AIRLINE ROUTE AND SCHEDULE

PLANNING
UNIT 2
CAPACITY AND DELAY
 Introduction
The efficient movement of aircraft and passengers between airports is highly
dependent on two key characteristics of an airport’s operations: the demand for
service by aircraft operators and passengers and the capacity at the airport, both in
airspace and local environment. A major concern of airport planning and
management is the adequacy of an airport’s airfield, specifically in relation to the
layout of the airport’s runways, to handle the anticipated demand of aircraft
operations. If air traffic demand exceeds airport or airspace capacity, delays will
occur, causing expense to air carriers, inconvenience to passengers, and increased
workload for the FAA air traffic control system as well as airport employees and
administrators. With aviation growth, associated flight delays will increase as well,
unless the capacity of the nation’s airports and airspace system increases to
accommodate the demand.
There are a number of potential specific reasons for any given aircraft to experience
delay. The most common factors that might cause an aircraft to experience delay
are weather, aircraft mechanical issues, or simply operating at a time when overall
demand for operations exceeds capacity. The FAA estimates that the majority of
flight delays occur because of adverse weather. Other delays are attributed to
equipment, runway closures, and excessive volume or demand
 Defining capacity
Capacity, in general, is defined as the practical maximum number of operations
that a system can serve within a given period of time. Capacity is, in fact, a
rate, similar to velocity. An automobile for example, might travel at a rate of
50 miles per hour, meaning that over an hour, travelling at this rate, the
automobile will travel 50 miles. Travelling this rate for 30 minutes, the
automobile will travel 25 miles, and so forth. Airport capacity is measured in
aircraft operations per hour. A single runway at an airport, might have an
operating capacity of 60 operations per hour, meaning, over the course of
an hour, the airport will be able to serve approximately 60 aircraft takeoffs
and landings; in 30 minutes, the airport can serve 30 such operations, and
so forth.
It should be noted that although airport capacity typically refers to the capacity
to handle aircraft operations, there are other areas of operation at an
airport where other measures of capacity are equally important. For
example, the efficient movement of passengers through points within an
airport terminal is determined, in part, by the passenger processing
capacity of locations within the terminal, and the number of automobiles
that can unload passengers at an airport’s curb may be measured in terms
of vehicle capacity.
There are actually two commonly used definitions to describe
airport capacity: Throughput capacity and Practical capacity.
Throughput capacity is defined as the ultimate rate at which
aircraft operations may be handled without regard to any
small delays that might occur as a result of imperfections in
operations or small random events that might occur.
Throughput capacity, for example, does not take into account
the small probability that an aircraft will take longer than
necessary to take off, or a runway must close for a very short
period of time because of the presence of small debris.
Throughput capacity is truly the theoretical definition of
capacity and is the basis for airport capacity planning.
Practical capacity is understood as the number of operations
that may be accommodated over time with no more than a
nominal amount of delay, usually expressed in terms of
maximum acceptable average delay. Such minimal delays may
be a result of two aircraft scheduled to operate at the same
time, despite the fact that only one runway is available for
use, or because an aircraft must wait a short time to allow
ground vehicles to cross
 Factors affecting capacity and delay
The capacity of an airfield is not constant. Capacity varies considerably based
on a number of considerations,
including the utilization of runways, the type of aircraft operating(known as
the fleet mix), the percentage of takeoff and landing operations being
performed, ambient climatic conditions, and FAA regulations which
prescribe the use of runways based on these considerations.
Much of the strategy for successful management of an airfield involves
devising ways to compensate for a number of factors that, individually or in
combination, act to reduce capacity or induce delays. The physical
characteristics and layout of runways, taxiways, and aprons, for example,
are basic determinants of the ability to accommodate various types of
aircraft and the rate at which they can be handled. Also important is the
type of equipment, particularly the presence of instrument landing systems,
installed on the airfield as a whole or on a particular segment.
One of the characteristics that affects an airport’s capacity is the configuration
of its runway system. Although every airport is different, the configurations
of airport runways may be placed in the following categories: single runway,
parallel runways, open-V runways, and intersecting runways. Although
every runway configuration has a uniquely different capacity that is
determined by a variety of factors.
Figure 12-6. LAHSO (land and hold short
operations) on intersecting runways
 CONTD…
Another significant factor in determining airport capacity is the consideration
of the volume of demand and characteristics of the aircraft that wish to
use the airport during any given period of time. For any given level of
demand, the varying types of aircraft with respect to speed, size, flight
characteristics, and even pilot proficiency will in part determine the rate at
which they can perform operations. In addition, the distribution of arrivals
and departures to the extent to which they are bunched rather than
uniformly spaced, as well as the sequence of such operations, also play a
part in determining an airport’s operating capacity. In part, the tendency
of traffic to peak in volume at certain times is a function of the flight
schedules of commercial air carriers using an airport. For example, at
airports that serve as hubs for major air carriers, high volumes of aircraft
all arrive in banks and all depart a short time later, after passengers have
transferred from one flight to another to complete their travel. Arrival
banks of aircraft result in one level of airport capacity, whereas departure
banks result in another level of capacity, merely by the different operating
characteristics of aircraft arrivals and departures.
 Defining delay
Delay is defined as the duration between the desired time that
an operation occurs and the actual time the operation occurs.
When aircraft depart and arrive “on time,” according to their
respective schedules, for example, the aircraft is said to have
experienced no delay. If, however, an aircraft actually departs
an hour after its scheduled departure time, that aircraft is
said to have suffered 1 hour of delay. This delay may have
been the result of any number of factors. A mechanical repair
may have been required, luggage may have been slow in
being loaded, weather may have required the aircraft wait
until conditions improve, or perhaps the aircraft was one in a
large number of aircraft that were scheduled to depart during
a high-demand period time of day when the capacity of the
airfield was insufficient to accommodate such high demand.
The FAA defines the maximum acceptable level of delay as the level of
demand, in relation to throughput capacity, that will result in aircraft delays
of no more than 4 minutes per operation. Congestive delay occurs when
demand is sufficiently close to throughput capacity to result in an average
of nine or more minutes of delay per aircraft operation. As demand
asymptotically reaches throughput capacity, delays can reach several hours
per operation. During extreme periods, when both demand is at its highest
and capacity is significantly reduced because of weather or any other
adverse condition, scheduled aircraft operations may be delayed for several
days, if not cancelled. How much delay is acceptable is, in fact, based on
judgment involving three concepts. First is the concept that some delays are
unavoidable because of factors beyond human control, such as changing
meteorological conditions. Second, some delays, though avoidable, might
be too expensive to eliminate. For example, the cost of building a new
runway only to reduce delays by perhaps a few seconds per operation may
be excessive. Third, even with the most vigorous effort, because aircraft
operations are demanded on a somewhat random time frame (for example,
even though an air carrier may be scheduled to land at 12:00 noon, it might
actually wish to depart at some random period between 11:58 and 12:03,
depending on winds or other factors that determine an aircraft’s travel time
to its destination), there always exists the probability that some aircraft will
encounter delay greater than some “acceptable” amount. Thus, acceptable
delay is essentially a policy decision about the tolerability of delay being
longer than some specified amount, taking into account the technical
feasibility and economic practicality of available remedies
 Estimating delay
As with estimating capacity, various methods exist to estimate delay from
fundamental analytical models, FAA tables and graphs, and computer
simulation models. Similar to capacity estimation, analytical models allow
an airport planner to estimate delays using fundamental estimations for
aircraft demand and airport capacity. FAA tables provide cursory
estimations of delay for more complex operating conditions, whereas
computer simulation models provide detailed estimations of delay under a
full variety of operating conditions, from the very simple to the highly
complex. A common analytical tool used to estimate delay over a period of
time for a given airport capacity is the cumulative arrival diagram, also
known as a queuing diagram. The diagram is based on the highly developed
science of queuing theory, formed originally to estimate queues and delays
for automobile traffic. Queuing theory may be applied to any environment
where queues, and hence delays, occur, from toll booths, to grocery stores,
to airports. One example of a situation where a cumulative arrival diagram
is particularly useful is a period of time where the demand changes while
airport capacity remains essentially the same. This situation occurs often
within airports.
 CONTD..
Periods of high demand, known as peak periods, tend to occur during
morning and evening commute hours, at airports acting as hubs for
major air carriers, and in periods of arrival or departure. Although
the time and duration of peak periods of each individual airport is
unique, peak periods, in general, are common to virtually all
airports. Periods of time that experience less demand are known as
off-peak periods.
Similar to capacity, demand is a rate, measured in operations per hour.
Whereas capacity is the maximum number of operations that can
be handled within an hour, demand is the number of operations
that wish to occur over an hour. By definition, then, if a demand is
less than capacity, the airport is said to be operating under capacity,
and suffers minimal delays; as demand reaches capacity minor
delays increase. When demand reaches, or exceeds capacity, the
airport is said to be saturated, operating at capacity, but suffering
large delays.