The independent inquiry into the Navan bus crash in which five teenage girls were killed, has found that the anti-lock braking system on the school bus was disabled.
Five teenage girls were killed and 46 children were injured when the bus overturned as it was taking youngsters home from school in Navan, Co Meath last May.
As thousands of children prepare to return to classrooms tomorrow, tests carried out on seven other Bus Éireann school buses found that all had anti-lock brakes (ABS) which were disabled.
The ABS system is designed to prevent the brakes from jamming in the event of an emergency and helps a vehicle to stay on the road.
The Press Association has learned that two school buses and five public buses were examined at Dublin Bus's Broadstone Depot as part of the inquiries into the Navan bus crash.
All seven vehicles failed the test for a working ABS system.
Bus Éireann has now hired a private contractor to examine its ABS systems. A company spokeswoman said she was not aware of this or of the tests that were carried out on the seven buses.
She said she could not comment about the bus at the centre of the Navan investigation.
"But I can guarantee you that where it (ABS) is fitted in buses in service, it is operational," she said.
The spokeswoman said there was no legal requirement for buses to have ABS brakes but added there was a careful maintenance system for those that had them.
"If ABS was found not to have been functioning on a bus, it would immediately been brought in for service," she said.
The independent Navan bus crash inquiry team, which is headed by former assistant Garda commissioner Jim McHugh, has requested more time to complete its investigation.
Bus Éireann said Mr McHugh had asked for the date to be extended two weeks ago because the investigation was taking longer than envisaged.
The report is now expected to be published at the end of September. Two separate investigations into the crash by gardaí and the Health and Safety Authority are continuing.
A Garda spokeswoman said she could not comment while their investigation was continuing, while the Health and Safety Authority also refused to comment.
The road outside Navan was in the process of being resurfaced and temporary traffic lights were in place when the bus was involved in an accident with two other cars.
PA