TAIC report reveals inspection lapses before helicopter crash

By Andrew Curran.

New Zealand’s Transport Accident Investigation Commission (TAIC) has released its final report into a July 2024 incident involving an Airbus AS350 BA helicopter that collided with terrain and came to rest on its left-hand side near the Paringa River mouth on the west coast of the country’s South Island.

On July 20, 2024, a pilot and passenger were repositioning the 43-year-old helicopter, ZK-HJM (msn 1671), from Queenstown (ZQN) to Franz Josef following maintenance by Salus Aviation. The helicopter was operated by Amuri Helicopters Limited, based at Hanmer Springs. Before the loss of ZK-HJM, the operator had three helicopters undertaking a variety of work around New Zealand.

The report, released on June 19, contained multiple findings including that it was “virtually certain” that the bolt securing the lower end of the left-hand hydraulic servo became detached during flight.

An uneventful flight, until it wasn’t

At the time of the accident, ZK-HJM had accumulated 13,043.2 flying hours since new. The pilot had a total flight time of 3,981 hours, including approximately 2,857 hours on the AS350 type. The passenger was the Amuri’s chief pilot. Both were taken to hospital with minor injuries after the crash.

The pilot had also flown the helicopter the previous day for a series of operational flight checks. The passenger, in their role as chief pilot, had also flown the helicopter earlier that day as part of the post-maintenance acceptance process.

However, just 50 minutes into the repositioning flight, the pilot reported feeling a slight jolt and commented that the main rotor blades appeared to have gone ‘out of track’.

The pilot and passenger discussed the condition and possible causes and initially chose to continue the flight. However, about seven minutes later, they decided to land near a settlement close to the Paringa River mouth.

When the pilot lowered the collective to descend, the out-of-track condition and vertical vibration became more pronounced. The cyclic control became harder to move to the left. Both noted the symptoms appeared consistent with a single hydraulic servo failure.

Immediately prior to landing, when the helicopter was about 10 to 20 feet above the ground, torque increased from approximately 40% to 60%, and the pilot stated that they were “out of control”.

The helicopter then began a roll to the left before hitting the ground and coming to rest on its left-hand side, facing approximately 180 degrees from the approach direction.

The passenger exited through the broken front left window. The pilot shut down the engine by closing the fuel lever before also exiting through the same window.

Missing bolt and nut

The pair inspected the helicopter and discovered a bolt missing from the lower attachment point where the left main rotor hydraulic servo connected to the transmission housing. They later found the bolt on the helicopter’s transmission deck, although the nut could not be located.

The fuel tank ruptured during the accident sequence but did not ignite.

Maintenance records showed the left and right hydraulic servos had been swapped during maintenance before the accident. The change was requested by the Amuri to balance wear on the components and improve the servo's service life as it became subject to higher workloads.

Impact damage showed that all four main transmission mounts failed in overload during the accident sequence. The right-hand hydraulic servo input rod fractured above the transmission deck, while the right-hand cyclic bell crank pivot bolt sheared at the threaded end below the transmission deck.

Before releasing the helicopter, two trained, qualified and authorised Salus engineers had completed the required duplicate safety inspection. However, the TAIC found it was “very likely” the engineers responsible for each part of the inspection were distracted and failed to adequately verify that the left and right main rotor servo swap had been completed correctly.

“It is likely that the engineer who certified the second part of the duplicate safety inspection was experiencing a level of cumulative fatigue that contributed to the error,” the report added.

Multiple findings about the helicopter crash

The TAIC made ten findings with varying degrees of certainty, ranging from likely to very likely and virtually certain.

• It found it was very likely that movement of the actuator bolt at the lower ball-end fitting manifested as the slight jolt and initial out-of-track condition experienced during flight.
• When the pilot lowered the collective to descend to the river for a precautionary landing, the torque reduced, which decreased the load through the main rotor control system, making it very likely that this allowed the loose bolt to fall completely free, thereby disconnecting the lower end of the hydraulic servo from the main gear box conical housing.
• The report found it was virtually certain the increase in torque occurred because the pilot raised the collective in response to a combination of reduced airspeed and the loss of translational lift.
• It was also very likely that the disconnected hydraulic servo, combined with the active hydraulic system, created an overwhelming load on the unassisted control system. This led to the helicopter rolling unintentionally to the left as the collective was raised on short final.
• The report concluded it was virtually certain that the bolt securing the lower end of the left-hand hydraulic servo became detached during flight, altering the helicopter’s control characteristics and influencing the outcome of the landing.
• TAIC also found it was virtually certain that the nut had not been tightened to the correct torque and that the locking pin designed to prevent it from loosening had either not been installed or had been installed incorrectly before the helicopter departed Queenstown.
• It was virtually certain that Engineer A did not complete the task of installing the left hydraulic servo. The report found it was very likely that Engineer A was distracted and working under time pressure before going on leave and failed to adequately verify the servo swap before signing the first part of the duplicate inspection certificate.
• The report also concluded it was likely that Engineer B was experiencing cumulative fatigue that contributed to the error.
• Overall, it was very likely that both engineers involved in the duplicate inspection were distracted and failed to verify that the left hydraulic servo had been correctly installed.

Four inspections failed to pick up the problem

Between the Salus engineers, the repositioning pilot and the chief pilot, four trained and qualified individuals inspected the helicopter before its repositioning flight. All were aware that the servos had been swapped, and all certified the aircraft as airworthy. However, the TAIC investigation zeroed in on Salus, whose engineers had certified the helicopter as good to fly.

The report found that Salus did not have a sufficiently robust quality assurance process to ensure maintenance activities were completed and documented in accordance with approved procedures.

“This increased the risk of maintenance errors not being identified and rectified,” the report noted.

In response, Salus is implementing a series of initiatives based on the International Association of Oil and Gas Producers Offshore Helicopter Recommended Practices. The company has also expanded its assurance action plan based on those standards.

“A second signature is not a safety control,” a TAIC statement said. “Duplicate inspections exist to catch errors before an aircraft returns to service. The protection depends on the quality of the inspection itself. If the inspection becomes a confirmation of paperwork rather than an independent verification of the work, critical errors can pass through undetected.”

“The maintenance organisation had procedures requiring duplicate inspections. But distractions, interruptions, time pressure and fatigue undermined the effectiveness of those defences.”

“The lessons in this report extend to all operators and maintenance providers to regularly review how critical work is checked, how interruptions are managed, and whether assurance processes are providing an accurate picture of day-to-day practice.”

You can read the full final report here.

Photos: TAIC, Google Earth.
Contact the writer: andrew@aerosouthpacific.com