History of Flight
On September 24, 2022, about 1811 central daylight time, an Agusta AW139 helicopter, registration N811TA, was substantially damaged in an accident near Houma, Louisiana. The pilot, co-pilot, and four passengers were not injured. The helicopter was operating as a Title 14 Code of Federal Regulations Part 135 passenger flight.
About seven minutes before arrival at Houma-Terrebonne Airport (HUM), the flight crew and passengers smelled a "burning plastic" odor throughout the helicopter. No smoke was observed in the cockpit or cabin, and no abnormal cockpit indications were noted. The helicopter exhibited normal flight characteristics. The crew turned off the air conditioning as a potential source.
A few minutes later, a loud "whoof" sound occurred, accompanied by smoke from the aft portion of the overhead circuit breaker panel. Within seconds, the cockpit was engulfed in thick orange/brown smoke, resulting in zero visibility. Simultaneously, a rotor low audio warning sounded, both engines rapidly oversped, the collective control moved upward, and the cyclic control moved leftward.
The left-seat pilot could not clear smoke by opening the small ventilation window, nor could he open his door due to airspeed. He removed the left-side cockpit window, which cleared the smoke.
After visibility returned, the crew pushed the collective down and the cyclic forward and right. Significant force was required to maintain these positions. Power index reached about 145% on both engines with collective full down, and main rotor speed (NR) was slow to recover above 83% but eventually reached 100%. The helicopter climbed 3,500 to 4,000 feet because normal flight control inputs could not establish a descent. Selecting one engine to idle using engine mode switches caused NR to drop to the upper 70s, so the engine was returned to flight. Full body weight was needed to keep collective down, but the helicopter did not descend or slow down. Only by forcibly pushing cyclic forward did it descend, at 170 to 186 knots indicated airspeed.
The left-seat pilot declared an emergency with HUM tower and requested fire and emergency medical services. The crew briefed passengers.
Upon arrival over HUM, the crew conducted a high-airspeed descent from 6,000 to 1,000 feet, orbited to verify controllability, and had tower confirm the landing gear was extended. Unable to control engine power in manual mode using collective switches, they reduced No. 2 engine to idle using the lower console switch. With No. 2 idle and No. 1 at maximum continuous power, the helicopter decelerated to about 140 knots. The crew decided an autorotative landing was necessary to reach a safe landing speed.
On the first approach, they aligned with runway 36 at 140 knots with No. 1 in flight and No. 2 in idle. Selecting No. 1 to idle caused NR to drop from 100% to about 75%, so they returned to flight and executed a go-around.
On the second approach, they descended from 400 feet agl while alternating No. 1 between flight and idle, with No. 2 idle. By repeatedly switching, they descended to about 50 feet agl and decelerated to a speed where an autorotation was conducted with both engines idle. The helicopter landed on the runway with forward airspeed and skidded off the right side into grass.
After stopping upright, the right-seat pilot applied the rotor brake, stopping both rotors. The left-seat pilot shut off fuel and electrical switches. After passengers egressed, both engines were still running and were shut down by moving overhead engine control levers to full off.
Aircraft Information
The helicopter was assembled at the AgustaWestland facility in Philadelphia, Pennsylvania, in 2011. Assembly task job cards active at that time were originally issued in 2007.
The "Completion and Finishing of Power C/A Card" (No. 3G0630A04112C4R) contained instructions on routing electrical power cables from the cockpit nose to the cabin roof and power distribution panels. Drawings depicted cables routed under left and right wiring support strip assemblies. However, the shape of the left and right strip assemblies was identical on the job card despite actual differences. No specific instruction verified cables were routed underneath.
Subsequent closeout cards (Closings After Rain-Test Card and 3NB Pax Ceiling Panels Closeout Card, version 5) did not include wiring diagrams or inspection instructions. On December 20, 2014, version 8 of the 3NB Pax Ceiling Panels Closeout Card added two installation diagrams and a note about 0.5-inch clearance for flight control rods, but no wiring inspection instructions.
Manufacturing job cards for the wiring support strips: the left-side card (No. 3P5315A10531) had a single planform view; the right-side card (No. 3P5315A12931) had two views showing electrical supports mounted opposite the nut plates.
Recent Maintenance Inspections
At the time of the accident, the helicopter had an airframe total time (AFTT) of 7,491 hours. Era Helicopters, LLC (a Bristow Group subsidiary) operated and maintained the helicopter under an FAA-approved continuous airworthiness maintenance program (CAMP). The CAMP transitioned from Era to Bristow in July 2021, with FAA approval in August 2021.
AMPI Task 24-03 required a general visual inspection of bundles and connectors every 2 years, checking for corrosion, damage, chafing, and overheating. Under the Era CAMP, this task was in Phase 1 Inspection, last done on May 14, 2021, at 6,064.7 hours AFTT. After the CAMP reissue, it moved to Airframe Inspection B, last accomplished on August 1, 2021, at 6,246.4 hours (before FAA approval). No anomalies were noted.
AMPI Tasks 67-01 and -02 required inspection of flight controls and mixing unit, including the collective torque tube C3. Airframe Inspection A was completed on August 28, 2022, at 7,399.2 hours AFTT, with no anomalies. None of these tasks required inspecting the routing of wiring.
The helicopter accumulated 91.8 flight hours and 27 days between that inspection and the accident.