Freight aircraft, commonly referred to as freighters, are airliners designed or converted for cargo hauling. They are devoid of passenger amenities, and generally feature one or more large doors for the loading and unloading of cargo.
Most conversions are carried out on older aircraft no longer suitable for passenger use, often due to changing safety or noise requirements, but there is also a market for new-build freighter designs. Note that the class is distinct from the related cargo aircraft, which are typically designed strictly for cargo.
The Boeing 747 can be ordered in a freighter version with a large nose door which could be raised above the cockpit for loading. The bulged top deck housing the cockpit was originally designed to allow an unobstructed main deck, and to keep cargo from crushing the pilots in the case of an accident. The interior size of the fuselage is matched to the size of a standard cargo container, stacked two high and two wide.
Freighters may be operated by civil passenger or cargo airlines, by private individuals or by the armed forces of individual countries. They are often adapted from aircraft originally designed for passenger use, perhaps when the aircraft type is considered to have become uncompetitive in passenger airline service. Most air freight is however carried in the cargo holds of passenger aircraft.