Why do some missions limit the amount of passengers and depart with empty seats?
Good question and the answer (a factor of crew availability and loaded cargo) lies in the USAF Instructions Series 11 (Flying Operations). As an example, a C-5 can accommodate 73 folks in the passenger compartment but some flights may depart with only 19 passengers. Other factors could include type (security) of cargo or availability of adequate safety equipment but the main reasons for seat limitations are listed below for the more common aircraft: • C-5: Cargo (not crew) limitation. 20 passengers and above requires an open pallet position for passenger baggage. Therefore, if there is a full cargo load then the 73-passenger compartment is limited to 19 passengers. • C-17: Crew limitation. Above 40 passengers requires an additional crew member. • KC-10: Crew limitation. Above 40 passengers requires an additional crew member. • KC-135: Crew limitation. Above 10 passengers requires an additional crew member.
