National Airspace System: Observations on American Airlines' 1997 Study of Future Air Traffic Congestion

Published by the Government Accountability Office on 1999-01-29.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

Resources, Community,        and
Economic Development         Division


January 29,1999

The Honorable James L. Oberstar
Ranking Minority Member
Committee on Transportation
 and Infrastructure
House of Representatives

Subject: National Airspace Svstem: Observations on American Airlines’ 1997 Studv of
         Future Air Traffic Conaestion

Dear Mr. Oberstar:

In 1995, the Federal Aviation Administration (FAA) estimated that airline delays
caused by air traffic congestion increased the industry’s operating expenses by
approximately $2.5 billion per year. That cost is higher today and is expected to grow
with increasing congestion in the air traffic system. In a 1997 study entitled w
Flight: Preserving Airline Opportunitv, American Airlines concluded that by 2005
airline flight delays would negatively affect airlines’ ability to operate their flight
schedules and by 2014 these delays could become even more severe. Others, such as the
National Civil Aviation Review Commission, have also concluded that delays are likely
to grow at an ever-increasing rate,’ producing additional negative effects on the National
Airspace System” and on the nation’s economy as a whole.

In preparation for an upcoming congressional debate on the reauthorization of FAA’s
programs, you asked us to review American Airlines’ study and provide our observations
on its findings. We also reviewed other studies of air traffic congestion, assessed the
limitations of these types of studies, and identified next steps in addressing the problem
of air traffic congestion-

* In 1996, the Congress established the National Civil Aviation Review Commission to review FAA’s
financing and evaluate FAA’s safety programs. The Commission issued its report, Avoidinp Aviation
Gridlock and Reducina the Accident Rate: A Consensus for Change, in Dec. 1997.
’The National Airspace System consists of the air traffic control system-a vast network of radars and
automated data processing, navigation, and communication equipment--and air traffic control facilities.
Other components include airports or landing areas; rules, regulations and procedures; and personnel and

                 GAO/RCED-99-66R        Observations   on Projections   of Future Air T-raffic Congestion

In summary, American Airlines’ study focused on two scenarios of future air traffic
congestion. Under the first scenario--most frequently cited by others--the study found
that by 2005 airline flight delays would interfere with airline flight schedules and by
2014 these delays would have a crippling effect on scheduled flight operations. This
scenario assumed that air traffic would grow at a rate of 2.3 percent annually and that
the current National Airspace System would not be modernized. We found, as did
American Airlines, that the “do nothing” scenario is unrealistic because it ignores
various actions under way or planned by FAA and others to alleviate future air traffic
congestion. The second scenario also assumed that air traffic would grow by 2.3 percent
annually, but in contrast to the first scenario, it factored in plans to modernize the
National Airspace System. Under this scenario, American Airlines concluded that with
the implementation of a new system of air traffic management known as free flight,
 delays through 2025 would be substantially shorter than the average delay of 1.5
 minutes experienced in 1996.

Officials from two consulting firms that also studied air traffic congestion--MITRE
Corporation and the Logistics Management Institute (LMI)-told us the American
Airlines study was important because it elevated a problem that had not received
sufficient attention. However, these officials also stated that the value of the study was
limited because it did not discuss in detail (1) air traffic congestion at lower altitudes,
where MITRE and LMI consider the problem to be most severe, and (2) the
methodologies and sources of data that were used to develop the study’s results. In
addition, we found that studies of future air traffic congestion are inherently limited by
the difficulty of predicting factors such as air traffic growth and the impact of new
technologies and procedures.


In 1997, American Airlines conducted its Free Flight: Preserving: Airline Opportunitv
study to answer key concerns about investments in free flight technologies. The airline
wanted to determine at what point in the future its scheduled flight operations would be
constrained by congestion in the National Airspace System. The study included two
principal goals: (1) to determine the impact of future air traffic congestion on airline
flight schedules and (2) to compare its results with those of other industry studies
conducted to date. In performing this study, American Airlines used a model that
simulated future air traffic congestion at higher altitudes4 under two scenarios (see enc.
I). The first scenario assumed that air traffic would grow at a rate of 2.3 percent

 3 Free fight is to provide controllers and pilots with new technologies and procedures that will allow them to
 increase the safety, capacity, and efficiency of air traEc operations throughout the National Airspace
 4 In general, higher altitudes refer to airspace above 18,000 feet, while lower altitudes refer to airspace from
 the surface up to 10,000 feet.

 2                 GAO/RCED-99-66R        Observations     on Projections   of Future Air Traffic Congestion

annually and that the current National Airspace System would not be modernized. The
second scenario assumed the same rate of growth in air traffic, but unlike the previous
scenario, it incorporated a new system of air traffic management known as free flight
into the current National Airspace System.’

Under the first scenario, American Airlines concluded that the current air traffic system
would begin to experience serious delays by 2005 and that these delays could increase
substantially by 2014. American Airlines also concluded under this scenario that each
flight within U.S. airspace would incur an average air delay of about 4 minutes in 2014--
up from an average delay of about 1.5 minutes in 1996.” Although the study did not
elaborate on the significance of such air delays, it suggested that an air delay of 4
minutes could create a ripple effect throughout the system that would result in a ground
delay of up to 2 hours at the nation’s 50 busiest airports. However, because American
Airlines maintained that the data for its study are proprietary, we were unable to
independently assess the significance of a $-minute air delay or determine how it could
result in delays of up to 2 hours on the ground.

Under the second scenario, American Airlines concluded that with the implementation
of free flight, delays through 2025 would be substantially shorter than the average delay
of 1.5 minutes experienced in 1996. In arriving at this conclusion, American Airlines
assumed that distances between aircraft could be reduced from the current 7 miles to 3
miles at higher altitudes and 4 miles to 2 miles at lower altitudes. Eventually, however,
American Airlines concluded that more runways would be needed to allow the airline to
continue to run its scheduled operations efficiently.

According to American Airlines, its study was complemented by other studies that used
similar assumptions with different methods and models. Of particular interest,
American Airlines noted, were studies by MITRE and LMI.


Like American Airlines, MITRE and LMI found that air traffic congestion is likely to be
a problem in the future if FAA, airports, and airlines do nothing to address this problem.
However, the authors of all three studies agreed that this “do nothing” assumption is
unrealistic. While American Airlines focused its analysis on air traffic congestion at
higher altitudes, MITRE and LMI focused their analyses on congestion at lower

’ To approximate conditions in the future National Airspace System under tiee flight, the study used
reduced separation distances between aircraft as a surrogate for modernization. Ultimately, new
technologies and procedures planned under fi-ee flight are expected to allow for safe reductions in these

6 According to American Airlines, 4 minutes is commonly used as the limit of average delay for on-time
scheduled airline operations in airport capacity studies.

3                GAO/RCED-99-66R        Observations    on Projections   of Future Air Trsffic   Congestion

altitudes, where they consider the problem to be most severe. According to MITRE and
LMI, congestion at lower altitudes contributes to congestion at higher altitudes. Despite
these limitations, MITRE and LMI officials stressed that the American Airlines study
was important because it highlighted a problem that had not yet received sufficient

In performing a limited analysis of domestic air traffic congestion, MITRE found that
except in a small fraction of airspace, air traffic congestion is a limited problem at
higher altitudes today. Assuming that FAA’s current modernization initiatives--such as
free flight--are implemented as planned, MITRE concluded that serious widespread
congestion at higher altitudes is not likely to materialize for at least another decade.

At lower altitudes, MITRE found that congestion is already substantial at major
airports and is expected to grow. Assuming the same annual 2.3-percent increase in air
traffic as American Airlines assumed, MITRE predicted the need for a 60-percent
increase in airport capacity by 2015 to maintain delays at today’s levels. MITRE
suggested that a combination of new runways and new operating procedures enabled by
technology (such as new tools expected to improve controllers’ ability to efficiently
sequence air traffic) could allow reductions in the required distance between aircraft and
substantially augment ai+ort capacity. MITRE is now embarking on a more detailed

LMI also found in its analyses of air traffic delays that congestion is currently minimal
at higher altitudes. According to LMI officials, congestion is found at lower altitudes,
especially around 10 to 15 major airports, such as JFK International Airport. They also
stated that congestion at lower altitudes would worsen over time. As a first step toward
addressing this problem, LMI suggested that the aviation community maximize the use
of existing concrete (such as runways and gates) with new technologies. Eventually,
LMI believes that airlines may have to make better use of underutilized airports or
readjust their flight schedules.


We found that any study of air traffic congestion is limited by many variables and these
variables are subject to change. Specifically, we found that

 l   estimating traffic growth rates with any degree of confidence is extremely difficult,
     given fluctuations in economic conditions in the United States and abroad,
 0   airlines’ plans to reconfigure operations remain unknown;
 l   the impact of new technology is uncertain;

                GAO/RCED-99-66R    Observations   on Projections   of Future Air Traffic   Congestion

l   FAA’s ability to deliver new technologies on time with the expected benefits (e.g.,
    free flight) is questionable in view of the agency’s poor modernization track record;
l   airports’ plans for expansion are unknown because funding and other variables are


To address future air traffic congestion, close coordination among FAA, airports,
and airlines will be necessary to identify bottlenecks and their causes and to
develop solutions to the congestion problem. Because air traffic congestion
problems vary in degree with factors such as the (1) location and layout of an
airport and (2) complexity of airspace, no single solution can mitigate congestion.
As a result, more detailed studies-tailored    to analyze problems at specific
airports and/or in sections of airspace-will  be important in determining the
impact of any proposed course of action (such as the use of new technologies and
procedures) on air traffic congestion.


To provide our observations on the findings of the American Airlines study, we (1)
analyzed the study, (2) compared the study’s findings with those of other air traffic
congestion studies conducted by the MITRE Corporation and by the Logistics
Management Institute, and (3) interviewed the authors of these studies. We did not
independently verify the projections of any of these air traffic congestion studies and
could not have done so for the American Airlines study, since the airline regarded its
data as proprietary information. We also assessed the limitations on performing any air
traffic congestion study and determined the next steps needed to help resolve air traffic
congestion. To gain a better understanding of the limitations of air traffic congestion
studies, we compared past air traffic growth projections with actual growth, reviewed
the types of assumptions used to conduct these analyses, and consulted with economic
experts. Through consultations with the studies’ authors and our prior work in this
area, we identified important next steps in addressing air traffic congestion. We
conducted our review from November through December 1998 in accordance with
generally accepted government auditing standards.

              GAO/RCED-99-66R    Observations   on Projections   of Future Air Traffic   Congestion


We provided copies of this report to the Department of Transportation for review and
comment, and the Department had no comments.

As you requested, unless you publicly announce its contents earlier, we plan no further
distribution of this report for 7 days. We will then send copies to the Secretary of
Transportation and the Administrator of the Federal Aviation Administration. We will
also make copies available to others upon request.

If you or your staff have any questions or need additional information, please call me at
(202) 512-2834. Major contributors to this report were Danielle Bartoni, Chuck Bausell,
Beverly Dulaney, Pete Maristch, Belva Martin, and John Noto.

Sincerely yours,

Gerald L. Dillingham        c
Associate Director,
 Transportation Issues

Enclosure - 1

 6              GAO/RCED-99-66R   Observations     on Projections   of Future Air Traffic   Congestion
    ENCLOSURE I                                                                      ENCLOSURE I

                American Airlines’ 1997 Projections of
                Flight Delays--Current Versus Future
                National Airspace System (NAS)

+ Scenario 1:
  Current NAS-
    No change except
    for an annual traffic
    growth rate of 2.3%

H Scenario 2:
  Future NAS-
    Reduced separation
    standardsa with an
    annual traffic growth
    rate of 2.3%
                                                             Avemp Air D&y      Per Flight

                            a Separation standards are distances that aircraft are required to maintain
                                 from one another.

                            Source: Free Fp,                                      American Airlines,
                                Sept. 22.1997.

(348 143)

7             GAO/RCED-QS-66R   Observations     on Projections      of Future Air Traffic Congestion
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