The Lulutai Airlines aircraft which exited the taxiway and hit an embankment at Fua’amotu Airport had lost its hydraulic systems after a circuit breaker tripped, the Tonga Civil Aviation Office has found.
On 8 December 2023, a Lulutai Airlines Saab 340B was operating a scheduled passenger flight from Fua’amotu International Airport, Tongatapu, to Lupepau’u Airport, Vava’u.
On descent into Vava’u, the flight crew identified an issue with the aircraft’s main hydraulic system and elected to return to Fua’amotu.
After a safe landing in Fua’amotu, the flight crew planned to stop on the runway in accordance with the abnormal checklist for hydraulic fluid loss.
But with brake pressure remaining, and without a tug readily available, the crew opted to taxi to the terminal.
During the taxi, the aircraft lost wheel braking and direction control due to the depletion of hydraulic pressure, resulting in the aircraft veering off the apron and colliding with a disused refuelling bund, collapsing the right landing gear leg. The three crew and 35 passengers were uninjured.
To conduct an independent investigation of the accident, Tonga’s Minister for Infrastructure appointed a Chief Investigator for the Tonga Civil Aviation Office, Mr James Panuve, in accordance with Tonga’s Civil Aviation Act 2020 (Revised Edition). The Australian Government supported the investigation through the Australian Transport Safety Bureau, appointing an Accredited Representative in accordance with International Civil Aviation Organization Annex 13.
“The investigation found a tripped circuit breaker removed power from the hydraulic quality indicator, and 2 of the hydraulic pressure indicators,” Mr Panuve said.
While the investigation could not determine when the circuit breaker tripped during the flight, the tripped circuit breaker was not detected by the first officer during troubleshooting, most likely due to expectancy error.
“As they did not notice the tripped circuit breaker, the flight crew misidentified the hydraulic indication issue as a hydraulic leak,” Mr Panuve explained.
“They therefore commenced the abnormal checklist for hydraulic fluid loss, which included turning off the hydraulic pump. This resulted in no hydraulic pressure being automatically provided to the hydraulic system.”
While the abnormal checklist instructs flight crews to stop the aircraft on the runway, during the approach and after landing at Fua’amotu the flight crew discussed the possibility of taxiing after landing.
“After landing the captain recognised they had brake pressure remaining, and that there was not a readily available aircraft tug,” Mr Panuve said. “They then continued to taxi the aircraft back to the terminal.”
When close to the terminal, hydraulic pressure depleted and the aircraft lost wheel braking and directional control, leading to the accident.
Mr Panuve said the accident highlighted the necessity for flight crews to accurately assess system functionality when in-flight system issues arise, and to follow checklists in their entirety.
“Vigilance when assessing aircraft system status is vital to minimising opportunities for error,” he said. “The importance of training, following standard procedures, and effective communications is well established for aviation safety.”
In response to the investigation, Lulutai Airlines has identified several corrective actions, including reviewing maintenance practices and integrating lessons learnt from the accident into their procedures.
Read the final report: Prime Minister’s Office Website