What happened
On November 29, 2023, an MD600N helicopter, registration N745MB, was engaged in a Part 133 rotorcraft external load operation near Sterling City, Texas. The flight, operated by Brim Aviation, was intended to perform aerial work on a power line system.
Prior to the accident, the crew arrived at a remote landing zone, conducted a safety meeting, and performed a pre-work scouting flight. ADS-B data indicates the helicopter departed the landing zone at approximately 1415 central standard time and approached a 133-foot steel monopole from the west. At approximately 1429, the tracking data terminated at the pole.
The helicopter sustained substantial damage and came to rest on its left side in a grass field, roughly 103 feet from the pole. The pilot and the aerial lineman sustained 2 fatal injuries.
The investigation
Investigators examined the wreckage and found impact marks on a 12-foot static arm at the top of the power pole. The main rotor blades exhibited significant deformation, fractures, and fragmentation consistent with an overload. The NOTAR system had separated from the fuselage, and the fuselage sustained extensive crushing damage.
An examination of the engine revealed rotational scoring in the compressor impeller and metal spray in the turbine section, which is consistent with the engine operating during the impact. No pre-impact mechanical malfunctions or failures were found in the airframe or engine that would have prevented normal operation.
Meteorological analysis showed that while the operator's manual listed a maximum wind speed of 40 knots, the area was experiencing wind gusts as high as 26 knots. Satellite imagery and sounding data indicated the presence of light turbulence and low-level wind shear (LLWS) at the time of the accident.
Additionally, a review of flight planning records indicated the pilot did not request weather information from Leidos Flight Service or through ForeFlight on the day of the accident. A search of archived data showed the pilot only updated route strings in ForeFlight on the day of the event.