Over a year after Lulutai Airlines’ SAAB 340B (A3-PUA) veered off a Tongan airport taxiway and hit “a disused refuelling bund,” investigators have published their final report.
All three crew members and 35 passengers evacuated the aircraft without injury, but the aircraft sustained significant structural damage. It has since been repaired and returned to service, the Deputy Prime Minister Taniela Fusimālohi previously said.
The investigation was conducted by the Tongan Civil Aviation Office, with the Office serving as the chief investigator.
The investigator found that the flight crew misdiagnosed a tripped circuit breaker as a hydraulic fluid leak, leading to improper handling of the emergency.
The circuit breaker had cut power to critical hydraulic indicators, but the first officer failed to identify it during initial troubleshooting—likely due to “expectancy error.” Believing they had a hydraulic leak, the crew shut off the hydraulic pump, which had been functioning normally, leaving the system without pressure, the 50-page report says.
Despite following parts of the hydraulic loss checklist, the crew did not complete all steps and had only a basic understanding of the system’s limitations.
After a safe landing, the captain decided to taxi toward the terminal, believing residual brake pressure was sufficient.
However, hydraulic pressure depleted near the terminal, causing a loss of braking and directional control, “resulting in the aircraft veering off the apron and the collision.”
Maintenance Failures and Unrecorded Defects
The investigation uncovered additional safety lapses including that the aircraft’s flight data recorder (FDR) was not recording critical information due to a malfunctioning data acquisition unit.
The issue had been incorrectly attributed to a high-frequency radio problem, leading to a misdiagnosis.
The unit’s circuit breaker had been manually locked out eight days before the incident, yet the defect was neither properly documented nor repaired in accordance with maintenance protocols.
The report says: “This was due to a flight data acquisition unit having an internal fault which resulted in its circuit breaker tripping. The fault identified by the tripped circuit breaker, went unrectified as it was misdiagnosed as an issue with the aircraft’s high frequency radio system, and had been isolated with a locking collar to prevent resetting likely 8 days before the accident.”
Missing Underwater Locator Beacon
Further scrutiny revealed that the cockpit voice recorder’s underwater locator beacon (ULB)—a crucial device for locating wreckage in water—had been removed at least five months prior to the accident.
Despite its absence, no entry was made in the aircraft’s technical logbook to record the deficiency or prompt corrective action.
Systemic Logging Lapses
While routine maintenance tasks appeared to be consistently recorded, these two critical defects—the inoperative FDR and missing ULB—were overlooked entirely.
The omissions raise concerns about oversight in the airline’s maintenance documentation processes, particularly for safety-critical systems.
While the airline’s CEO was seated in the cockpit jump seat, investigators found no evidence of interference in the crew’s decision-making.
Safety Recommendations
The report highlighted several key areas requiring improvement, including enhanced crew training on hydraulic system failures and stricter adherence to checklist procedures.
It also emphasised the need for more rigorous oversight of maintenance logging and timely defect rectification.
Additionally, the report stressed the importance of ensuring that critical recording systems, such as the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR), are fully operational before flight to support effective incident investigations and safety measures.
Lulutai Airlines has since reviewed its procedures to prevent similar incidents. The accident underscores the importance of accurate troubleshooting, thorough checklists, and proper maintenance documentation in aviation safety.
