N811TA

HISTORY OF FLIGHTOn September 24, 2022, about 1811 central daylight time, an Agusta AW139 helicopter,

N811TA, was substantially damaged when it was involved in an accident near Houma,

Louisiana. The pilot, co-pilot, and 4 passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 passenger flight.

According to a statement provided by the flight crew, about 7 minutes before arriving at Houma-Terrebonne Airport (HUM), Houma, Louisiana, the flight crew and passengers smelled a “burning plastic” odor throughout the helicopter. The flight crew observed no smoke in the cockpit or cabin, confirmed that there were no abnormal cockpit indications, and that the helicopter exhibited normal flight characteristics. The flight crew decided to turn off the air conditioning in case it was the source of the odor.

The flight crew reported that a few minutes later there was a loud “whoof” sound accompanied by smoke emanating from the aft portion of the overhead circuit breaker panel. Within a few seconds the cockpit was engulfed with a “thick orange/brown smoke” that resulted in “zero visibility” in the cockpit. The flight crew simultaneously encountered a rotor low audio warning with a rapid overspeed of both engines and observed an upward movement of the collective control and a left movement of the cyclic control.

The left-seat-pilot was unable to clear the smoke from the cockpit by opening the small ventilation window on the left-side cockpit door. The left-seat-pilot was also unable to open his cockpit door due the helicopter’s airspeed; however, he was able to remove the left-side cockpit window, which cleared the smoke from the cockpit.

After the smoke cleared from the cockpit, the flight crew pushed down the collective control and the cyclic control was pushed forward and to the right. The flight crew reported that both the cyclic and collective controls required significant force to keep in position. The power index (PI) was about 145% on both engines with the collective control full down, and the main rotor speed (NR) was slow to accelerate above 83% but it eventually recovered to 100%.

The helicopter rapidly climbed a total of 3,500 to 4,000 ft because the flight crew was unable to establish a descent using normal flight control inputs. The flight crew attempted to establish a descent by selecting one of the engines to idle using the engine mode switches on the lower console panel, but the NR quickly decreased from 100% to the upper 70s. The engine at idle was returned to a flight condition using the engine mode switch. The flight crew reported that “full body weight” was required to keep the collective control down, but the helicopter did not descend or decrease its airspeed with the collective control down. The flight crew noted that the only way to get the helicopter to descend was to forcibly push the cyclic control forward, but the helicopter descended at 170 to 186 knots indicated airspeed (KIAS).

The left-seat-pilot declared an emergency with the tower controller at HUM and requested fire and emergency medical services be notified. The flight crew then briefed the passengers about the emergency.

After the helicopter arrived over HUM, the flight crew conducted a high-airspeed descent from 6,000 ft to 1,000 ft, where an orbit of the airport was flown to verify flight controllability and to have the tower controller confirm that the landing gear was extended. The tower controller confirmed that the landing gear was extended. As the helicopter orbited the airport, the flight crew was unable to control engine power in manual mode using the switches on the collective control. The flight crew then attempted to reduce the helicopter’s airspeed by reducing the No. 2 engine to idle using the engine mode switch on the lower console. With the No. 2 engine selected to idle the helicopter decelerated to about 140 KIAS with the No. 1 engine at maximum continuous power. The flight crew then decided that an autorotative landing would be the only way to further reduce the helicopter’s airspeed to a safe landing speed.

On the first landing approach, the flight crew aligned the helicopter with the runway 36 centerline at 140 KIAS with the No. 1 and No. 2 engines in flight and idle modes, respectively. The No. 1 engine was selected to idle to further reduce airspeed for landing, but the NR rapidly decreased from 100% to about 75% before the flight crew selected the No. 1 engine to flight mode and a go-around was completed.

On the second landing approach, the flight crew began the descent from 400 ft agl while progressively decreasing the helicopter’s airspeed by alternating the No. 1 engine between flight and idle modes with the No. 2 engine still selected to idle. Consistent with the first landing approach, NR rapidly decreased with both engines selected to idle; however, during the second approach, when NR decreased to about 70% the No. 1 engine was returned to flight mode until NR increased to 85% when the No. 1 engine was selected back to idle. By alternating the No. 1 engine between flight and idle modes, the helicopter descended to about 50 ft agl and decelerated to an airspeed where an autorotation was conducted with both engines at idle. The helicopter landed on the runway with forward airspeed and skidded off the right side of the runway into a grass area.

After the helicopter came to a stop upright, the right-seat-pilot applied the rotor brake, which stopped both rotors and the left-seat-pilot turned off all fuel and electrical switches. After ensuring that the passengers had safely egressed the helicopter, the flight crew noted that both engines were still running. The engines were shut down by moving the overhead engine control levers to the full off position. AIRCRAFT INFORMATIONHelicopter Assembly Tasks and Manufacturing Job Cards

The helicopter was assembled at the AgustaWestland facility in Philadelphia, Pennsylvania, in 2011. The assembly task job cards active at that time were originally issued in 2007.

When the helicopter was assembled, the Completion and Finishing of Power C/A Card, No. 3G0630A04112C4R, contained instructions on the installation and routing of electrical power cables from the cockpit nose area to the cabin roof and subsequently to the power distribution panels. Figure 1 is a drawing excerpt from the job card depicting the cable routing in the cabin roof.

Figure 1. A drawing excerpt from the “Completion and Finishing of Power C/A Card” showing the power cable routing on the cabin roof with left and right wiring support strip assemblies. (Courtesy of Leonardo Helicopters, modified by NTSB)

The assembly cards contained views of the left and right wiring support strip assemblies installed with power cables routed through them. In the views looking upwards (from within the cabin), the power cables were depicted as solid lines with the strip assemblies as solid lines behind them, implying that routing of the power cables were under the strip assemblies, as shown in Figure 2 and Figure 3. The shape of the left and right strip assemblies was identical on the assembly job card, despite the right strip assembly being a different shape than the left strip assembly. The assembly job cards provided no specific instruction to verify that the power cables were routed underneath the strip assemblies.

Figure 2. A detail excerpt from the Completion and Finishing of Power C/A Card showing the power cable routing under the right strip assembly. (Courtesy of Leonardo Helicopters, modified by NTSB)

Figure 3. A detail excerpt from the Completion and Finishing of Power C/A Card showing the power cable routing under the left strip assembly. (Courtesy of Leonardo Helicopters, modified by NTSB)

When the helicopter was assembled, the Closings After Rain-Test Card, No. 41269352, did not include any diagrams or photos of the wiring assembly nor did it provide instructions regarding inspection of the wiring in the overhead panel.

The 3NB Pax Ceiling Panels Closeout Card, version 5, replaced the Closings After Rain-Test Card. The task card also did not include any diagrams or photos of the wiring assembly, nor any instructions regarding overhead wiring.

On December 20, 2014, after the helicopter was assembled, the 3NB Pax Ceiling Panels Closeout Card was updated to version 8, and included two installation diagrams, shown below as Figure 4 and Figure 5.

Figure 4. Diagram from 3NB Pax Ceiling Panel Closeout Job Card (Red ellipses were added for emphasis by NTSB)

Figure 5. Diagram from 3NB Pax Ceiling Panel Closeout Job Card (Red ellipses were added for emphasis by NTSB)

The updated job task card also included the statement, “Ensure that the moving parts of the flight control rods in the area has at least 0.5 inch clearance from the surrounding fixed parts.” However, the updated job task card did not mention nor provide specific instructions for the inspection of wiring in the same area.

Wiring Support Strip Manufacture

At the time of its manufacture, the manufacturing job card for the left-side wiring support strip assembly, No. 3P5315A10531, contained only a single planform view of the strip assembly, as shown in Figure 6. According to Leonardo Helicopters, the solid drawing lines for the nut plates (anchor nuts) versus the dashed drawing lines for the electrical supports implied that the electrical supports were mounted on the side opposite that of the nut plates.

Figure 6. The single view of the left strip assembly in its manufacturing job card. (Courtesy of Leonardo Helicopters, modified by NTSB)

At the time of its manufacture, the manufacturing job card for the right-side wiring support strip assembly, No. 3P5315A12931, contained two views of the strip assembly, as shown in Figure 7. These two views of the strip assembly distinctly show that the electrical supports were mounted on the side opposite that of the nut plates.

Figure 7. The t...