Mystery surrounds what caused a sea plane piloted by Peter Lynch, 52, and occupied by his girlfriend Endah Cakrawati, 30, to plunge into Perth’s Swan River during Australia Day celebrations, killing them both.

The crash, caught on film by several onlookers, forced the cancellation of Perth’s annual sky show and has triggered an investigation by the Australian Transport and Aviation Safety Bureau.

The tail of the plane was retrieved from the river on Friday, and authorities said the operation to salvage the remainder of the wreckage would be completed on Saturday.

Endah Cakrawait tragically died with her partner, Mr Lynch, in the crash. Photo: ABC/Halden Boyd

The flight over Swan River was a scheduled air display as part of the Australia Day festivities. The Civil Aviation Safety Authority has revealed the plane was not cleared to fly below 500 feet during the display.

The pilot, Mr Lynch, had been planning to open a new aviation museum at Evans Head on the northern New South Wales coast, and an aviation park.

In a 2013 interview, he said it was his childhood dream to be a pilot.

“The most enjoyable aspect of flying is the pure pleasure of getting up in the sky and having the freedom to go virtually anywhere,” he told Down Under Aviation News.

Mr Lynch was a mining consultant with business interests in Indonesia, and only moved to Western Australia from Queensland six months ago.

The father-of-three’s former partner, Laura, posted on Facebook: “With great difficulty, I am unbearably saddened to confirm that my great friend and the father of my children passed after a tragic accident.”

Mr Lynch’s girlfriend, Ms Cakrawati, worked with him as the investor and public relations manager for Cokal, an Australian-listed coal company which operates in Indonesia, Tanzania and Mozambique.

She is known as a model, MC, and presenter in Indonesia.

The Indonesian Consulate General said they had contacted Ms Cakrawati’s family, offering to bring them to Perth, Indonesian Consulate General Ade Padmo Sarwono told the ABC.

According to her Linkedin profile, she studied at Universitas Esa Ungul in Jakarta, and had worked for Cokal for three years.

Just six months ago, around the time Mr Lynch moved to Perth, Ms Cakrawati wrote on her Facebook page: “I have a great life, great friends, and great LOVE…..JUST PERFECT.”

Thousands of onlookers gathered in Perth for the annual sky show watched in horror as the Grumman G-73 Mallard flying boat banked sharply before crashing into the water.

#Plane crashes into the Swan River. Horrible sight. Filmed by Mark Annett-Stuart. #AustraliaDay #Perth pic.twitter.com/MPI5wRSxeO

— Jorden Teo (@JordenTeo) January 26, 2017

WA Police Acting Commissioner Stephen Brown was doing a television interview from the South Perth foreshore as the tragedy unfolded.

“I heard a change in the tone of the aeroplane that was above my head and the people in front of me were clearly distracted,” he told reporters.

“I turned … to see the plane had crashed, that it clearly had broken at least in two significant parts and was sinking very quickly.”

He said emergency services were on the scene within minutes of the crash.

Lloyd Douglas, who was on a nearby boat when the plane smashed into the water, told the ABC that witnesses rushed to the plane and climbed onto its wings shortly after the crash in a failed attempt to rescue the couple.

‘It didn’t seem real’

“People were very quickly on the scene, divers in the water within minutes, but tragically those gallant efforts failed in their attempts to save these two people who tragically lost their lives,” he said.

Perth Lord Mayor Lisa Scaffidi said the Skyworks event would undergo a review.

“I think it’s an appropriate time to consider all operational aspects of such an event, particularly aerial flights and the like,” Ms Scaffidi said.

However she expected the Skyworks show would continue to be held in future years.

“Skyworks is an established part of the West Australian community’s celebration of Australia Day,” she said.

Please help the ATSB by sharing your photos or videos of the Australia Day air crash through their channels. https://t.co/6u1aWYV4oC

— WA Police Force (@WA_Police) January 27, 2017

The Australian Transport Safety Bureau (ATSB) has sent two investigators to probe the cause of the crash, but, in a statement, said those complex investigations could take up to 12 months to complete.

Witness Tamara Legenstein told the ABC she first saw the plane out of the corner of her eye.

A horrified onlooker captured the moment before the plane hit the water. Photo: Michael Legg/ABC

“I saw it heading towards the water, I was sort of thinking at first that it was a stunt plane and that it was going to go down low and then head up back into the sky,” she said.

“But it started to cartwheel, hit the water and then broke into two. [It] took a few seconds to realise that it was real.”

https://www.youtube.com/watch?v=ipldhzONnH0

Peta Healy told the ABC people around her were initially in disbelief, before hoping that those in the plane were OK.

“I watched the plane come down the South Perth side of the river and turn, and as it turned it went on its side and headed to the water.

“So it nosedived, and then I head a ‘boof’, like a noise, and you could see that it was broken into two pieces.

– with ABC