FTW01FA017

The helicopter departed from a helipad located on an offshore oil platform, and was 3 minutes from landing at a refueling helipad on another platform, when the pilot transmitted two distress calls indicating the helicopter was "going down." There were no witnesses to the accident; however, 9 minutes after the distress calls were heard, the helicopter was found floating inverted in 3-4 foot seas. Subsequently, the helicopter sank and was later recovered and examined. Examination of the helicopter revealed no anomalies with the airframe or flight control systems. Examination of the engine revealed that the first and second stage turbine blades were fractured due to extreme heating. One blade of the second stage tubine disk had liberated from its retention slot, and all the blade roots and retention slots of this disk exhibited permanent outboard deformation, due to a combination of centripetal forces from engine operation and excessive heat. In contrast, the blade roots and retention slots of the first stage turbine disk did not exhibit evidence of outboard deformation, most likely since they were located further away from the heat source. The rear bearing assembly (located aft of the second stage disk) was contaminated with coke. The coking suggests that oil was leaking from the engine and migrating from the rear bearing assembly. The aft side of the second stage turbine disk displayed dark stain marks in the form of streaks. A passage exists that would allow oil to flow from the rear bearing to the aft face of the second stage turbine disk. Oil that strikes the disk would flow into the hot stream of gases and auto-ignite, starting a fire. Oil migration can occur if the rear bearing scavenge and vent tubes become blocked; however, the scavenge and vent tubes were checked during the engine examination and were not found blocked.

History of flight

On October 28, 2000, at 1637 central daylight time, an Aerospatiale AS-350BA single-engine helicopter, N26WW, was destroyed when it impacted water during a forced landing following a loss of engine power near the East Cameron area, block 200, in the Gulf of Mexico. The instrument rated commercial pilot, sole occupant of the helicopter, received fatal injuries. The helicopter was registered to Textron Financial Corporation Inc., of Fort Worth, Texas, and operated by Tex-Air Helicopters Inc., of Houston, Texas. Visual meteorological conditions prevailed, and a company visual flight rules (VFR) flight plan was filed for the 14 Code of Federal Regulations Part 91 positioning flight. The flight originated from East Cameron 231A (EC231A), an offshore oil platform located in the Gulf of Mexico, at 1630, and was destined for Abbeville, Louisiana, with an intermediate fuel stop at Vermilion 200 (V200), another offshore oil platform.

According to dispatch records and the pilot of another helicopter (N118TA), at 1635, the pilot of N26WW stated the he was en route to V200 and was three minutes from landing. At 1636, the pilot of N118TA heard the following distress call: "118, I'm going down." Before the pilot of N118TA could respond he heard a second distress call during which he heard: "118, Whiskey Whiskey going down one mile from you." The pilot of N118TA reported that he could hear a "warning horn," whose sound could not be positively identified, as the pilot of N26WW transmitted the distress call. No other distress calls were received. The pilot of N118TA then initiated a search for N26WW.

At 1645, the pilot of N118TA located the accident helicopter floating inverted. According to a global positioning system (GPS) receiver in N118TA, N26WW was located at north 028 degrees 44.28 minutes latitude and west 092 degrees 37.80 minutes longitude, approximately 75 miles southeast of Cameron, Louisiana. The pilot did not observe any survivors or inflated personal floatation devices. Each of the helicopter's six skid floats were observed inflated. One of the floats remained attached to the skid assembly and the remaining five were floating beside the helicopter. At 1650, the float that remained attached to the skid detached, and the helicopter sank.

On November 4, 2000, the helicopter was recovered to a secure facility at the Clover Field Airport, Houston, Texas.

Personnel information

On April 26, 1992, the pilot was issued a commercial pilot certificate, with rotorcraft-helicopter and instrument rotorcraft-helicopter ratings. He also held airplane single and multi-engine land ratings. According to a training form, provided by Tex-Air Helicopters Inc., the pilot completed initial training for the AS-350 on June 4, 1999, and underwent his most recent FAR Part 135 competency/proficiency check on July 31, 2000. According to the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), which was completed by Tex-Air Helicopters Inc., the pilot had accumulated a total of 3,591.4 flight hours, of which 3,481.1 were in rotorcraft, and 856.8 were in the AS-350. On October 6, 2000, the pilot was issued an FAA second class medical certificate, with no limitations.

Additionally, the pilot had completed an offshore water survival course on June 19, 1998.

Aircraft information

The 1980-model black, white, and red helicopter (serial number 1229) was equipped with a three bladed, semi-articulated main rotor system and a 681-horsepower Turbomeca Arreil-1B turboshaft engine. The helicopter was operated in Japan from the time of its inaugural flight in 1985 through 1998.

On July 23, 1991, the engine (serial number 757) was removed from another AS-350, overhauled, and installed in the accident helicopter. At the time of the overhaul, the engine had accumulated a total of 1,958.06 hours and the airframe had accumulated a total of 3,959.05 flight hours. During the overhaul, the first and second stage turbine discs were replaced and modifications were performed to module three (which houses the high pressure section of the gas generator with the power turbine), which changed its overhaul interval from 2,000 to 2,500 hours.

On October 18, 1994, the helicopter was involved in a mid-air collision; which damaged its tailboom and horizontal stabilizer. The records revealed that the helicopter was then stored in Japan for a period of four years.

During 1998, the helicopter was imported to the United States. On October 6, 1998, repairs to the damage that was incurred during the mid-air collision were completed, and the helicopter was converted from a B model to a BA model by Arrow Aviation of Broussard, Louisiana.

On October 8, 1998, the helicopter was issued an FAA standard airworthiness certificate, at which time it had accumulated a total of 4,779.8 flight hours. The engine had accumulated a total of 2,778.8 hours.

On May 18, 2000, the engine's rear bearing oil scavenge pipe was flow checked for clogging. According to the Turbomeca Maintenance Manual (05-10-02), each operator is required to perform this check every 100 hours of engine operation. Clogging of the rear bearing oil scavenge pipe could result in oil residue collecting, in the form of coke, in the area of the rear bearing. Coke is a hard, crystalline residue of turbine engine oil. According to a maintenance log card provided by the operator, the rear bearing oil flow was less than the allowable limits. The engine was removed from the airframe, disassembled to allow servicing of the rear bearing, and subsequently, the engine was reassembled and reinstalled in the airframe. Additionally, the engine was modified to incorporate TU 281, 282, and 283 engine modifications. According to Turbomeca Service Bulletin N 292 72 0215, the modifications "improve cooling of the gas generator rear bearing and reduce the formation of coke deposits in this area." The airframe had accumulated a total of 6,198.0 flight hours and the engine had accumulated a total of 4,197.1 hours when the work was accomplished.

On October 10, 2000, the engine underwent its most recent 100-hour inspection, and had accumulated a total of 4,687.4 hours.

On October 24, 2000, the airframe underwent its most recent 100-hour inspection and had accumulated a total of 6,731.0 flight hours.

On October 27, 2000, 50 gallons of Jet-A fuel were added to the helicopter's 143 gallon capacity fuel tank. According to the operator's daily flight logs for October 27th and 28th, the helicopter had completed 14 flights since the last refueling, and would have had approximately 40 minutes of fuel on board at the time of the accident.

At the time of the accident, the airframe had accumulated a total of 6,733.9 flight hours, and the engine had accumulated a total of 4,733.0 hours. According to the maintenance records, all flow checks of the rear bearing subsequent to May 18, 2000, were complied with, and no clogging was found. Additionally, it was determined that module three of the engine had accumulated 2,774.9 hours since overhaul, which was 274.9 hours over its 2,500 hour overhaul interval.

Meteorological information

The pilot of N118TA reported the following weather conditions near the accident site; scattered clouds at 5,000 feet, visibility 10 miles in haze, wind from 100 degrees at 12 knots, and seas 3-4 feet.

Wreckage and impact information

A review of an underwater recovery video revealed that the helicopter came to rest on its left side. The rotor brake lever was in the released position, the fuel flow control lever (throttle) was 1/4 out of the flight gate in the emergency operating range, and the emergency fuel shutoff lever was in the open position (normal ready position).

The recovered wreckage was examined by the NTSB investigator-in-charge, representatives from Tex-Air, and a representative from American Eurocopter. The cabin area