Forecasting Airport Traffic

Planning for an airport and building a credible airport investment program require that future traffic be forecast in a thorough, sensible manner. An overly optimistic forecast may cause premature investment costs and higher-than-needed operating costs; an overly conservative forecast will promote increased congestion with high levels of delay and potentially lost revenues.

Some important factors that need to consider in the planning for a specific airport include the following:

• Unusual demographic factors existing in the community

• Geographic factors that will affect the amount of airplane use

• Changes in disposable income permitting some travellers to travel more

• Nearby airports whose operation may draw from the airport being planned

• Changes in how airlines use the airport (more hubbing, route changes, etc.)

• New local industry, meaning more jobs and more business travel

• New resort and convention industries or capacity that will bring vacation travellers

Requirements Analysis:

Capacity and Delay Armed with the demand forecasts and having developed an inventory of the airport and reviewed its condition, the planning proceeds to determine the capability of the airport to accommodate the forecast demand. First is the determination of the capacity of the airport relative to the demand, with special attention to the delay that will be incurred at peak times. Capacity is used to denote the processing capability of a facility to serve its users over some period of time. For a facility to reach its maximum capacity there must be a continuous demand for service. At most facilities such a demand would result in large delays for the user and eventually become intolerable. To develop a facility where there was virtually no delay would require facilities that could not be economically justified. The second key aspect in the requirements analysis is to assess the capability of the airport to provide the traffic controls during poor weather flying conditions (IFR) as well as during good weather conditions (VFR). Except in airspace under positive control, VFR flying is based on a “pilot beware” or “see and be seen” approach to flying. General aviation pilots flying in VFR need only a functioning radio and altimeter. Commercial aircraft and many business aircraft are equipped with beacons, radar, and other equipment that permits them to fly in instrument weather and in controlled airspace. Capability for landing on a given runway and the use of navigation aids varies from airport to airport. “In discharging its responsibility for managing the air traffic control system and in assuring flight safety, the FAA performs a number of functions which have a direct bearing on the development of the master plan” *FAA, 1985+. Of particular interest are the following:

1. Establishment of air traffic control procedures for a particular volume of terminal airspace

2. Determination of what constitutes an obstruction to air navigation.

3. Provision of electronic and visual approach and landing aids related to the landing, ground control, and takeoff at the airport.

Airport Site Determination and Considerations

It is often situations within 10 miles of the airport site that will have significant bearing on the success of an airport project. The airspace and associated ground tracks along the takeoff and landing corridors are critical not only to site location, but also for runway orientation, since they define:

v Where safe landing of aircraft for over 95% of the wind conditions must occur

v Where obstacles projecting into the flight path must be eliminated

v Where houses, buildings, and recreation sites could be subjected to unacceptable levels of aircraft noise.

Siting of runways must seek to provide solutions to all three of these constraints. In addition, runways must avoid landing and takeoff paths that are over landfills and other areas that are prime bird habitats. In recognition of the severity of aircraft crashes when they occur in the vicinity of public assembly buildings, particularly schools, communities are encouraged to control the land use within 3 miles from the airport reference point (ARP), restricting the building of any such buildings [FAA, 1983a]. Other site considerations are the usual civil engineering concerns of soil condition, required grading and earthwork, wetlands, and suitable access connecting the airport with major business and industrial areas nearby.

Airside Layout and Design

Design begins with the knowledge of both the performance and physical characteristics of the aircraft that will use the airport. The approach or landing speed defines an aircraft category as A, B, C, or D. The designation of aircraft size is based on grouping aircraft according to the length of their wingspan, called aircraft design group (ADG), as follows:

Ø Group I: up to but not including 49 ft (15 meters)

Ø Group II: 49 ft (15 m) up to but not including 79 ft (24 m)

Ø Group III: 79 ft (24 m) up to but not including 118 ft (36 m)

Ø Group IV: 118 ft (36 m) up to but not including 171 ft (52 m)

Ø Group V: 171 ft (52 m) up to but not including 214 ft (65 m)

Ø Group VI: 214 ft (65 m) up to but not including 262 ft (80 m)

The important physical characteristics of the aircraft affecting airport design are maximum takeoff weight (W), wingspan (A), length (B), tail height (C), wheel base (D), nose to centerline of main gear (E), undercarriage width (1.15 ¥ main gear track, F), and line-of-sight/obstacle-free zone at the nose of the aircraft. Figure 5.3 displays a major problem faced by aircraft as they land and travel on the runway, taxiway, or taxi-lane system. The pilot’s view of the ground directly in front of the aircraft is obscured by the nose. This blind zone for the pilot is known as the object-free zone (OFZ) and is important for safe ground movement of aircraft. It affects the geometric design of the runway and taxiway