The Marine Corps MOS 6176 is for a Tiltrotor Crew Chief. Crew chiefs are responsible for the maintenance and safety of the aircraft and its passengers. They also load the aircraft with cargo and fire the weapons systems.
Crew chiefs have similar responsibilities to other crew chiefs, but they focus on tiltrotor aircraft. They control everything that happens outside of the cockpit, including:
Aircraft maintenance
Cargo storage
Passenger safety
Loading the aircraft with cargo
Firing the weapons systems