531, the pilot reported that on his first attempt to land on the High Island A20 platform, he was "not able to control the tail rotor." He also reported that he would try to land one more time, and if unable, he would "continue in [to Galveston]." There were no further communications with the pilot. Company flight following transcripts show the pilot's call sign is Sam 71.

Personnel information

The airline transport rated pilot had accumulated a total of 5378 flight hours, of which 53.5 hours were in the AS350B2 helicopter. On September 16, 1996, he completed recurrent training, and demonstrated competency in the Bell 206 helicopter in accordance with FAR 135.295(b). On November 2, 1996, he completed transition training in the AS350B2 helicopter, and demonstrated competency in accordance with FAR 135.295(b).

Aircraft information

The helicopter had a total airframe time of 1,815 hours and 50 minutes at the time of the accident, and its maintenance records indicated that both tail rotor pitch change links were original equipment. On the night of November 27, 1996, a daily inspection of the aircraft was completed, and no cracks were observed in either tail rotor pitch change links.

On the morning of November 28, 1996, the accident aircraft had a transmission oil pressure switch changed at High Island 568. The pilot performed a preflight inspection of the helicopter, and was observed checking the area of the tail rotor. After the maintenance and preflight was completed, an operational check was performed by the pilot. Subsequently, the aircraft was released for flight, and flown approximately 5 hours prior to the accident.

A review of the airframe and engine records by the FAA inspector did not reveal any anomalies or uncorrected maintenance defects. According to the maintenance records, on October 10, 1996, the tail rotor gearbox had been changed.

An estimate of the weight of the helicopter at the time of the accident placed it within weight and balance limits.

Wreckage impact information

The aircraft wreckage was located approximately 25 nautical miles south southeast of Galveston, Texas, in the Gulf of Mexico, approximately 35 feet from the High Island A20 platform in about 50 feet of water. The tail rotor and vertical stabilizer were separated from the tailboom, and found approximately 50 to 100 feet from the main fuselage. All major components were recovered, except approximately 42 inches of tailboom, which included the horizontal stabilizer, and approximately 53 inches of tail rotor drive shaft.

The High Island A20 platform's first level is 90 feet above the water and has a radio tower and crane on its northwest side. A heliport is located 30 feet above the first level and it extends beyond the east corner of the first level. Examination of the platform revealed no evidence that the helicopter had contacted the heliport; however, there was damage to the roof of the platform control shed, which is located on the level below the heliport. Several holes were found in the southwest corner of the roof, and the right skid steel extension was found on the roof. Blue and yellow paint transfers were also found on the southwest corner of the roof. Helicopter debris was found on this level and on the level below. See the enclosed wreckage diagram.

Examination of components and a reconstruction of the helicopter was performed at PHI's maintenance facility, Lafayette, Louisiana, on December 3 and 4, 1996. The examination revealed that the aircraft's cabin section was destroyed; however, the instrument panel was relatively intact. The tailboom was attached to the fuselage by wires, and the tail rotor drive shaft cover showed rotational scars at the engine to tail rotor drive shaft coupling.

The engine was intact and had shifted forward. The power turbine and freewheel moved freely, and the compressor section was locked. The tail rotor output showed extensive rotational damage.

The main rotor head was intact with the yellow, red and blue star arms failed in a near 45 degree angle, leading edge outboard to trailing edge inboard. The main rotor blades had some damage and were connected to the rotor head. All pitch change rods were intact, and the main rotor servos were all connected. See the enclosed American Eurocopter report for further details.

The tail rotor was connected to the gearbox, which was still mounted to the tailboom. The tailboom, with the vertical fins attached, was separated just aft of the horizontal stabilizer. The tail rotor blades had some damage, and there was damage to the slider and yoke. One pitch change link on the tail rotor side was fractured and separated. The bearing was still attached to the pitch change horn and was worn.

Examination of the non separated pitch change link bearing revealed it had .003 inch radial and .008 inch axial play. The control rod bearing at the control lever had .011 inch radial and .028 inch axial play, and the pitch change spider spherical bearing had .030 inch radial and .053 inch axial play. Since a "TRGB Chip" light was reported, a teardown of tail rotor gearbox was performed. Metal shavings, and ferrous and non-ferrous materials were found in the gearbox.

The disconnected pitch change link and materials found in the tail rotor gearbox were shipped to the National Transportation Safety Board, Office of Research and Engineering, Materials Laboratory, Washington, D.C., for further examination and evaluation.

Flight control continuity was established to the main rotor system, and to the tail rotor system where the pitch change links attach to the tail rotor.

Medical and pathological information

An autopsy was performed by Korndorffer, W.E., M.D., of the Medical Examiner's Office for the County of Galveston, Texas. Toxicological findings were negative.

Tests and research

On January 22, 1997, the disconnected pitch change link and materials found in the tail rotor gearbox were examined at the National Transportation Safety Board, Office of Research and Engineering, Materials Laboratory. The examination of the fractured pitch change link revealed fatigue cracking emanating from the loop end containing the bearing assembly. Most of the scrim cloth was missing from the raceway of this bearing assembly. The larger of two fatigue cracks emanated from an area containing small corrosion pits. A fatigue striation count was not performed on this fatigue fracture because of environmental exposure. A fatigue striation count was performed on the smaller fatigue crack less exposed to the environment. The count yielded 737 striations. See the enclosed metallurgist's report for details of the ferrous and non-ferrous materials examination, and for further details on the pitch change link examination.

Eurocopter France reported that there were two similar occurrences of tail rotor pitch