Transportation authorities found a 10-centimeter crack on the undercarriage of a train car belonging to Osaka-based Nankai Electric Railway Co. on Tuesday, following the discovery of a similar 14-cm crack on the undercarriage of a train of the same model on Saturday.
The authorities also launched a probe into how the airport express trains went into service despite the cracks, deeming it a "serious incident" that could have led to an accident.
The 14-cm crack was discovered under a limited express "rapi:t" service train. Two investigators from the Japan Transport Safety Board held hearings at Nankai Electric Railway's office on Tuesday.
The railway operator found a similar-sized crack on a third train car of the same type in April.
It said it would continue operating the remaining four trains of the type for the rest of the day.
A conductor was the first to notice a problem on one of the trains, detecting an abnormal sound coming from the coupling between the second and third carriages of the six-car passenger train while it was traveling from Namba Station to Kansai International Airport on Friday afternoon.
An attendant checked the train at the time, but it completed its service for the day before further inspections were conducted at a depot in Osaka, where the crack was then discovered near the motor on the undercarriage of the second car.
The train in question was built in 1994, according to the operator.
