If a vehicle has an air compressor assisting the hydraulic brakes, what endorsement is needed?

For a vehicle equipped with an air compressor that assists the hydraulic brakes, no specific endorsement is needed because the air compressor is not the primary braking system and doesn't qualify the vehicle as an air brake-equipped vehicle. This means that standard hydraulic brake training is sufficient for operation, thus not requiring an additional endorsement.

Endorsements such as the Q or S are typically related to more specialized vehicles, such as those utilizing air brake systems or requiring special skills for operating a bus or school bus. The C Endorsement is also related to specific vehicle classifications that would necessitate extra training requirements. Since the vehicle in question primarily relies on hydraulic braking, none of these additional endorsements are applicable, reaffirming that the answer of no endorsement needed is indeed accurate.