History of Flight
On November 29, 2023, about 1430 central standard time, an MD Helicopters Inc. MD600N helicopter, N745MB, was involved in an accident near Sterling City, Texas. The commercial pilot and aerial lineman sustained fatal injuries. The helicopter was operating under Title 14 Code of Federal Regulations Part 133 as a rotorcraft external load flight, performing aerial work on a power line system. The operator was Brim Aviation.
Prior to the flight, the pilot completed the operator's flight risk assessment tool. The helicopter arrived at the remote landing zone (LZ) at about 1240. Between 1245 and 1310, the helicopter was configured for work and a safety meeting was held. A pre-work scouting flight occurred from 1315 to 1340, followed by another briefing upon return to the LZ.
ADS-B data showed the helicopter departed the LZ about 1415 and approached the target power line pole—a steel mono pole about 133 ft tall—from the west. The helicopter maneuvered around the pole, and data terminated at the pole about 1429. At 1440, the helicopter was overdue; the operator began communication attempts and searching. At 1551, the operator arrived at the accident site and discovered the wreckage.
Personnel Information
The pilot was employed by the operator and was signed off to perform Part 133 work two days before the accident. The aerial lineman was employed by Source Utility Services and was signed off to perform aerial lineman work on October 23, 2022. The lineman was secured to the cabin with two personal restraint lanyards and would stand on the left skid during work.
Aircraft Information
The FAA-Approved MD Helicopters MD600N Rotorcraft Flight Manual (RFM) states that, with a takeoff weight of 3,548 pounds and a density altitude of 3,278 ft, the helicopter would be operating within the controllability envelope for crosswind conditions. The RFM notes that hover in ground effect in winds over 17 kts has been demonstrated for all azimuths. The Brim Aviation General Operation Manual lists a maximum wind speed of 40 kts and a gust spread of 15 kts for flight operations.
Meteorological Information
Meteorological data indicated a mid-level trough west of the accident site, with cloud cover and increasing surface moisture moving from the south. Cloud base was likely between 2,000 and 3,000 ft agl with no precipitation below. Surface winds gusted as high as 26 kts, supported by HRRR soundings and wind farm sensors. A wind turbine 900 ft west-northwest of the site reported wind speeds between 18 and 22 kts near the accident time, with sustained-to-gust spreads of 10 to 15 kts. GOES-16 satellite imagery showed transverse banding in lower-level clouds, typically indicating turbulent conditions. Density altitude was 3,278 ft.
No turbulence or low-level wind shear was forecast, and no PIREPs indicated such conditions within 100 miles. The closest terminal aerodrome forecast, 42 miles southeast, had wind gusts to 21 kts. The pilot did not request weather from Leidos Flight Service or ForeFlight; it is unknown what weather information he checked.
Wreckage and Impact Information
Impact marks were observed on a static arm about 12 ft long atop the pole, about 4 ft from its base. The pole and attached wires were intact. The helicopter came to rest on its left side about 103 ft from the pole on a flat grass field surrounded by wind turbines. The fuselage sustained extensive crushing damage. The NOTAR system separated and was found 30 ft away. All major structural items were present. The main rotor system, fuselage, and empennage sustained substantial damage. Six main rotor blades exhibited deformation and fractures with overload signatures; two had blue paint transfer matching the tail boom. Flight control continuity was established.
Radiographs of the annunciator panel showed no hot filament stretching in any bulbs. The cockpit light panel similarly showed no stretched filaments. The engine had no preimpact mechanical malfunctions; rotational scoring and metal spray indicated operation during impact. Postaccident examination found no preimpact mechanical failures that would have precluded normal operation.
Flight Recorders
The helicopter was not equipped with a crashworthy voice or data recorder, nor was it required to be.
Medical and Pathological Information
Autopsies determined the pilot's and aerial lineman's cause of death as multiple blunt impact injuries. Toxicological testing of the aerial lineman detected delta-8-tetrahydrocannabinol (delta-8-THC) in cavity blood at a low level, along with its metabolite carboxy-delta-8-THC. Carboxy-delta-9-THC was detected in cavity blood and urine, but delta-9-THC was not detected. Vilazodone was found in cavity blood and urine. Delta-8-THC is a psychoactive cannabinoid that can impair motor coordination, reaction time, decision making, problem solving, and vigilance. Vilazodone, an antidepressant, may also impair coordination and judgment. The aerial lineman was not required to hold an FAA medical certificate.