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 acceptable under certain airworthiness requirements.
In the United States, Federal Aviation Regulations Parts 25 and 29 are applied to the design and certification of transport category airplanes and helicopters respectively.
In Europe the European Aviation Safety Agency has similar certification requirements, also titled Parts 25 and 29, for application to transport category airplanes and helicopters.
Design requirements for the transport category rotorcraft do not specify upper or lower limits on the maximum takeoff weight or number of passenger seats but examples of these helicopters typically have maximum takeoff weights greater than 7,000 lb (3 175 kg).
Easily recognisable examples of transport category helicopters are Bell 412, Eurocopter AS332 Super Puma, MBB/Kawasaki BK 117, AgustaWestland AW139.