DFW05LA180

The 17,291-hour commercial helicopter pilot was on short final approach to a helipad on an offshore platform when he heard and felt a "bump" in the flight controls, followed by vibrations in the tail rotor pedals and a loss of tail rotor effectiveness. The pilot immediately landed the helicopter and preformed a normal engine cool-down. Inspection of the helipad found no evidence of a tail rotor strike. A post-accident inspection of the studs, that hold the tail rotor gearbox to the tail boom, revealed signs of low-cycle bending fatigue. Additional inspection under a microscope of the studs, showed evidence of high loads during bending. The 90-degree tail rotor gear-box teeth, displayed typical wear pattern and did not show any sign of misalignment. One of the tail-rotor blades was heavily damaged and missing a portion of the outer blade. The remaining end of the blade was slightly torn and contained gray paint or material at the leading edge. The material was later examined, and found to contain a high concentration of zinc. Examination of paint chips in the impact area on the vertical fin showed no zinc in the paint. The object that impacted the tail rotor blade could not be identified or located during the course of the investigation.

On July 11, 2005, approximately 0930 central daylight time, a twin-engine Bell 430 helicopter, N430CV, registered to, and operated by Chevron/Texaco USA, Inc., of Picayune, Mississippi, was substantially damaged during a forced landing following a loss of directional control while landing at the Main Pass 30 offshore oil platform, located in the Gulf of Mexico. The commercial pilot and two passengers were not injured. Visual meteorological conditions prevailed, and a company flight plan was filed for the 14 Code of Federal Regulations Part 135 flight. The air taxi flight originated from Venice, Louisiana, at 0846, en route to several offshore oil platforms.

According to a statement submitted by the 17,291-hour pilot, the flight departed [oil platform] Main Pass 41M for a 6.2 nautical mile flight to Main Pass 30. He stated that he was the first one to land at that offshore platform that day. While on short final to the helipad, he heard and felt a "bump" in the flight controls, followed by vibrations in the tail rotor pedals and a loss of tail rotor effectiveness. The pilot immediately landed the helicopter and preformed a normal engine cool-down and shut down.

The two passengers aboard the helicopter submitted statements. The following are excerpts from their statements:

The first passenger reported that "we approached the deck about 3 or 4 feet above the deck and I heard a loud bang, felt like a missile hit us coming from the back. Once the [helicopter] shut-down, we got out to see what happened and noticed the damage, and could not find any evidence where we hit." The passenger further stated that, " I can't believe that the tail hit the skirting because we could not see any evidence. It may have been a small piece of debris on the deck because of the storm."

The second passenger reported that "as we were landing 4 to 5 feet above the deck, we hit something in the back." "I did notice 4 birds on the deck as we were landing." The passenger added, "we [got] out of the aircraft and could not find any evidence that we hit something, seems like to me that something came up and hit the blade."

Examination of the helicopter by the operator and a Federal Aviation Administration (FAA) inspector revealed that the top portion of the vertical fin was missing, the tail rotor gearbox had broken from its mount, and one of the tail rotor blades was severed in half.

On July 27, 2005, an FAA Inspector visited the helipad and reported that he found no evidence of a tail rotor strike.

The parts of the tail rotor assembly damaged in the accident were shipped to the manufacturer's laboratory for further investigation. Inspection of the parts was conducted on 1 September 2005, by representatives of the NTSB, the manufacturer, and the FAA.

A review of the helicopter's maintenance records revealed that on a periodic inspection of the tail rotor assembly conducted on January 4, 2004, two studs that hold the tail rotor gearbox to the tail boom, were found broken. The records show that maintenance personal, in accordance with instructions from the helicopter manufacturer, repaired and returned the helicopter to service. An email between maintenance and the manufacturer, indicated that the failed studs may have been retained for further analysis, however, no disposition on the studs were found.

During the accident sequence on July 11, 2005, the replacement studs holding the gearbox failed. Inspection of the bolts revealed signs of low-cycle bending fatigue. Additional microscopic inspection of the failed bolts, showed evidence of high loads during bending.

The 90-degree tail rotor gear-box splines displayed typical wear pattern and did not show any sign of misalignment.

One of the tail-rotor blades was found heavily damaged and missing the outer portion of the blade. The remaining end of the blade was slightly torn and contained gray paint or material at the leading edge. The material was later examined, and found to contain a high concentration of zinc. Examination of paint chips in the impact area on the vertical fin, revealed that the helicopters paint did not contain zinc.

The object that impacted the tail rotor blade was not found during the course of the investigation.