CEN14FA004

A total loss of engine power due to the liberation of a second stage turbine blade near the blade root due to a high-cycle fatigue crack and subsequent overload. Although extensive testing and materials analysis was performed, the reason for crack initiation could not be determined.

As the helicopter departed from the oil platform's helipad, witnesses heard a "pop" followed by a high-pitch screeching noise coming from the back of the engine. The helicopter nosed-over and dove into the water with the emergency floats extended. Examination of the engine revealed that one of the second-stage turbine disk blades had liberated due to a high-cycle fatigue (HCF) crack. The crack propagated until the blade separated due to material overload, which resulted in extensive damage to all of the third-stage turbine disk blades and most of the fourth-stage turbine disk blades. Metallurgical analysis of the liberated blade revealed no material anomalies. According to the engine manufacturer, there was no history of second-stage turbine blade failure due to HCF at the same spanwise position as the accident blade. A dynamics analysis of the second-stage turbine wheel revealed no mode crossing within or above the normal engine operating range that would be consistent with HCF initiation at the point where the blade failed. Several potential failure scenarios were also evaluated; however, none yielded any evidence to support the blade failing as it did. The engine was not equipped with an engine-monitoring system that could have identified any anomalies that may have initiated the HCF crack or contributed to the failure of the second-stage turbine blade. Although the surviving passengers stated that the platform was not venting methane at the time of the accident and an eyewitness said he did not see methane being vented, platform operating records revealed that methane was being vented continuously on the day of the accident. However, the actual volume of methane released at the time of the accident and whether it was ingested into the engine on takeoff could not be determined. The HCF crack was a pre-existing condition and was not the result of a sudden ingestion of methane on the day of the accident. A low-level of diphenhydramine, a sedating antihistamine, was detected in the pilot's blood and urine, but it could not be determined if it impaired the pilot's ability to operate the helicopter.

HISTORY OF FLIGHT On October 9, 2013, about 0720 central daylight time, a Bell 206L-3, N54LP, was substantially damaged when it impacted water shortly after takeoff from the Main Pass (MP) 107D oil platform in the Gulf of Mexico. The commercial pilot was fatally injured and the three passengers were seriously injured. The helicopter was registered to and operated by Panther Helicopters, Inc., Belle Chasse, Louisiana. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed for the business flight, which was destined for the Belle Chasse Heliport (06LA), Belle Chasse, Louisiana. The flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 135. The purpose of the flight was a routine crew change at the MP107D oil platform, which consisted of dropping off three oil platform employees, picking up three other employees, then returning to 06LA. The pilot and three passengers departed 06LA about 0633 and flew direct to MP107D. After landing on MP107D, the pilot did not shut down the helicopter and stayed at the controls with the main rotor turning until the crew change was complete. A witness standing on the MP108E oil platform, which is about 300-to 400 yards from MP107D and affords a clear and unobstructed view of the MP107D platform, saw the helicopter sitting east-southeast on the helipad with its main rotor blades turning. The witness said three people got off the helicopter and three other people got on. He described the weather as " stale " and the wind sock was " limp. " About 1 to 2 minutes later, the witness observed the helicopter pull up into a 3 to 4-foot-high hover over the helipad and make a slight bearing change toward the east. He said that, at that point, everything was completely normal with the helicopter. The helicopter then moved forward and started to take off toward the east. The witness said as soon as the helicopter cleared the helipad's skirting, he saw a flash and a large (10-foot-high x 10-foot-wide) "poof " or " cloud " of white smoke come from directly under the main rotor blades near the exhaust section of the helicopter. This was followed by a loud, high-pitched, screeching noise, as if the engine were being revved up. The witness said this " poof " of smoke occurred when the helicopter was parallel to a flare boom that extended directly out from the platform and was positioned on the north side of the helipad. The helicopter then nosed over toward the water; cleared the helipad's skirting and did not strike the flare boom as it descended. The witness said he saw the helicopter's emergency floats fully expand before it impacted the water. The helicopter hit the water hard with the main rotors still turning; became completely submerged and rolled inverted. The witness could see the helicopter's skids near the surface of the water and noted that one emergency float (he could not recall which) had completely separated from the helicopter. The witness did not see any occupants coming to the surface and used his very high frequency handheld radio to issue a " may-day-call. " He also directed a field boat, which was at the base of the MP108E platform, to the helicopter. He said that by the time the boat arrived, two deck hands had already stripped down and jumped into the jellyfish-infested water to help the helicopter occupants. They were able to get three of the four occupants out of the helicopter and onto the field boat despite one of the deckhands having an allergic reaction to the jellyfish stings. The witness said he did not see any methane gas being vented from the flare boom on the morning of the accident; however, he did see a large (size of an automobile) " methane cloud " coming from the flare boom the day before the accident between 12 and 5 pm. The methane cloud was located where he saw the white smoke on the day of the accident. The witness said he has seen methane being vented from the MP107D flare boom on several occasions and that " a lot of gas " is vented several times a week. In a telephone interview, one of the passengers on the helicopter (Passenger 1), stated that he had just completed a 14-day " hitch " on the MP107D oil platform and was headed back to Louisiana. On the morning of the accident, he and the two other platform employees prepared the platform for a crew change and waited for the helicopter to arrive. Once it had, he loaded his bags and was the last of the three passengers to board the helicopter. He boarded the helicopter via the left rear door and sat in the rear left seat, facing forward. He then donned an inflatable life vest, put on a headset, and fastened his seatbelt making sure it was secure and snug. Passenger 1 said that once everyone was fastened in, they gave the pilot a " thumbs-up " and the pilot prepared to depart. At this point, everything regarding the flight was " normal. " He said the helicopter lifted up from the platform and began forward flight. When the helicopter was over the water, he heard a loud noise overhead as if the transmission was coming a part. The passenger who was seated next to him (Passenger 2) asked, " What's that? " to which Passenger 1 responded," hold on. " He reported that they then hit the water with a " big splash. " Before impact, he did not hear any alarms going off in the cockpit and did not remember the emergency floats expanding. The pilot did not say anything during the accident sequence. Passenger 1 stated that he may have passed out for a few minutes. When he regained consciousness, he realized he was out of his seatbelt (he did not recall unfastening the buckle). The helicopter had rolled on-to its left side, and he tried to find the door. When he tried to stand up, he realized he couldn't feel his legs. At this point, Passenger 2 had opened the right door and was climbing out. Although water was entering the cabin, he and the passenger who seated in the front left seat (Passenger 3) were able to keep their heads above water. There was no movement or response from the pilot. Passenger 1 said that he remained where he was for a few minutes, and when the helicopter began to roll inverted, he was able to push himself out of the right rear door. He then tried to inflate his life vest, but when he pulled on the inflation-lanyard it would not inflate. He said that he was not familiar with this particular model vest and he did not try to self-inflate. Shortly after, Passenger 3 was able to get out of the helicopter. Passenger 1 said that while the deckhands were working to extract the pilot, Passenger 2 was dragged to a life-boat via a life-ring. At this time, Passenger 1 saw a life vest floating in the water. He was able to inflate it and used it to support himself until he was rescued. Passenger 1 said that he was in a " panic state of mind " and did not recall getting onto the boat. He said the platform was not venting methane at the time of the accident. In a telephone interview, Passenger 2 said that once the helicopter landed, he placed his bags in the cargo bay and walked around the front of the helicopter. He boarded the helicopter and said in the right rear seat, facing forward. He donned the provided inflatable life vest, a headset, and fastened his seatbelt assembly. He said he did not talk to the pilot or notice anything unusual about his behavior. After all three passengers were onboard, the pilot asked if they were ready to go and they responded they were ready. The employee said the pilot then simultaneously brought the helicopter up off the pad and forward. He described the takeoff as "kind of shaky." He said that on other flights, pilots will normally bring the helicopter into a hover, do an instrument check, and then start forward flight. However, in the three times he had flown with the accident pilot, he always took off without hovering. Passenger 2 said that once the helicopter moved off the he