Train crew members were unable to communicate via radio in the moments after a suicidal dad threw himself in front of an oncoming train with his 5-year-old daughter in his arms, The Post has learned.

An internal New York City Transit report obtained Tuesday shows that crew members had to use their MTA-issued cellphones to relay information about the fatal accident at Kingsbridge Road station in the Bronx.

A source said the issue was caused by a “radio failure.”

Fast-acting bystanders sprang into action after Fernando Balbuena leaped in front of the oncoming No. 4 train around 8 a.m. — with his little girl, Fernie Balbuena, in tow.

As Fernando’s lifeless body lay underneath the stopped train, two heroes jumped onto the tracks to coax the little girl out from under the car.

Miraculously, she was unscathed, save for a cut to the head and left leg, the report said.

Fernando Balbuena was pronounced dead at the scene.

The MTA didn’t immediately return a message seeking comment.