Counting Ops at GA Airports
Current methods used by FAA, states need to be refined
By Dr. Maria Muia, Manager of Aeronautics Section, Indiana DOT
In an industry with exploding growth and limited funding, it’s appropriate that measures be taken to accurately record growth and to ensure funds are allocated properly to accommodate this growth. That’s the opinion of Maria Muia, aviation manager for Indiana, who recently researched methods used to count aircraft operations. Here are some of her findings.
The
U.S. accounts for 50 percent of all general aviation traffic in the world,
and GA aircraft make up over 90 percent of all aircraft in this country.
Almost 84 percent of the 5,357 airports open to the public in the U.S.
are general aviation airports, and the vast majority of these airports
do not have air traffic control towers. General aviation airports provide
service to more than 5,300 communities while the airlines serve just a
handful; yet, we don’t have a uniform way of counting the traffic
that uses our general aviation airports.
Air traffic controllers count the aircraft
that use the commercial airports, but who is counting the aircraft at
the general aviation airports? In some cases the state aviation agency
is, but in most cases the number of operations recorded at a general aviation
airport is simply a guess. Albeit an educated guess in certain cases,
but usually just a guess all the same.
We care about this information because it’s
being used for a whole host of purposes: helping to justify airport development
projects, air traffic control towers, and navigational aids. It’s
being used in airport environmental documentation, forecasting, economic
impact statements, airport planning, and the FAA Airport Master Records.
If inaccurate methods are being used to estimate operations, then anything
the resulting information is used for is questionable.
Surveying the States
I recently surveyed each state aviation
agency in the country to determine exactly what method, if any, was being
used to count and estimate aircraft operations at non-towered airports
in their states. I further analyzed these methods for accuracy, efficiency,
and cost-effectiveness.
The most popular method to estimate aircraft
operations at non-towered airports is to simply ask someone at the airport
what they think the operations are. Thirty states just ask the manager,
the FBO, or other commercial operator. The accuracy of this method is
highly questionable.
Ten states report that they multiply the
airport’s based aircraft by a predetermined number of operations
per based aircraft. For example, if an airport has 30 based aircraft and
each aircraft is believed to perform 500 operations per year, then the
airport records having 15,000 operations. The accuracy of this method
is also questionable.
Three states base annual operations on information
contained in guest logs at the airport. Many airports keep registers for
pilots to sign when they come into the terminal. These are tallied to
determine an annual estimate. But how many people actually sign these
logs? (If I am typical of most pilots, I only sign them about 50% of the
time.)
Eighteen states take a sample of actual
operations and estimate annual operations from the sample. This method
has some degree of statistical accuracy, but there are still concerns
about how and when the samples are taken. Furthermore, there is concern
about how the sample is expanded into an annual estimate.
Two states use information received in planning
studies as their source for operations estimates. These studies include
individual airport master plans, regional plans, and state system plans.
One state contacts commercial carriers located at the airport and asks
what the annual operations are. These are tallied into an annual count
for commercial operations — but what about the non-commercial?
It’s interesting to note that of the
states that responded to the questionnaire, 15 indicate that they use
more than one method, making the results incomparable with other airports
within the same state because of the different methods used.
Testing for Accuracy
Also, I researched the accuracy, efficiency,
and cost-effectiveness of each of the methods indicated. Elev-en states
report that the accuracy of their method is unknown. Thirty states indicate
that they had not performed any type of accuracy test and estimate the
accuracy of their method to be anywhere from zero to 80 percent. The most
common method used by states that don’t perform accuracy tests is
simply asking the airport manager, FBO, or others what they think the
operations are.
Fourteen states performed some type of accuracy
tests on the method used. Taking samples of actual operations is the most
common method used by states that had actually performed accuracy tests
(11 of the 14 took samples). States that perform accuracy tests generally
believe their methods to be more accurate.
The least time-consuming and least expensive
method to estimate operations is by simply asking the airport manager,
FBO, or other personnel what they think the operations are — the
cost being just the time it takes to ask the question. Normally, the state
airport inspector is already at the airport doing an inspection and asks
the question. This is the least accurate method. Since 37 states actually
use operations information to justify airport development projects, there
is considerable incentive for an airport to exaggerate its operations.
The most accurate method to count and estimate
aircraft operations, on the other hand, is to actually sample operations
and then expand the sample into an annual estimate. The sample, however,
must be long enough and done throughout all four seasons to be accurate.
Generally eight weeks is believed to be the most accurate with two weeks
sampled in each of the four seasons. Although this is the most accurate,
it is also the most expensive and time-consuming.
Methods Used
States that take samples use three different
methods: visual counts, pneumatic counters, and acoustical counters (RENS
counters and Larson Davis counters). Taking visual sample counts is the
most accurate, expensive, and time-consuming of the sampling techniques,
and most states find it too cost-prohibitive to do for eight weeks over
the entire year.
Pneumatic-type counters are connected to
a tube placed across taxiways and ramps. When an aircraft passes over
the tube, a pulse of air is created and travels through the hose, triggering
the counter. Pneumatic counters can be very inaccurate depending on the
layout of the airport and the amount of non-aircraft vehicular traffic
using the taxiways. Also, these counters fail to record touch-and-go operations.
The most accurate and least expensive approach
is to use acoustical counters, which actually record the noise the aircraft
makes and tallies the operations. However, there is not consensus on the
accuracy of the acoustical counters currently in use. While the Larson
Davis counter is less labor intensive than the RENS counter, the accuracy
is still under question. Eight states that use Larson Davis report varying
degrees of accuracy — from 60 to 99 percent. (The Indiana DOT conducted
extensive tests of the RENS counter and found them to be approximately
90 percent accurate.)
FAA Requirements
States estimate aircraft operations at non-towered
airports for a variety of reasons, the most common being for the FAA Airport
Master Records. FAA has a statutory obligation to "collect, maintain,
and disseminate accurate, complete, and timely airport data for the safe
and efficient movement of people and goods through air transportation."
An Airport Master Record (Form 5010) for
each airport is updated for the Airport Safety Data Program. Forty-two
states use airport operations data to fill in item numbers 100-105 on
this form. Information on the Airport Master Record is made available
to the general public. At least three states have intricate traffic counting
programs, but still use the airport manager’s estimate on the Airport
Master Record.
FAA Airport Safety Data Program Order 5010.4
directs the airport inspector to record the total number of operations
on FAA Form 5010. It further stipulates that the inspector is to use "FAA
tower counts where available. If not available from FAA sources, use estimates
based on discussion with airport management and/or the FBO."
Recommendations
It makes little sense for FAA to fund certain
state’s aircraft traffic counting programs with federal grant money,
which they do in many cases, and not use the information on the official
Airport Master Record. It’s recommended here that FAA revise Order
5010.4 to include the state’s aircraft traffic counting programs
as the second source for operations information when tower counts aren’t
available. If a state doesn’t have a traffic counting program and
there’s no tower, it’s recommended that this data element on
the Airport Master Record be recorded as "unknown".
While states use annual aircraft operations
data at non-towered airports for a variety of purposes, it’s not
recommended that they use it at all if it’s simply a guess. If the
information is going to be used for project or tower justification, environmental
documentation, forecasts, economic impact statements, or the FAA Airport
Master Record, then statistical sampling should be used to determine the
airport’s annual operations.
Federal and state governments should not
base capital funding decisions, safety decisions, or environmental requirements
on information received from aircraft traffic counting programs that simply
ask the airport manager or other airport personnel what the annual operations
are. FAA shouldn’t provide funding for aircraft counting programs
and then not require the resulting information be used in the official
Master Record.
By 2010, hours flown by GA aircraft are
expected to increase to 34.1 million from the 1998 level of 28.2 million,
while general aviation aircraft are expected to increase to 220,804 from
the 1998 level of 194,800. Yet, Congress continues to fight over levels
of funding actually needed to maintain this country’s infrastructure.
In order to invest appropriately in our aviation system we must understand
the system as it exists today.