Caught (up) in traffic

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Daily Archives: November 24, 2012

On runway configuration and orientation

We teach our students the basics of Airport Engineering including design principles for airside and landside facilities. The most important airside facility is the runway and there are several factors affecting the determination of runway configuration and orientation. Even for single runways, these factors are critical in order to ensure safe and efficient operations. Factors affecting runway configuration and orientation include:

1) Wind – the direction and magnitude of the wind is critical for aircraft as headwinds help generate the lift required for taking-off and cushioning landings. Headwinds will tend to shorten runway length requirements due to this assistance with lift while tailwinds will tend to increase runway length requirements. Cross winds are undesirable as they may cause aircraft to roll or stall. A useful tool for establishing wind behavior (e.g., directions and speeds) is a wind rose, which requires many years of data on wind speeds along different directions to establish the best orientation for a runway. The wind rose pretty much looks like a spider graph overlaid unto a compass, illustrating along which directions the winds are strongest. Wind roses may also be constructed according to the times of the year to account for seasonality in the information.

2) Neighboring airports and airways – one can just imagine the nightmarish situations faced daily by air traffic controllers in New York where there are several major airports not just in that city but in nearby metropolitan areas as well such as New Jersey, Philadelphia and Washington, D.C. where hundreds of flights converge in what is very limited airspace. Thus, air traffic controllers would have to be mindful of the shared air space among planes operating out of the different airports in providing guidance to pilots taking off or maneuvering for a landing.

3) Obstructions – these refer to possible obstructions around the airport and particularly along the flight paths of aircraft and imaginary surfaces are drawn with respect to the proposed runway configuration to determine the height restrictions for structures and other features around the airport. These imaginary surfaces include the projection of aircraft approaches from either end of a runway (or runways) that logically should be free from any obstructions. Cities are required to strictly enforce land use regulations around an airport to ensure safety.

4) Topography – the presence of mountains or bodies of water will influence how an airport will be laid out including considerations for future development or expansion. In many cases, mountains will influence other factors such as wind and obstructions. In certain areas, airports are built over plateaus, thereby restricting development options from the start. Examples of these in the Philippines are Baguio’s and Cagayan De Oro’s airports that are also affected by fog, adding to the challenges (and hazards) faced by pilots.

5) Restricted areas – there are certain “no fly” zones in cities such as the airspace directly above sensitive areas or buildings like military camps or the official residences of heads of state/government (e.g., Malacanang, the White House, etc.) are enforced as a matter of security.

6) Bird hazards – there have been an increasing incidence of bird strikes reported in the local news with many attributed to the increase in numbers of migratory birds. These pose hazards to aircraft (even the large jetliners) as the birds can get sucked by their engines resulting to damage to the propellers or fan jets. As such, many airports employ staff to ward off birds or use devices to disperse them. These efforts, however, are limited to the airport grounds. Beyond the airport, birds, particularly those in protected areas may still pose dangers to aircraft should the areas be along the aircraft flight paths.

7) Control tower visibility – air traffic control provides guidance for aircraft operations whether they be on the ground or in the air. While there are modern, hi-tech instruments available in most large or major airports, safety and guidance is greatly enhanced with the tower visibility to pilots (and vice versa).

8) Jet blast and wing tip vortices – aircraft take-offs and landings are regulated not just in terms of who has priority over the other (e.g., landing aircraft typically have the “right of way” over those waiting to take off) but also to give some headway in order to allow for the dissipation of turbulence generated by aircraft operations. This may be especially important in cases where there are multiple runways including intersecting configurations where aircraft may cross flight paths.

9) Runway length – the required length of runway may be dependent on the types or models of aircraft that intend to use it. Larger aircraft will require longer runways with the Boeing 747s requiring about 2 kilometers for take-offs under various conditions. Smaller aircraft, of course, will require shorter runways and typical airstrips for 2-seater or 4-seater aircraft can be less than a kilometer long.

10) Environmental factors – aircraft operations inevitably lead to pollution including the emissions and noise they generate. As such, land uses around airports should be planned accordingly in order to reduce issues pertaining to noise and air quality. Unfortunately, land use regulation in Philippine cities are not strictly enforced and so there will always be developments that are incompatible with airports with ironies when communities developed after the airport complain of noise and air pollution.