Trombone trailer is a name for a flat trailer which extends when required to carry long loads. Trombone trailers may also be called:
- flat extender trailers
- flat extending trailers
- platform extender trailers
- platform extending trailers
Trombone trailers are built around a central steel box beam which carries a second beam within. The inner beam extends telescopically and is pinned in an extended position.
Normally a trombone trailer splits a few metres behind the headboard, providing deck surface on both sides of the split, to enable secure loading and lashing of the burden.