Scott Hamilton, who was driving a Stirling Council recycling lorry, failed to check that it was clear behind him before backing to let another vehicle pass.
Hamilton, 44, had to manoeuvre to give the car space to get by on a single track road at Sheriffmuir, above Dunblane, Perthshire.
He asked his colleague, Lee McEwan, to check the nearside mirror - but neither of them that noticed that retired teacher Peter Wills, who used his scooter daily to watch wildlife and red kites near his home on Sheriffmuir, was behind them.
The 7.5 tonne truck collided with Mr Wills’ 4-miles-per-hour runabout with a “thud”.
The impact caused massive injuries that stopped him breathing and led to his death in minutes.
Hamilton, of Bonnybridge, Stirlingshire, had denied causing the elderly man’s death by dangerous driving.
But today on the second day of his trial at the High Court in Stirling before Lord Ericht, the Crown accepted his plea of guilty to the lesser offence of causing death by careless driving.
Sentence was deferred until a sitting of the High Court in Stirling on October 25, and he was banned from driving immediately. The offence carries a maximum penalty of five years’ imprisonment.
Advocate depute Jane Farquharson said the original charge - which had alleged Hamilton had been “provided” with a trained reversing assistant but did not use him - made clear the basis on which the allegation of dangerous driving had been levelled.
But she said as Mr McEwan gave evidence, it emerged that his position was “less certain”.
Mr McEwan, 18 at the time, said that he was not detailed to be a reversing assistant, or “banksman” on Hamilton’s lorry, which he claimed was not required to have a banksman because it was smaller than the council’s normal recycling vehicles.
He insisted he was only on board to empty recycling boxes, and was “just an apprentice”.
Miss Farquharson said: “As a result I have taken the view that the responsible course of action is to accept the plea offered.”
She added that although Mr Wills was not wearing a lap belt on his scooter, the result of that had simply been that he had been flung backwards by the impact of the lorry, rather than being dragged underneath it.
She said his fatal injuries - to the chest and neck - were caused by the impact itself, and the fact he was not wearing a belt had made no difference to the outcome.
She said: “His life-ending injuries were sustained as a direct result of the impact with the rear of the refuse lorry as it reversed backwards.”
Investigators had found furrows on the tarmac which indicated the wheelchair had been pushed backwards for three-quarters of a metre, before it was pushed over snapping its rear offside wheel clean off at the hub.
They checked the view Hamilton would have had at the time.
They found the rear view was restricted by the width of the vehicle and the height of its storage bins, and the view from the door mirrors was “further compromised” by the fact that the back of the lorry was facing slightly uphill, so Mr Wills would have been completely in the driver’s blind spot.
She said Hamilton had received “appropriate training”, and had signed off training documents only nine months earlier confirming he was aware of the dangers of reversing, and what safety measures to take.
She said: “His plea of guilty acknowledges that he failed to implement them.”
She added that the documents signed off by Hamilton advised drivers should “reduce reversing manoeuvres wherever possible, only reverse when safe to do so, and exercise extreme caution”.
During the trial, Mr McEwan recalled the incident.
He said: “Scott just says if I could see anything in my mirror and I said ‘no’ and he put the motor into reverse.
“It was just a split second thing.
“We assumed there was nothing there.
“We went back a few yards and then we heard the thud.”
He said he had seen Mr Wills on his scooter earlier, and the fact they they had hit him was “the first thing that came into my head”.
He found the electric scooter lodged between two beams at the back of the lorry, and Mr Wills on the road, with “blood gushing out of his head”.
He phoned 999, and Hamilton gave Mr Wills CPR until the emergency services arrived.
Paramedics found Mr Wills unconscious and with no pulse.
Doctors arrived by police helicopter, and he was pronounced dead at 10.42 on the day of the incident, December 3rd 2014, about 45 minutes after the collision.
The driver of the car which had been waiting to pass, Iain Dick, 60, said that at the point where he met the lorry, it was much easier for the lorry to reverse than it would have been for him.
He said: “I could sense that there could be a little bit of frustration that I was there.”
The lorry went back about two metres, and he heard a “grating sound” and initially thought it had hit a bin.
He then realised something serious had happened, went round the back of the lorry himself, and saw Mr Wills.
Hamilton was crying and said words to the effect of “I didn’t see him, I didn’t see him”.
Mr Wills’ widow Viriginia told the jury that her 50-year marriage to Mr Wills had been “paradise”.
She said her husband had been left paralysed down one side and without speech after a stroke eight years before his death, but was still “more like a man of 60 than 80”.
Mrs Wills, now 80 herself, a mother of three and a grandmother, said Mr Wills “revelled in his independence” and would spend up to two hours every day out on his electric scooter near their isolated home “high in the hills” above Dunblane.
She said she sometimes “ran beside him” but on the morning of the incident she had stayed at home to saw logs to get a fire going for his return when she noticed a helicopter flying low above their home and became worried.
She said she “jumped in her car” to see what was happening, and came across a policeman.
The court heard that since the tragedy, Stirling Council recycling lorries had been fitted with sensors to warn their drivers of obstacles behind them.
Hamilton refused to comment after the case.