Accident investigators are slated to deliberate a final report into the ditching of a rescue helicopter off Auckland Islands in 2019 this November.

Southern Lakes Helicopter's Kawasaki BK-117 helicopter was reported missing near the sub-Antarctic islands, about 465km south of Bluff, on the evening April 22, 2019, while on a mission to transfer a sick seaman from an ocean trawler.

Pilot Andrew Hefford, winchman Lester Stevens and medic John Lambeth were all onboard and feared lost.

But all had survived the accident and, wearing immersion suits and life jackets, had made it ashore on Enderby Island, the main island of the remote archipelago.

They were found on its beach the next morning by their boss Sir Richard 'Hannibal' Hayes, who landed and rescued them.

Three years on from the incident, the Transport Accident Investigation Commission (TAIC) has yet to publish its findings.

TAIC senior communications advisor Simon Pleasants tells the Southland App that's not unusual, however.

"As usual, the Commission is taking the time necessary to produce reports that the whole sector can rely on," he says.

"The Commission’s inquiries are not fault-finding; we very specifically never blame anyone. The Commission inquires to establish how people working in the sector can best avoid a similar accident.

"If I remember correctly, the Commission’s inquiries into accidents at Lochy River, Mt Alta, and Fox Glacier all took 3+ years."

The Commission is a quasi-judicial body occupying a position in the New Zealand justice system similar to the Coroner or a District Court.

But, it is inquisitorial rather than accusatorial.

"So, it takes very seriously its duty to observe natural justice for the people who are likely to be directly affected by what the report says," Pleasants says.

"We consult and listen and may go through more than one draft final report before the Commission is satisfied with the result.

"During the process of an inquiry, it’s not uncommon for investigators to head down lines of inquiry that do not live up to their initial apparent promise."

The Commission is currently due to deliberate in the final report at its November meeting.

If they approve the report for publication, that's likely to happen around the end of January 2023.

The timeline could change though, Pleasants says.

Hefford told Stuff at the time the impact with the water had been "violent" but none of the men could say much more about the crash itself while the investigation is ongoing.

Stevens had been knocked unconscious and was pulled from the helicopter by Hefford and Lamberth. Stevens suffered torn ligaments, a broken nose and bruising, while Lambeth fractured a rib.

The three men swam to shore and spent a cold night on the island, unable to signal for help as their locator beacons were lost in the crash.

The helicopter had floated for about two minutes, before sinking in 12 metres of water. It was salvaged and examined in May 2019.