A coach driver suffered an “event” at the wheel before a motorway crash that killed him and a 15-year-old schoolgirl last week, an inquest heard.
Stephen Shrimpton, 40, died in the M53 crash in the Wirral along with school pupil Jessica Baker.
The schoolgirl suffered "instantaneous" death from "catastrophic" injuries in the crash near junction five at Hooton on the Wirral on Friday, September 29.
She was partially ejected from the school bus which landed on her, Liverpool Coroner’s Court was told.
Mr Shrimpton was driving the coach taking pupils to two local schools, West Kirby Grammar School and Calday Grange Grammar School.
Andre Rebello, senior coroner for Liverpool and the Wirral, said CCTV footage from inside the coach showed Mr Shrimpton slump to his left while driving the coach, which at the same time left the carriageway and went up an embankment before ending up on its side.
Jessica, from Chester, was a passenger along with around 50 other youngsters on the bus taking her to West Kirby Grammar School where she was a Year 11 pupil.
Mr Rebello said it was "miraculous" no one else was killed as he gave brief details of the incident during the opening and adjourning of the inquests into the deaths of Jessica and Mr Shrimpton at Liverpool Coroner's Court.
The coroner also said "clarity" was needed from the government around the wearing of seat-belts on coaches and buses.
Mr Rebello said though further medical examination results are to come, the most likely cause of death for Jessica will remain a severe head injury.
Mr Rebello said: "At approximately 8.03am the road traffic incident occurred and the coach, travelling north bound, collided with the embankment on the nearside and the coach came down on its side, causing fatal injury, life-changing injury and serious injury and lots of minor injuries.
"Given the extent of the collision it is miraculous that there were not more fatalities.
"The court has been briefed by the road collision unit investigation and the CCTV footage within the coach.
"It is fairly evident that the driver has suffered an event whereby he is seen to slump to his left side and it is at this time that the vehicle leaves the carriageway."
Mr Rebello said the exact circumstances of how Jessica was killed will depend on the ongoing police investigation.
He added: "However it would appear she was partially ejected from the vehicle and it appears the vehicle has landed on her causing catastrophic, certainly instantaneous fatal head injuries."
Mr Rebello said further medical examinations will be needed to establish Mr Shrimpton's cause of death with focus on the examination of the condition of his heart.
The inquest hearing was told Mr Shrimpton was pronounced dead at the scene at 8.50am and formally identified by his wife Tania Shrimpton.
Jessica was also pronounced dead at the roadside at 9.01am, and identified by her father, a nurse, Mr Shaun Baker.
Mr Rebello added that anyone over the age of 14 is responsible themselves by law for wearing a seat belt.
But he said clarity was needed over the rules for coaches.
He added: "I am old enough to remember the Tufty Club and the Green Cross Code and the public information films about, 'Clunk Click every trip'.
"And clearly, because I am now considered very old, I suspect there are generations who have never seen these public information films and may not be fully aware that the chances of severe injury or fatal injury are so much reduced by wearing of a seat belt."
Mr Rebello said he intends to write to the Department of Transport for clarity on the law for seat belts on school-run buses and coaches.
After the crash, four other children were taken to hospital including a 14-year-old boy whose injuries are said to be "life-changing", according to Merseyside Police.
Others were handled at an emergency training centre, with 13 treated for minor injuries before they were released.
A full inquest will be heard on March 20 next year.
