Until the introduction of heavy monoplane aircraft in the latter part of the 1930s, civil air-transport aircraft were able to operate from grass runways with takeoff distances of less than 600 metres (2,000 feet). The advent of heavy aircraft such as the DC-3 required the provision of paved runways, at the same time, takeoff distances increased to more than 900 metres (3,000 feet). The length requirements for runways continued to increase into the mid-1970s, when large civilian aircraft such as the Douglas DC-8 and some models of the Boeing 747 required almost 3,600 metres (12,000 feet) of runway at sea level. (Even longer runways were necessary at higher elevations or where high ambient air temperatures occurred during operations.) The trend toward increasing runway lengths caused many problems at existing civilian airports, where runways had to be extended in order to accommodate the new aircraft. Ultimately, pressure by airport operators and the development of turbofan jet engines arrested and finally reversed the trend. Since the 1970s, runway length requirements have actually decreased, and the takeoff and climb performance of civilian aircraft has improved substantially. This has brought a dual benefit in reducing the area of land required by an airport and also in reducing the area around the airport that is adversely affected by noise on takeoff.
Runway Identification Number & Suffix Letter
General runway identification is based on the compass heading the aircraft is facing, as it is landing or taking off. For example, Runway 17/35 is facing approximately 170° in one direction and 350° in the opposite direction. Even though a runway is a single strip of concrete, it is essentially treated as two separate runways by pilots and controllers. Parallel runways have the same compass readings, and therefore are further designated with L (Left) or R (Right) at the end of the runway number.
Factors Affecting Construction And Use Of Runways
Runways are built to align with historical wind patterns specific to each airport because aircraft land and take off into the wind.
Runway Use Determination: Selecting which runways to use for aircraft departures and arrivals is a complex task. Decisions about airport configuration and runway use are made carefully on a continuous basis by the Air Traffic Control (ATC). When selecting an airport configuration, ATC takes into consideration numerous factors including:
- Wind direction and wind speed (on the surface and aloft)
- Aircraft weight
- The number of inbound and scheduled outbound aircraft
- Noise abatement
- Where aircraft are going to and coming from (destination and origin airports)
Weather is an integral factor in airport operations, aircraft performance and the flight planning process. Factors such as surface winds and winds aloft, cloud type, cloud ceiling levels, precipitation, sea level pressure and temperature are all considered by pilots and air traffic controllers before an airplane begins its journey. Aircraft land into the wind to slow to a speed capable of a controlled touch-down on the runway. Therefore, the wind direction and speed at an airport is the foundation for a host of operational decisions. While aircraft may operate with limited tail winds (less than seven knots), it is not ideal because higher ground speeds may lead to unsafe conditions upon landing. As the wind changes, the runways in use and flight paths change accordingly. Air temperature has an impact on the performance capabilities of jet engines. Colder temperatures lead to better aircraft performance and allow aircraft to climb faster when departing. Additionally, aircraft flight paths may change to be directed around severe weather, such as thunderstorms, tornados, snow storms, icing, turbulence or lighting.
At all but the smallest airports, pavements are now provided for runways, taxiways, aprons, and any other areas where aircraft are maneuvered. Pavements must be designed in such a way that they can bear the loads imposed by aircraft without failure. A pavement must be smooth and stable under conditions of loading during its expected or economic life. It should be free from dust and other particles that could be blown up and ingested into engines, and it must be capable of spreading and transmitting an aircraft’s weight to the existing subsoil (or subgrade) in a manner that precludes subsoil failure. Another function of the pavement is to prevent weakening of the subsoil by moisture intrusion, especially from rainfall and frost.
Airfield pavements are of two types, rigid and flexible. Rigid pavements are constructed of portland cement concrete slabs resting on a prepared subbase of granular material or directly on a granular subgrade. Load is transmitted through the slabs to the underlying subgrade by flexure of the slabs. Flexible pavements are constructed of several thicknesses of asphalt or bituminous concrete layers overlying a base of granular material on a prepared subgrade. They spread the concentrated aircraft wheel loads throughout their depth until the load at the base of the pavement is less than the strength of the in situ soil. At all depths the strength of the pavement should be at least equal to the loads placed upon it by aircraft wheels. Asphaltic concrete is an unsuitable material for pavement construction because of its vulnerability to damage by aviation fuel. Therefore, even at airports where flexible airfield pavements are generally in use, it is usual for concrete pavements to be used where aircraft stand on the aprons and at runway ends where fuel spillage is frequent.