Page 185 - Planning and Design of Airports

152 Airp o r t Pl anning

of general aviation aircraft based at an individual airport and the num-
ber of general aviation and military operations are also prepared.
In aggregate forecasting, the entire system of airports is exam-
ined relative to the geographic, economic, industrial, and growth
characteristics of a region to determine the location and nature of
airport needs in a region. The disaggregate forecast then examines
the expected demand at local airports and identifies the necessary
development of the airside, landside, and terminal facilities to pro-
vide adequate levels of service. Within the two levels of forecasting
there are certain techniques which enable the planner to project such
parameters as annual, daily, and hourly aircraft operations, passen-
ger enplanements, cargo, and general aviation activity. In disaggre-
gate forecasting, there are many significant variables. The forecast
of each variable is quite important because it ultimately determines
the size requirements of the facilities which will be necessary to
accommodate demand. Often, the forecasts of the different variables
are linked by a series of steps, that is, originating passengers are
forecast first, this then becomes a component in the forecast of
enplaned passengers, which leads to a forecast of annual operations,
and so on.
The type of forecast and the level of effort depend on the purpose
for which the forecast is being used. Forecasts are typically prepared
for short-, medium-, and long-term periods. Short-term forecasts, up
to 5 years, are used to justify near-term development and support
operational planning and incremental improvements or expansion of
facilities. Medium-term forecasts, a 6- to 10-year time frame, and
long-term forecasts of 10 to 20 years are used to plan major capital
improvements, such as land acquisition, new runways and taxiways,
extensions of a runway, a new terminal, and ground access infrastruc-
ture. Forecasts beyond 20 years are used to assess the need for addi-
tional airports or other regional aviation facilities [1].

Forecasting Methods
There are several forecasting methods or techniques available to air-
port planners ranging from subjective judgment to sophisticated
mathematical modeling. The selection of the particular methodology
is a function of the use of the forecast, the availability of a database, the
complexity and sophistication of the techniques, the resources avail-
able, the time frame in which the forecast is required and is to be used,
and the degree of precision desirable. There are four major methods:
• Time series method
• Market share method
• Econometric modeling
• Simulation modeling