What happened
On 8 December 2023, a Lulutai Airlines SAAB 340B, registration A3-PUA, was performing a scheduled domestic flight from Fua’amotu International Airport to Lupepau’u Airport. During the descent, the flight crew noticed that the main hydraulic system quantity indicator showed zero and there was no indication of fluid in the tank.
Believing the aircraft was experiencing a hydraulic leak, the crew initiated the abnormal checklist for hydraulic fluid loss. This procedure included turning off the hydraulic pump, which inadvertently stopped the automatic provision of pressure to the system. The crew decided to return to Fua’am to address the issue. After landing successfully using the auxiliary hydraulic system, the crew elected to taxi to the domestic terminal rather than waiting for a tug. During the taxi, the aircraft lost wheel braking and directional control as hydraulic pressure was depleted. The aircraft subsequently veered off the taxiway and collided with a disused refueling bund, causing the right landing gear leg to collapse. There were no injuries among the 35 passengers and 3 crew members.
The investigation
The investigation examined the aircraft's electrical and hydraulic systems, as well as maintenance records. Investigators discovered that a tripped circuit breaker had cut power to the hydraulic quantity and pressure indicators. This breaker was not identified by the first officer during troubleshooting, likely due to an expectancy error.
Furthermore, the investigation revealed that the flight data recorder was not functioning because a flight data acquisition unit had an internal fault that tripped its circuit breaker. This fault had been misdiagnosed as a radio issue and was left unrectified with a locking collar. Additionally, the underwater locator beacon and its mounting bracket had been removed from the aircraft at least five months prior to the accident. These maintenance discrepancies, including the missing beacon and the unrectified electrical fault, were not documented in the aircraft's technical log.
Findings
- The crew misidentified a failed electrical indicator as a physical hydraulic leak.
- The crew failed to identify a tripped circuit breaker that was causing erroneous hydraulic system indications.
- The crew did not follow the entirety of the abnormal checklist, specifically failing to recognize the implications of turning off the hydraulic pump.
- The flight crew possessed only a basic understanding of the aircraft's hydraulic system limitations.
- Maintenance errors included failing to record or properly action known defects in the technical log.
- The flight data recorder was non-functional due to an unaddressed internal fault in the acquisition unit.
- The underwater locator beacon had been removed months before the event and was not replaced.