A Perth train on which the brakes failed twice last month is back in service without the cause of the problem being identified.
The train's driver had to use the emergency brakes as it pulled into Kenwick station on the Armadale line at 7.42pm on November 7.
Passengers were moved to another train and the railcar was taken to the Claisebrook depot.
Public Transport Authority spokesman David Hynes said the railcar was tested thoroughly but the cause of the fault could not be found.
Mr Hynes said the railcar returned to service on Friday, December 6. But the end of the railcar involved in the incident will not be used.
Another driver reported a similar incident on the same railcar on November 1.
"The cause of the fault has not yet been determined definitively," Mr Hynes said.
"As a result we have sought external expert input and a full investigation into the brake control circuit is currently being undertaken.
"The fault appears to be an isolated incident.
"If a clear issue can be identified it will immediately be fixed."
Shadow transport minister Ken Travers said, at the very least, the PTA should have warned all drivers about the problem so they could be on the lookout for similar issues.
"It all comes down to the fact that - with budget cuts and the lack of railcars - the PTA is under real pressure to keep as many railcars operating as possible," he said. "But this should not be done at the expense of normal safety procedures."
Mr Hynes said the A-series trains had operated safely on the Perth network for about 23 years.
"In addition, Transperth is the only urban rail network in Australia to operate an automatic train protection system," he said.
"This system automatically applies the brakes if a train travels above the allowable track speed past a signal and also applies the brake automatically if a train is going to pass a red signal.
"This extra layer of protection makes our trains and braking systems safer than any other in the country."