FROM the emergency response to a fatal plane crash to the days of combing through the wreckage that followed, an Agnes Water man witnessed it all.

1770 LARC owner Neil Mergard offered his amphibious boat to help access the remote location where the 1770 Castaway plane ploughed into a beach at Middle Island.

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The crash on Tuesday left a 29-year-old United Kingdom woman dead and three others seriously injured.

His boat, which has land and sea capabilities, was used to take Australian Transport Safety Bureau investigators to the scene on Wednesday and Thursday.

On Thursday Mr Mergard watched as the engine was cut out of the plane, a key part of the investigation.

"(The investigators) are very thorough, I'll give them that much," he said.

Two investigators and Agnes Water State Emergency Service volunteers combed the beach area looking for clues as to what caused the crash.

Agnes Water pilot Les 'Woody' Woodall was flying the plane when it went down, citing "engine failure" as the cause when he spoke to witnesses.

Mr Mergard found it difficult to put into words the scene as they arrived.

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"It was a pretty shocking scene," he said.

A rescue helicopter had landed nearby the wreckage and paramedics were already working to stabilise all four passengers.

But one woman, a 29-year-old from United Kingdom died on the scene.

The tourism operator had a unique look into a government-body investigation during the two days he spent at Middle Island with the ATSB.

It's the 122nd time the LARC, which is listed as an Agnes Water SES asset, has been used for an emergency response.

Mr Mergard said he had been involved in rescues at the mostly-inaccessible beach land at Middle Island before.

"It's a pretty sad state of affairs," he said. "It gives you a sense of relief though when you have that sort of support around you with the emergency services.

"It's great everyone's also rallying around Bruce (Rhoades) and the business."

The plane crashed with four people on board, including pilot Woody, a UK woman (now dead), a 13-year-old boy and a 21-year-old woman from Ireland.

Mr Mergard said despite the tragic details of the event, it showed how united the small township was.

"I love our community, how solid it is," he said. "Everyone is so loving and compassionate spirit."

The ATSB spent their last day on site on Thursday, the investigation is ongoing.