Dublin, GA, USA
N395AE
Bell 206
The pilot said that he heard a noise from the engine deck followed by a "clicking" noise as he was starting to accelerate the helicopter forward on takeoff. The helicopter immediately began to descend then impacted the ground and bounced before coming to rest upright. The main rotor blades flexed and severed the vertical stabilizer. Examination of the engine's compressor section revealed the diffuser had separated into two sections, exposing the vanes. The diffuser is comprised of individual vanes that are brazed between two annular plates and a third support ring to form one solid diffuser assembly. Metallurgical examination of the separated plate and ring section revealed that the ring section separated through the braze joint at the forward interfaces of the vanes due to a large amount of incomplete braze joint surfaces on the vane airfoils. The vane assembly was marked with a Federal Aviation Administration parts manufacturing approval number. A search of the manufacturing history of the diffuser revealed that the part was sold to a turbine engine overhaul company about 13 years before the accident. The diffuser, which was zero-timed, was installed in the compressor and sent to the operator. A review of the engine logbook revealed that the diffuser had not been removed/repaired since it was installed on that date and that it had accrued a total of 5,763.1 hours at the time it failed. According to the company that sold the diffuser to the overhauler, any manufacturing history on the diffuser was no longer available due to the company’s 10-year retention policy for manufacturing records.
On April 15, 2019, at 0351 eastern daylight time, a Bell 206-L1+ helicopter, N395AE, sustained substantial damage when it was involved in an accident near Fairview Park Hospital Heliport (48GA), Dublin, Georgia. The pilot, flight nurse, and paramedic were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 emergency medical services flight. The pilot stated that the purpose of the flight was to pick up a patient in Macon, Georgia, for transfer to a hospital in Augusta, Georgia. He said he completed a preflight inspection, and the engine start was normal. Once the preflight checklists were completed, the pilot applied power and pulled the helicopter into a hover. He then turned the helicopter into the wind and prepared to make an "altitude over airspeed" takeoff. The pilot completed a power check with a torque reading of 74.8% then used about 86% torque to accomplish the altitude over airspeed takeoff to clear obstacles. As the helicopter started to accelerate forward and gain climbout airspeed, the pilot heard a loud report from the engine deck area. The engine then made a "clicking" noise that he described as sounding like paper on fan blades. The pilot said the helicopter immediately began to descend then hit the ground and bounced. It traveled to the right before it came to rest upright. The pilot rolled the throttle to idle and shut down the engine. A postaccident examination of the helicopter revealed the vertical fin was separated by contact with the main rotor blades and the skids were spread. Fuel samples taken from the helicopter were absent of debris and water, and there were no obvious signs of foreign debris in the engine intake area. Examination of the Rolls Royce M250-C30P engine revealed no obvious mechanical anomalies. It was placed on a test stand to be run. The engine did not start on the first two attempts. The fuel nozzle was removed, inspected, and then reinstalled. Another start was attempted, and the engine started. Once the engine was stabilized at idle it, was observed to run at a higher temperature than normal and the test run was stopped. The compressor module was then disassembled, and the diffuser was found separated into two sections, exposing the vanes (whereas these components are normally brazed together as one piece). The braze joints from the event engine were no longer securing the forward annular plate to the remainder of the diffuser. Metallurgical examination of the separated plate and ring section was conducted by the National Transportation Safety Board's Materials Laboratory. The examination revealed that the ring section separated through the braze joint at the forward interfaces of the vanes. Orange paint was observed on the vanes and varied in widths to almost the entire cross-section of the vane airfoil. Braze filler metal buildup was observed along the edges of some of the vanes. A metallurgical cross-section was prepared perpendicularly through several vane airfoils. Gaps were observed at the interface between the braze metal and the airfoil surface. The gaps between the braze metal and the vane surfaces were consistent with incomplete filler metal wetting in the braze joint. The presence of the orange paint on the vane cross-sections indicated areas where the braze metal did not wet the base metal. The separation of the ring from the plate was likely due to the large amount of incomplete braze joint surfaces on the vane airfoils. The vane assembly was marked with Federal Aviation Administration (FAA) parts manufacturing approval (PMA) number: 23051119AL Rev. F, Serial number: AEC12-070, FAA-PMA Il9D9. A search of the manufacturing history of the diffuser revealed that EXTEX Engineered Products (formally Timken Alcor Aerospace Technologies) sold/shipped the diffuser to Action Aircraft Overhauled Engines (AAEO) in Dallas, Texas, on April 5, 2006. AAEO does not retain work order records longer than 10 years (only required to keep for 2 years), so there was no additional data available. EXTEX also had a 10-year retention policy. As such, any detailed information regarding the manufacturing history of the diffuser was no longer available. A review of the compressor logbook revealed an entry by AAEO on April 7, 2006, indicating the diffuser, which was zero-timed, was installed in the compressor and sent to Air Evac EMS, Inc. A review of the engine logbook revealed that the diffuser had not been removed/repaired since it was installed. According to the operator, the diffuser had accrued a total of 5,763.1 hours at the time it failed.
A partial loss of engine power on takeoff due to separation of the diffuser assembly as a result of incomplete braze joint surfaces on the vane airfoils.
Source: NTSB Aviation Accident Database
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