An experienced bus driver has had a conviction of causing death by negligent driving overturned because of a lack of evidence around how hard she braked.
A 42-year-old man and his two-year-old daughter died in a crash between their sedan and the school bus south of Hobart in August 2020.
Christine Helen Chatterton was handed a three-month suspended sentence in 2022 after being found guilty of two counts of causing death by negligent driving.
A magistrate ruled she applied excessive brake pressure on a sweeping bend, which caused the bus wheels to lock before it skidded into an oncoming lane.
Ms Chatterton appealed the guilty ruling on several grounds, including that there was no evidence about her degree of brake force.
In a judgment published on Thursday, Acting Justice Brian Martin set aside the conviction and sentence, recording a not guilty verdict.
Justice Martin said there was no doubt braking caused the wheels to lock.
"However, there was no evidence as to the amount of brake pedal force required to lock the wheels," he said.
"All that was known was the amount of force applied by (Ms Chatterton) caused the wheels to lock."
Justice Martin said the fact the wheels locked did not prove the force was excessive.
He noted if the bus, which was manufactured in 1998, had been fitted with an ABS braking system the wheels would not have locked.
Justice Martin said Ms Chatterton wasn't informed the bus didn't have ABS and from her perspective she was driving a relatively modern vehicle.
There was no evidence a "reasonably prudent" driver would have known there was a risk of the wheels locking when braking, he said.
Hobart Magistrates Court was previously told Ms Chatterton had been significantly impacted by the crash and had relinquished her bus licence.
There were no students on the bus at the time of the crash.