Transport aircraft are designed primarily for the carriage of personnel and/or cargo. Since they contain a good deal of interior space, it is quite common to see variants, such as C3I-ISR, tanker, etc. Even within the transport mission, the aircraft can often be reconfigured for carrying cargo, passengers, or patients in litters.
Commercial airliners, of course, are passenger transport aircraft optimized for carrying passengers, with varying levels of luxury. There are also cargo carriers in widespread commercial use.
In a few cases, other aircraft types, usually bombers have been converted to transport roles. This is most common when the mission calls for higher speed than is typical for transport aircraft; the distinction tends to disappear with large jet aircraft.
Categorizing by range
Transport aircraft may be classed according to range:
- Short-range — No more than 1200 nautical miles at normal cruising conditions (2222 km). This includes virtually all helicopters and tilt-rotor aircraft
- Medium-range Between 1200 and 3500 nautical miles at normal cruising conditions (2222 and 6482 kn)
- Long-range — Exceeds 3500 nautical miles at normal cruising conditions (6482 km).
Some transport aircraft can be refueled in midair, giving effectively unlimited range. Most large refueling tankers are based on transport aircraft; a subset of tankers can both give and receive fuel. For extremely long-range operations, as in the Falklands War, a group of tankers may start off a mission, with some tankers being refueled by other tankers, which then turn back. The process may be repeated; it could take more than 10 tankers to get two bombers over the Falklands.
Categorizing by mission
Some transports are tactical, and able to land on short, unimproved runways. In the case of helicopters and tilt-rotor aircraft, they may need no runway at all. These tend to be medium to small in size; while some large transports have been built with short-field capability, they tend to be too valuable to risk in tactical operations.
For strategic missions, "large" may be interpreted in different ways. One, of course, is straightforward: the amount of weight the aircraft can lift. In other cases, the limitation is volume or interior height rather than weight. Some bizarre-looking variants, with such names as Very Pregnant Guppy, have been made to carry oversized but not extremely heavy cargoes, such as space launch vehicles.