The impact of the Smiler rollercoaster crash that left five passengers with life-changing injuries was similar to a 90mph car accident, a court has heard.
Alton Towers operator Merlin Attractions Operations Ltd has been told it is facing a fine that could top £10 million after admitting a health and safety breach on the 14-loop ride.
Vicky Balch, then 19, and Leah Washington, then 17, who each lost a leg in the crash in June last year and several other people who were trapped for hours attended Stafford Crown Court on Monday for the sentencing hearing.
Prosecuting, Bernard Thorogood told the court that the passengers on the £18 million ride watched with "disbelief and horror" as they realised they were going to collide with an empty carriage.
He said the kinetic energy involved in the crash on June 2 2015 was equivalent to "a family car of 1.5 tonnes having collided at about 90mph".
Opening the case, Mr Thorogood said the test carriage had been sent around the ride but had come to rest in a valley of the track, unseen by ride staff.
The engineers had overriden a computer system that they believed had halted the ride in error - and sent a full car along the track into the path of the empty carriage.
"The subsequent collision was plain to see to some in the train, and I refer to those in the front row's statements, where they speak of their disbelief and horror as they saw ahead up the track the train into which there were going to dive," he said.
The court was told the victims of the crash were held at a "very difficult angle", around 20ft above ground, waiting for medical attention because of the inaccessibility of that part of the ride after the two trains on the ride "meshed together".
Mr Thorogood said that while the mistakes that led to the crash were made by individuals, the ultimate responsibility lies with their employers.
In its investigation, the Health and Safety Executive found that a "near-gale" may have been to blame for the empty carriage failing to clear the Cobra Loop in the first place, following an early problem with one of the ride's lifts.
Mr Thorogood said: "One empty train was sent to establish the lift was operating normally but, unknown to those present, this train failed to clear the loop - with which this case is unfortunately and sadly concerned.
"The problem was the head-wind, which that train could not overcome."
The Smiler ride itself, it was concluded, was "well-designed", as were the computer and "sophisticated" control systems, while the operator of the ride had followed safe working practices.
It concluded that the defendant, Merlin, fell "far short" when it came to governing the inevitable need for engineers from the park's technical service's department to fix faults on the ride.
However, he added that there was "absolutely no evidence of a task analysis-based approach for engineering work, in particular in dealing with ride faults".
Mr Thorogood, summing up that point, said "engineers revealed a range of understandings of important aspects, which with a single system (of working) there would not be".
Giving an example of the idiosyncratic approach, Mr Thorogood said one engineer who worked on the Smiler that day told investigators after the crash that he had "assumed" the rollercoaster had been fitted with a type of safety trip-switch present on at least one other park ride, when in fact it had not.
He went on to say there were "various states of knowledge" of the fault alarm systems on the ride.
He said: "The staff had come to distrust at that stage the fault signal on occasions and hence they thought that the one that was showing was an error.
"There was nobody, no individual who had to sign off and take responsibility for that event."
At the beginning of Monday's hearing, the Recorder of Stafford, Judge Michael Chambers QC, said: "One of the features is not just the impact on those injured, but on those close to them."
A court hearing in April this year was told that Merlin had carried its own internal investigation following the incident, which established that a worker manually overrode the rollercoaster's governing computer system.
Alton Towers has instituted 30 changes following the crash to improve safety of the ride, the court heard.
Speaking about the potential fine to Merlin, Mr Thorogood said it might be anywhere between £3,000 and £10 million, but could be increased even higher.
Press Association
