Can you help me please...

The pilots had been riding through the Valley, although from the transcript of their in-flight conversations, it seemed they were somewhat uncertain and unconcerned as to excatly where they were.
“I don’t see anything over about thirteen three is the highest peak in the whole route I think,” said Rowe, the flight’s engineer.
thirteen threee... means what....
Can you explain thet part of the sentences to me.. If it's possible
Thanks