Transport category is a category of airworthiness applicable to large civil airplanes and large civil helicopters. Any aircraft's airworthiness category is shown on its airworthiness certificate. The name "transport category" is used in the USA, Canada, Europe and many other countries.
Transport category airplanes are either:
- Jets with 10 or more seats or a maximum takeoff weights (MTOW) greater than 12,500 lb (5670 kg); or
- Propeller-driven airplanes with greater than 19 seats or a MTOW greater than 19,000 lb (8618 kg).
Transport category helicopters typically have maximum takeoff weights greater than 7,000 lb (3 175 kg) although there is no lower weight limit.
The Convention on International Civil Aviation, and particularly its Annex 8 Airworthiness of Aircraft, specify standards that must be met by each civil airplane and civil helicopter that is used in international aviation. These standards apply if the airplane has a maximum takeoff weight greater than 5 700 kg, or the helicopter has a maximum takeoff weight greater than 3 175 kg.
In the US the standards in Annex 8 are incorporated in:
- for airplanes: Part 25 of the Federal Aviation Regulations titled Airworthiness Standards: Transport Category Airplanes
- for helicopters: Part 29 of the Federal Aviation Regulations titled Airworthiness Standards: Transport Category Rotorcraft
Parts 25 and 29 are applied to transport category airplanes and helicopters in the US and many other countries where large airplanes and helicopters are designed and manufactured. In Europe the European Aviation Safety Agency has similar certification standards, also titled Parts 25 and 29, for application to large airplanes and helicopters.
A principle behind transport category design standards is that any element in an airplane or helicopter can fail, but the risk of such a failure causing an accident should be extremely low. Consequently transport category airplanes and helicopters have duplicated elements wherever failure of one element is likely to cause an accident. For example, transport category airplanes must have at least two engines and be flown by at least two pilots. The loads on the wings and tailplanes are usually carried by multiple load paths. If one element of the primary structure fails due to metal fatigue or corrosion the remaining sound elements of the structure must carry the loads until the failed structural element is discovered in routine maintenance. This fail-safe principle is not necessary in airplanes and helicopters that are not certificated in the transport category.
If an element in a transport category airplane or helicopter is not highly critical, or if its failure is relatively benign, it is possible for that element not to be duplicated. For example, most transport category airplanes do not have duplicated nosewheel assemblies; and some do not have duplicated wheels on each main undercarriage.
A transport category helicopter is permitted to have only one main rotor head, and may have only one engine. If a transport category helicopter has only one engine it is only eligible to be a Class B (or Performance Group 2) helicopter. An example of a transport category helicopter with only one engine is the Bell 204/205.
Other categories of airworthiness used in the US, Canada, Australia and numerous other countries are:
- normal category
- utility category
- acrobatic category
- commuter category
- restricted category
- primary category
- manned free balloon