Incident Overview
On April 15, 2019, at 0351 eastern daylight time, a Bell 206-L1+ helicopter, registration N395AE, sustained substantial damage during an accident near Fairview Park Hospital Heliport (48GA) in Dublin, Georgia. The pilot, flight nurse, and paramedic on board were not injured. The helicopter was operating as a Title 14 Code of Federal Regulations Part 135 emergency medical services flight.
Flight Sequence
The pilot reported the flight was intended to pick up a patient in Macon, Georgia, for transfer to a hospital in Augusta, Georgia. After completing a preflight inspection and normal engine start, the pilot applied power and entered a hover. He turned into the wind and prepared for an altitude-over-airspeed takeoff. A power check indicated a torque reading of 74.8%, and about 86% torque was used for the takeoff to clear obstacles. As the helicopter began to accelerate forward and gain climbout airspeed, the pilot heard a loud report from the engine deck area, followed by a clicking noise described as sounding like paper on fan blades. The helicopter immediately began to descend, then hit the ground and bounced, traveling to the right before coming to rest upright. The pilot rolled the throttle to idle and shut down the engine.
Postaccident Examination
Examination of the helicopter revealed that the vertical fin had separated due to contact with the main rotor blades, and the skids were spread. Fuel samples were free of debris and water, and no foreign debris was found in the engine intake area.
The Rolls Royce M250-C30P engine showed no obvious mechanical anomalies. When placed on a test stand, the engine did not start on the first two attempts. After removal, inspection, and reinstallation of the fuel nozzle, the engine started but ran at a higher than normal temperature, prompting termination of the test. Disassembly of the compressor module revealed that the diffuser had separated into two sections, exposing the vanes. Normally, these components are 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 Findings
The National Transportation Safety Board's Materials Laboratory conducted a metallurgical examination of the separated plate and ring section. The ring section had separated through the braze joint at the forward interfaces of the vanes. Orange paint was observed on the vanes, varying in width to almost the entire cross-section of the vane airfoil. Braze filler metal buildup was noted along the edges of some vanes. A metallurgical cross-section perpendicular through several vane airfoils revealed gaps at the interface between the braze metal and the airfoil surface, consistent with incomplete filler metal wetting. The presence of 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.
Manufacturing and Service History
The vane assembly was marked with FAA parts manufacturing approval (PMA) number 23051119AL Rev. F, serial number AEC12-070, FAA-PMA Il9D9. The diffuser was sold by EXTEX Engineered Products (formerly Timken Alcor Aerospace Technologies) 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 no additional data were available. EXTEX also had a 10-year retention policy, so detailed manufacturing history was no longer available.
A review of the compressor logbook revealed an entry by AAEO on April 7, 2006, indicating the zero-timed diffuser was installed in the compressor and sent to Air Evac EMS, Inc. The engine logbook showed that the diffuser had not been removed or repaired since installation. According to the operator, the diffuser had accumulated a total of 5,763.1 hours at the time of failure.