Runway Pavement Classification
The undercarriage design depends on how the wheels interact with the airfield surface. An airport runway surface must be designed to withstand an aircraft’s weight not only at the static condition but also at dynamic loading (e. g., for a heavy landing). Runway pavement loading is known as flotation. Among airports, the runway pavement strength varies. There are three main types of surfaces, as follows:
Table 7.2. Load classification group
2. Type 2: Prepared Macadam Surface. These are asphalt – or tar-topped runways with strength built in by the thick macadam filler; these are designated as a Type 2 surface. These surfaces are less expensive to prepare by using a heavily rolled macadam filler. However, local depressions can cause the surface to undulate, and it requires frequent maintenance with longer downtime. This type of runway can accommodate heavy aircraft such as the B747.
3. Type 3: Prepared Concrete Surface. This is a rigid concrete runway designated as a Type 3 surface. These runways are built with pavement-quality concrete (i. e., about a half-meter thick) and are covered by asphalt (e. g., 150 mm thick). All major international airports have Type 3 runways, which can take a load similar to a Type 2 surface and do not have to be as thick. This type is expensive to prepare and maintenance downtime is minimal. Cracks are the typical type of failure that occurs. A Type 3 surface can accommodate heavy aircraft such as the B747 and the A380.
Aircraft designers must design aircraft to be compatible with existing airfields in order to operate. If the market demand necessitates larger and heavier aircraft, then designers must make the aircraft comply with the pavement strength of existing airfields or the airfield must be reinforced to accept the heavy aircraft. Runway reinforcement depends on new designs; therefore, airport authorities communicate with aircraft manufacturers to remain current with market demand. When the B747 began operating, almost all international airfields needed reinforcement to accept them – some were not operational for several years.