You’re in the cruise, everything’s stable. No warnings, no anomalies: just the hum of whatever normal sounds like 🚁
Then, out of nowhere, there’s a burning smell, followed by a fire, smoke in the cockpit, and a collective that requires your full body weight to stay down, but the helicopter keeps climbing!
This wasn’t a simulator drill. It was real, and none of this was triggered by pilot error…
In fact, it was pilot skill that got them out of it!
The crew didn’t have a checklist for what they ended up dealing with, yet they managed to descend, land, and walk away ✅
This Why Spotlight breaks down exactly what happened, why it happened, and what you as a pilot can learn from it.
Let’s take a look ⤵️
We don’t publish all our Notes from the Cockpit (like this one) publicly, some are shared only by email. Get the next one sent straight to your inbox ⤵️
💥 Accident Overview
On September 24, 2022, an AgustaWestland AW139 (N811TA) operated by Era Helicopters LLC experienced a critical inflight emergency while en route to Houma-Terrebonne Airport (HUM), Louisiana.
During cruise, the crew and passengers noticed a burning plastic smell. Minutes later, a loud “whoof” sound was followed by thick smoke that rapidly filled the cockpit, triggering multiple system warnings and an unresponsive collective.
The crew managed to clear the smoke by opening the left side cockpit window, which allowed them to further analyse what the problem was.
Despite full downward input on the collective, the helicopter continued climbing, and the pilots were forced to use cyclic pitch and manual engine mode switching to manage a high-speed descent without losing too much rotor RPM.
After an aborted landing attempt, a second approach involved switching engine 1 between idle and flight multiple times. At about 50 feet, the crew managed to perform a landing with both engines in idle.
The helicopter skidded off the runway following a hard landing, sustaining substantial damage, but all six occupants evacuated safely and uninjured.
A very impressive landing, all things considered.
⏱️ Timeline of Events
While cruising en route to HUM from an offshore rig, with about 7 minutes to go, the flight crew and passengers began to notice a burning plastic smell.
No smoke or abnormal indications were observed, so the crew shut off the air conditioning as a precaution.
Minutes later: A loud “whoof” was heard, followed by thick orange-brown smoke from the aft overhead circuit breaker panel. The cockpit rapidly filled with smoke, resulting in “zero visibility” in the cockpit:
Simultaneously, a rotor low warning sounded, both engines oversped, the collective control moved upward, and the cyclic moved left. All uncommanded.
The pilot in the left hand seat managed to clear the smoke by removing the left hand cockpit window.
The collective required full body weight to hold down, yet the helicopter continued to climb.
The aircraft climbed 3,500–4,000 ft uncontrollably despite the collective being pushed fully down.
Forward cyclic input was required to start the descent, at speeds of 170 – 186 knots, well above the Vne. It was the only way to make the helicopter descend.
A high-speed descent from 6,000 ft to 1,000 ft was initiated. An orbit was flown to check the gear extension and controllability with the help of ATC.
The crew could not manually control engine power via collective switches, so they toggled engine mode switches on the lower console instead.
The crew attempted to land with one engine in idle, but rotor RPM dropped to about 75%, which resulted in the crew initiating a go-around.
They began their second attempt, and as they were crossing 400 ft AGL, the crew started reduce the speed of the helicopter while alternating engine 1 from idle to flight to keep descending:
🔸 No. 2 engine remained at idle.
🔸 No. 1 engine was cycled between flight and idle to be able to decelerate and descend at the same time
🔸 When NR decreased to about 70% the No. 1 engine was returned to flight mode until NR increased to 85%, which is when the No. 1 engine was selected back to idle.
🔸 At about 50 ft AGL and roughly 70% NR, both engines were set to idle, which allowed the crew to land the helicopter.
The helicopter touched down with forward speed, skidded off the runway, and came to rest upright in grass. The main landing gear collapsed, but all aboard evacuated safely.
🔬 Investigation Findings
So, what happened?
The investigation by the NTSB found a misrouted electrical wire scraping against the C3 collective torque tube, which is located here:
The C3 torque tube is responsible for making sure the collective input from the pilots reaches the mixing unit, which transfers the movements to the rotor hub.
However, the electrical wire scraping caused:
🔸 an electrical short, which caused a:
🔸 Localised fire, which resulted in:
🔸 Thermal damage to the torque tube, which meant that:
🔸 The resin on the C3 torque tube was melting
This resulted in the start of the C3 torque tube moving, while the other end that is connected to the mixing unit was motionless, with the damaged tube in the middle. You can see the damage here:
How did that wiring get misrouted?
The culprit was a manufacturing error from 11 years prior:
🔸 The left-side wiring support strip had its plastic mounts installed on the wrong side (above the strip, instead of below the strip), which was caused by hard to read technical drawings (more on that below).
🔸 This incorrectly routed the wires above the strip instead of below, bringing them into contact with rivets on the C3 torque tube.
🔸 Although a similar error was found on the right strip, it did not result in chafing.
What about quality control?
After some further investigation, the NTSB found that the manufacturer’s technical drawings:
🔸 Provided ambiguous diagrams, especially for the left-side strip.
🔸 Lacked clear assembly verification steps for wire routing.
🔸 Right-side drawings were clearer, but the strip was still assembled incorrectly.
Here is the old drawing, where it is hard to make out if the wires go above or below the strip:
Here is the new updated drawing, which highlights and clarifies the fact that the wires should go underneath the strip, which increases the separation with the C3 torque tube:
Why wasn’t this caught earlier?
Despite regular inspections by the operator:
🔸 Scheduled checks did not include wire routing or clearance verification.
🔸 Wire routing in this area were not an inspection item, and clearance was likely adequate for most of the helicopter’s service life (until it wasn’t)
🔸 The wire damage likely progressed close to the accident date, making detection by chance the only possibility.
After the release of the service bulletin, Leonardo reported that an additional 23 helicopters were affected. Of these 23, 8 had incorrectly routed wire bundles, and 15 had evidence of chafing.
🧠 What Can We Learn From This?
🔸Tiny mistakes in design documentation can have massive downstream consequences
One missing diagram view or poorly labelled job card can allow incorrect assemblies to be installed and remain undetected for years.
🔸 Scheduled inspections won’t catch what you’re not looking for
Here is the crazy thing: the operator followed all inspection requirements!
But without a specific task to inspect the routing or mount orientation, the wiring passed every check. This went undetected for over 10 years. If you don’t know what you’re looking for, it becomes a lot harder to detect if something is wrong.
🔸 Redundancy in maintenance tasks matters
If a maintenance department or mechanic misinterprets a diagram, if there is no system-wide crosscheck, it might never be caught. Quality assurance programs and two-person engineering jobs can be part of the solution here.
🔸 Emergency handling skills matter
The crew handled an unprecedented and quite an extreme emergency: loss of collective control, combined with an inflight fire.
They used engine mode switches to creatively manage the descent, coordinated a two-attempt landing, and completed a successful “autorotation” from 50 ft.
None of these manoeuvres are in the rotorcraft flight manual!
🔸 Smells in the cockpit must be taken seriously
The flight began with just a smell, easily dismissed!
Within minutes, the cockpit was engulfed, visibility was lost, and critical systems failed. The link between a weird smell and losing your entire collective input is not easily made, but here we are. Expect the unexpected, every single flight!
💡 Conclusion
This AW139 accident involving N811TA highlights a chilling chain of failure where a single misassembled wiring support strip, installed more than a decade earlier, caused a near-catastrophic loss of control in flight.
The root issue wasn’t pilot error or weather. It was a manufacturing oversight, compounded by ambiguous documentation, and inspection gaps that allowed the error to exist for years!
The crew displayed some pretty incredible problem solving, and all six people walked away. But the event serves as a powerful reminder:
In aviation, the devil is in the detail, and sometimes that detail is hiding behind an ordinary clip, installed upside down…
You can find the final NTSB report here.
1 Comment
Anonymous · June 1, 2025 at 5:52 PM
Unfortunately manufacturing errors are much more common than any one of us would like to believe. Most with much less catastrophic consequences before they are addressed. I do think the authorities could look at the automotive manufacturing quality control systems such as the Toyota production system. Without doubt this needs to improve in helicopter manufacturing.