Complex sentence: Sara informs them that they can't get to the lead engine because the second locomotive is a streamlined F-unit with no forward catwalk, and that its nose door, which would normally allow access to the lead engine, is jammed.
Split into simpler sentences: Sara informs them that they can't because the second locomotive is a streamlined F-unit with no forward catwalk. Its nose door, which would normally allow access to the lead engine, is jammed.