The Australian Transport Safety Bureau (ATSB) expects to deliver its findings on a helicopter collision that killed four people on the Gold Coast between July and September in 2024.

“A final report will be released at the conclusion of the investigation. Should a critical safety issue be identified during the investigation, the ATSB will immediately notify relevant parties, so that appropriate safety action can be taken,” the bureau’s website said.

The Australian National Audit Office 2019 report into the bureau’s investigative efficiency found that it took an average of 19 months to produce a report on “complex” incidents.

ATSB Chief Commissioner Angus Mitchell has previously said that transport safety investigators with experience in helicopter operations, maintenance and survivability engineering had been deployed to the crash site from the bureau’s Brisbane and Canberra offices.

Also on Friday the mother of a young boy who was critically injured in the crash thanked online cash donors for their “amazing” generosity.

Winnie De Silva, 33, from Geelong, and her son Leon, nine, were rushed to hospital on Monday after their sightseeing chopper collided with another machine near Sea World and plunged onto a sandbar.

Four people died in the first machine and another young boy was critically injured, while four passengers and the pilot of the second helicopter were injured by flying glass shrapnel when its windshield shattered.

A Queensland Health spokesperson said Nicholas Tadros, aged 10, from Sydney was in an “unchanged” condition from Thursday when he was listed as being in a critical condition and in an induced coma.

His mother Vanessa Tadros, 36, Britons Ron and Diane Hughes, 65 and 57, and 40-year-old pilot Ashley Jenkinson died at the scene on Monday.

An online fundraiser for the De Silva family, set up by Winnie’s husband Neil, has brought in almost $60,000 as of Friday.

Ms De Silva, who is in a stable condition at Gold Coast University Hospital, released a statement on Friday about Leon’s recovery at the Queensland Children’s Hospital in Brisbane where he is in a stable condition.

“We are so grateful for the generous contributions to the Go Fund Me page. The generosity of people has been amazing, and I can’t thank you enough,” Ms De Silva said.

“More importantly, I continue to pray for the recovery of young Nicholas, who was seated near me in the helicopter, and offer my heartfelt condolences to the families of the other passengers. It is an unthinkable and difficult time for us all.”

More than 1300 donors contributed to the De Silva fundraiser, with dozens of people pledging amounts between $200 and $700 in the space of three days.

A separate fundraiser for Nicholas has received more than $48,500 over two days with one of the largest individual donors opting to remain anonymous.