By Matangi Tonga reporters

Hydraulics complications occurred mid-flight, before the Lulutai Airlines Saab 340B lost control while taxiing, after landing at Fua'amotu with a full load of passengers in December last year. Hydraulic fuel loss and other safety problems with the aircraft are detailed by aviation safety investigators in a preliminary report [2] published in April.

It provides factual information derived from the investigation's initial evidence collection phase. Among those findings are:

• The source of the hydraulic leak has not been identified because of damage to the undercarriage in the accident sequence, when it hit a concrete bund area near the Fua'amotu domestic terminal;

• The aircraft had no brakes as it approached the domestic terminal;

• The Flight Data Recorder had no input data from the flight;

• Indications were that, “a deliberate action to disable the [flight recorder] system had been taken”;

• The Cockpit Voice Recorder was working but inaudible due to an external source;

• There was no Underwater Locator Beacon attached to the cockpit recorder.

On 8 December at about 1306 the aircraft, on a scheduled domestic flight with three crew and 35 passengers, aborted their descent into Vava'u and returned to Tongatapu after the flight crew considered there was a potential hydraulic leak However, no warning lights were illuminated on the cockpit master caution control panel.

The Flight officer would be required to operate the pump handle for the emergency hydraulic system to extend the landing gear in order to land at Fua'amotu International Airport. The crew discussed a flapless landing and notified Air Traffic Control. The crew tried contacting their company, Lulutai Airlines Ltd., to organise towing “however they did not receive a response.”

Air Traffic Control notified the Rescue and Fire Service of a local standby for A3-PUA.

Full emergency response

The Rescue and Fire Service treated it as a full emergency response. Key stakeholders including the hospital were notified, and His Majesty’s Armed Forces (HMAF), were on stand-by.

The crew commenced their descent from about 54 NM from the airport. The crew discussed use of the emergency hydraulic pump, then selected the landing gear to 'down' The nosewheel locked down, followed by the right undercarriage leg. The flight officer then pumped the emergency hydraulic system pump about 8-10 times,  and the left undercarriage leg locked down. The landing checklist was then carried out.

The captain and flight officer discussed whether they would attempt taxiing the aircraft after landing and agreed they would decide after landing. They called their company to arrange towing and engineering support.

After the Air Traffic Control cleared the aircraft to land on approach, the crew tried to lower the flaps, however the flaps did not move.

Safe landing

The aircraft landed safely at about 1357. The crew was able to taxi the aircraft along runway 35, and then taxiway 'Alpha' onto the domestic terminal apron.

“As they approached the terminal, and before commencing their final right turn, the captain identified that they had no brakes, and the aircraft departed the taxiway.

Undercarriage collapsed

“The crew shut down the engines shortly before the right undercarriage leg impacted a disused concrete bund area, that was part of a previous refueling installation, at about 1400. The aircraft veered to the right, and the right undercarriage collapsed.”

The main exit on the forward left side of the cabin could not be used because the aircraft was tilting to the right. Passengers were evacuated through the emergency exit with the assistance of the Fire services and HMAF who were on standby.

There were no reported injuries.

Flight Data Recorder

The Tonga Civil aviation Authority reported that following the incident the flight data recorder (FDR) and cockpit voice recorder (CVR) were removed from the aircraft and were quarantined by the operator at their head office. They were delivered to Australian Transport Safety Bureau (ATSB) investigators by the operator at the aircraft on 21 December 2023, when a download was then carried out. A comparison of the flight logs indicated that the last correctly recorded flight on the FDR was on 11 July 2023.

The Cockpit Voice Recorder was recovered from the operator and taken to Canberra to be examined by Australian Transport Safety Bureau inspectors, assigned as an accredited representative to the Tonga Chief Investigator, Mr James Panuve.

The Tonga Chief Investigator and ATSB investigators visited the accident site for a detailed visual examination of the aircraft on 20 December 2023. They revisited the aircraft on 14 February 2024 to conduct a further examination to identify the source of the hydraulic leak. Leaks were identified from damage likely associated with the damage in the accident sequence.

To date, the investigators have interviewed the flight crew and maintenance personnel, examined the aircraft, reviewed the technical and flight logs, and downloaded the CVR. They published the preliminary report as an update on the investigation. It provides no analysis or conclusions.

“The investigation is continuing and will include further review and examination of: the recorded CVR data, the aircraft electrical system for the FDR the aircraft maintenance documentation, ” they stated.

A final report will be released at the conclusion of the investigation.

The SAAB 3408 is a low-wing, pressurised regional commuter aircraft, fitted with two General Electric (GE) CT7-98 turboprop engines.

A3-PUA, serial number 408, was manufactured in Sweden in 1996, and first registered in Tonga in April 2016. It was first registered with Lulutai Airlines Limited in September 2020. The captain and first officer joined Lulutai Airlines in September 2020 and held valid licences at the time of the incident.

At the time of the occurrence, the airframe had accumulated 39,094.5 hours total time in service.

The investigation is supported by financial assistance from the Australian Government represented by the Department of Foreign Affairs & Trade of Australia (DFAT).

Lulutai Airlines Ltd. is owned by the Tonga Government and the Retirement Fund Board. The Chairman of the airline's Board is the Prime Minister Hon. Hu'akavameiliku.

Links:

Friday, December 8, 2023 - 19:09: Passengers screaming, Lulutai flight slides off taxiway at Fua'amotu, after Vava'u landing aborted [3]

Tuesday, December 12, 2023: Tonga Civil Aviation Authority investigating Saab 340 incident [4]

Saturday, January 6, 2024: Air accident investigation ongoing as Lulutai Airlines has difficulty replacing aircraft [5]