Footage from a rollercoaster ride moments before a teenager fell to her death suggests a safety bar had not been lowered, an inquest has heard.
A safety expert also said that aspects of restraints on the hydro ride at Oakwood theme park were "unacceptable".
Hayley Williams, 16, of Pontypool, was on holiday in west Wales when she fell 120ft to her death in April 2004.
Her sister had told Haverfordwest Coroner's Court that no safety checks were made as they queued for the ride.
The jury were shown frames from a recording of Hayley boarding the ride. She was wearing a yellow plastic poncho to protect her from getting wet as the boat dropped down a near-vertical chute into a plunge pool at 50 mph.
Hayley, a Sunday school teacher and talented musician, was sitting in an outside seat on the last-but-one row to the rear.
Hayley was dressed in a yellow plastic poncho as she boarded
Pembrokeshire Coroner Michael Howells had said the G-force as the boat plunged down, would have been capable of flipping out anyone who was not secured.
Hayley's sister Hannah Williams previously told the court that by the time the carriage climbed to the top of the ride her eyes were closed from fear. As it began to descend, she recalled one of her friends crying out that Hayley had fallen.
Image expert Andy Laws - who analysed footage taken on the day Hayley died and staged a reconstruction - said the image of Hayley was consistent with the T-shaped safety bar on the seat being left "open," leaving her unsafe.
He was also asked to examine whether the female ride assistant had physically checked to ensure Hayley was secure.
He said: "The female stood adjacent to Hayley for a total period of around 23 seconds but during that time there was no appearance that she carried out any physical checks on the belt or the T-bar."
Ride assistant Rebecca Chittleburgh, 21, subsequently gave evidence. She said she knew from the operating manual that she had to physically check safety features were secure but that she had been distracted.
She said she then saw the carriage pull off and she had not given the signal to activate the ride.
The jury also heard from mechanical engineer Roger Jones who considered safety to be "unacceptable".
He manually tested all 24 bars and belts and thought they were operating as they should. But, he revealed, he was able to get out of Hayley's seat unaided even after pulling the security lap bar down into place.
"I sat in the seat, pulled the bar towards me and I found that I could get out," he told the inquest. "You are actually able to get out of it," he added.
'Undo safety belt'
Mr Jones, who is now retired, acknowledged that if the seat belt and the lap bar were both being used, a passenger would be secure.
But, he added, he had discovered it was possible to undo the safety belt even once a lap bar was in place and that this could not be detected by a ride supervisor, either visually or by physically trying it.
"You need the lap belt just in case something goes wrong with the lap bar," he said.
"The foreseeable risk in my opinion is such that the reliance on this system has proved to be unacceptable."
Senior management from Oakwood are expected to give evidence soon.
The inquest continues.