Control of a Bell 204 helicopter was lost during water uplift due to the cables attaching its firefighting bucket being captured over its left rear skid, creating a shift in the centre of gravity.
The helicopter had been tasked on firefighting operations on the afternoon of 20 September 2023 when it approached the dam on a property at Tarome, in Queensland's south-east, the final report from the ATSB's investigation into the accident details.
"The cables attaching the Bambi Bucket to the helicopter had been caught over the left rear skid by the time the helicopter was on approach to the dam and when it was uplifting water into the bucket," said ATSB Director Transport Safety Kerri Hughes.
"As a result, due to the tethered weight over the left rear skid, when the pilot began lifting the bucket from the dam, the helicopter's centre of gravity moved aft and left. This created asymmetric lift loads, resulting in the helicopter's loss of control."
The helicopter struck the water, and the pilot reported that it became inverted almost immediately, filled with water, and began sinking to the bottom of the dam.
The pilot initially tried escaping the sinking helicopter via the front left door. Unable to open it, they swam to the rear of cabin, by which stage the helicopter was almost fully submerged. Following attempts to open the rear right door and kicking out the windows, they escaped by opening the left rear door after applying considerable force.
"The pilot had undertaken HUET - helicopter underwater escape training - about 2.5 years prior to the accident, which increased their chances of survival when the helicopter submerged in the dam," Ms Hughes said.
"Helicopters tend to be 'top heavy', thanks to their engine/s, transmission and main rotor system being above the cabin, and so can flip over quickly once hitting water. As such, this accident reinforces just how important conducting HUET is to increasing helicopter occupants' chances of survival in the event of impact with water."
The accident also emphasises the complex nature of conducting external load operations over water, where research has shown that the risk of an accident involving a firefighting helicopter is twice as high as private helicopter operations.
"There can be a lack of visual references, visual illusions over water, limited visibility and vertical reference of the hook and external load through mirrors and bubble windows, which all add complexity when operating helicopters with external loads over water," Ms Hughes said.
"Fouling of external load suspension cables on the airframe can lead to rapid changes in weight distribution, asymmetric lift and loss of control.
"As Australia moves into another fire season, this accident investigation highlights how correct cable positioning is vital to the safety of external lift operations."
You can find here the report: Collision with water involving Bell Helicopter Co 204B, VH-EQW, Tarome, Queensland, on 20 September 2023
Watch this ATSB safety promotion video detailing the importance of HUET:
https://youtu.be/uErwySkqqGw?si=cKSh6pUMVi6rJWZ6
