Airplanes can come in all sorts of configurations, and can perform across the broadest of performance envelopes. They can be single- engine or multi-engine, high-wing or low, fast or slow, for land or sea. Accurate descriptors the latter may all be, but aircraft are officially specified for certification purposes according to operational information relating to their speed and load limitations, and on how they’re intended to be operated.
The system of civil aircraft airworthiness designations is essentially a grouping of aircraft types and models of generally similar characteristics. The classifications “normal,” “utility,” “acrobatic,” “commuter,” and “transport” are used to describe aircraft with standard certificates of airworthiness. Aircraft with special certificates of airworthiness fall into categories such as “restricted,” “limited,” and “amateur built.” Federal licencing authorities require that these official aircraft specifications be published before an airplane’s certification can be approved. This information is found in every aircraft’s pilot’s operating handbook.
The normal, utility, and aerobatic categories are each limited to airplanes with a seating configuration (excluding pilot seats) of nine or less. Their maximum certificated takeoff weight can not exceed 5700 kg (12,566 lbs.). Normal category aircraft are intended for non- aerobatic operations, the latter being defined as any manoeuvre incidental to normal flight, stalls (other than whip stalls), steep turns in which the angle of bank does not exceed 60 degrees, chandelles, and lazy eights.
For utility category aircraft, some limited aerobatic operations are permitted. Such operations include spins (if approved for the particular type of airplane), and steep turns, or similar manoeuvres, in which the angle of bank is more than 60 degrees but not more than 90 degrees. Aerobatic category airplanes are intended for use without restrictions, other than those shown to be necessary as a result of certification flight testing.
Most small airplanes fall within the normal category, though some normal category airplanes can also be certified in the utility category. Utility aircraft can withstand stronger loads than normal category aircraft but certain allowable manoeuvres must be carried out at reduced weight and airspeed, narrower centre of gravity range, and with baggage compartments and rear seats empty. Utility category aircraft are primarily used for pilot training.
The commuter category is limited to propeller-driven, multi-engine airplanes that have a seating configuration (excluding pilot seats) of 19 or less, and a maximum certificated takeoff weight of less than 8618 kg (19,000 lbs.). Commuter category operations, as for the normal category, are limited to manoeuvres incidental to normal flying, stalls (except whip stalls), and steep turns in which the angle of bank is not more than 60 degrees.
The transport category applies to multi-engined aircraft primarily intended for the regular public transport of passengers and/or cargo for hire or reward. They typically have maximum takeoff weights greater than 5700 kg (12,566 lbs.), and they must be flown by at least two pilots. Transport category aircraft design is such that they require duplication of critical elements. Loading on wings and tailplane structures must be designed in such a way that secondary structures will allow the aircraft to continue to fly safely should any primary structure fail. The restricted category applies to aircraft used for special applications such as aerial fire-fighting and aerial photography. The limited category applies to airplanes which have been accepted for use in the military. Amateur built aircraft are designated as those built by their owners. Category designations go on to include definitions for such vehicles as rotorcraft, manned free balloons, and airships.
Design and performance codes are what distinguish the categories one from the other. While weights and manoeuvres, as described above, are what primarily distinguish categories, hundreds of elements are in fact what define the categories. These elements include: flight conditions, (performance in stall, takeoff, climb, etc,) controllability, stability, flight and control surface loads, ground loads and fatigue evaluation, design and construction, powerplant installation, equipment functionality, operating limitations, etc. Nothing is left undefined as to how an aircraft is categorized for certification.