WHAT'S UNDERGROUND
FAA, Atlanta International share lessons learned
with latest runway project
A new 9,000-foot runway at the Hartsfield-Jackson
Atlanta International Airport in Atlanta was officially commissioned in May.
This runway, said to be one of the most complex structures of its kind in the
world, spans a major interstate highway and includes an 18.5 million cubic yard
embankment. Here, FAA and airport officials share some insights learned along
the way when it comes to putting in underground systems that can be easily
traced.
Hartsfield-Jackson Atlanta is the world’s busiest passenger
airport, serving more than 89 million passengers in 2005 alone. Delays at
Hartsfield-Jackson can create a ripple effect across the continent and hamper
airport efficiency all across the nation. Consequently, the new runway has been
called the most important runway in North America.
The Southeast Region office of the Federal Aviation
Administration (FAA) is responsible for installing and maintaining
flight-related airport facilities for this expansion, including navigational
aids, instrument landing and approach lighting systems, and the buried cables
required for these functions. As new cables were buried adjacent to the new
runway, approximately 1,000 discrete locations were electronically marked as a
safety measure and to facilitate future maintenance.
According to FAA Project Engineer Brian Murphy, the
traditional means of identifying the location of buried airport facilities has
been to place 2’x2’x6” concrete markers flush with the ground, immediately
above marked features. These heavy markers cost about $100 each, and require
painting as well as ongoing attention to remove grass clippings and repair soil
erosion. They can be easily displaced by mowing equipment, which can compromise
facility records and excavation accuracy.
The traditional means of tracing buried airport facilities
involves the use of locating equipment which senses an electromagnetic field
created when an applied signal current flows through the buried conductive
elements to a distant ground point. Murphy notes that this process is effective
for tracing isolated metallic cables, but delivers ambiguous results where
there is underground congestion — the technology cannot positively identify multiple
adjacent buried facilities.
“We determined that a better method was required for marking
and locating underground cable routes, and eventually we adopted buried markers
because they are safe from surface threats, require no maintenance, and provide
very precise locating,” said Murphy.
“We initially used passive markers, which indicate location
only, but have settled on active identification markers that can be programmed
with specific information about the location when they are placed, and then
read later from the surface using an electronic locating device. Unlike
traditional locating, buried markers allow the locator to easily distinguish
between adjacent facilities and make it possible for crews to excavate safely
even under crowded underground conditions.”
UNDERGROUND GUIDLINES
Underground utility markers conform to a national utility
color code and interrogation frequency standards for each utility type so that
excavators can identify both the location and the nature of buried facilities.
FAA is placing red markers for facility power cables and black/orange markers
for fiber optic and other communication cables at the Atlanta location.
FAA engineers selected the 3M™ Dynatel™
2200MiD Series Locating and Marking System for the Atlanta airport project. This marking system
uses 4-inch round ball markers, each of which has a unique, preset, and
remotely readable ID number. An electronic circuit in the ball is programmed
with custom information, which can then be located and read remotely. Murphy
explains that FAA has developed a series of scripts for ball marker programming
that includes details such as the nature of the buried facility (cable type,
number of conductors or fibers, etc.) and the exact depth below grade. FAA has
established 30 such identifying scripts, covering every combination of details
for their buried facilities at the airport. Program and placement details for
each marker are archived in the locator device as they are programmed, and
these records are downloaded electronically at the end of a shift for
archiving.
“An above ground locator can pinpoint the position and depth
of an electronic marker so precisely that it is possible to dig down and find
the ball with a posthole digger,” says Murphy. “Traditional locating equipment
relies on an electrical return signal from a conductive element such as a pipe
or cable and can provide only an approximation of location. Ball markers will
help protect critical buried FAA infrastructure, and make it very easy to
pinpoint and excavate a buried segment or discrete point in the future.”
According to the FAA project engineer, marker placement at
the Atlanta
site has been done by a resident FAA engineer working in conjunction with cable
placement crews. The engineer scripts each ball using the portable locating
device and places it in the cable trench as work proceeds. Murphy’s staff is
currently developing a specification for this process. Future scripting and
placement work will be done by contractors in accordance with this document
under the supervision of FAA field inspectors.
“Construction work around active runways is done at night to
minimize flight disruption,” Murphy explains. “We position the markers at
200-foot intervals for long cable runs and at turn points, at intervals around
curves, and ten feet apart in congested areas and around manholes. Both sides
of every buried utility road crossing are also marked. As each marker is placed,
its identifying label is removed and placed on a field map. These marker radio
frequency identification (RFID) numbers will eventually be transferred to
as-built drawings for site mapping and for reference by construction crews and
field engineers.
“There may be a need in the future to extend airport
taxiways, add turnoffs, or replace equipment, and this work will benefit from
the precise underground records and locating capabilities we have established
during construction,” he says. “However, our principal motivation for this
marking and locating investment is to avoid construction-related wire and cable
cuts, which are extremely costly and present unacceptable safety risks and
airport delays.”
HIGH VOLTAGE CABLES
Another project currently underway at Atlanta’s Hartfield-Jackson
International is placement of new underground high voltage power cables on the
airport’s south side. Bob Blanchette, FAA project
engineer responsible for the project, notes that cable replacement is being
done to upgrade the old power distribution network that serves dispersed
navigational aids. Existing cables are 30 to 40 years old and suffer from
splice failures, maintenance problems, and vulnerability to power surges and
lightning damage.
“There will be about 30,000 feet of new cable installed in
this effort, as well as new switch gear and transformers to support
navigational aids, including instrument landing systems, precision approach
path indicator, and runway visual range systems,” says Blanchette.
“Cable runs are point-to-point and laid in straight
lines wherever possible, with RFID markers placed at either side of each
intermediate manhole, on each side of every system facility, and every 200 feet
along straight cable runs.”
FAA has informed the Airport Department of Aviation of this
construction and marking project, and will share information on infrastructure
marking with airport crews and authorized contractors for mutual benefit.
The marker locator used for this work and for the runway
addition has a GPS feature that allows for automatically collecting GPS
coordinates for markers as they are buried. GPS information can be placed in
the mapping database along with marker locations and other infrastructure
details. GIS mapping will eventually show all underground facilities, including
global coordinates for each marked location, and help ensure that future
excavation, maintenance, and construction work will not compromise worker
safety or the integrity of airport facilities.
Unlike surface markers, such as stakes, flags, or paint, a
buried RFID marker is not affected by overgrown vegetation or maintenance
equipment and can’t be worn away by weather. Markers act as passive antennas,
reflecting back the query signal from the locator without need for an internal
power source. They are impervious to moisture, minerals, chemicals, and
temperature extremes. Internal components are self-leveling, ensuring that they
will always be in a horizontal orientation for best signal strength regardless
of how the device is placed in the ground.
One Atlanta
airport challenge that will be relieved by the use of identification markers
and mapping is the problem of unmarked and abandoned cables, Brian Murphy
explains. For example, in the past, a fire rescue building located on the north
side of the airport was served by a number of undocumented cables buried at
shallow depths. The presence of cables such as these slows construction process
as crews must take precaution to confirm that lines encountered during cable
placement are not in service. Properly marked and mapped facilities will
prevent this problem in the future.
“Fiber optic cable replacement efforts are planned or
underway at many of the major commercial airports in the FAA’s southern
region,” says Murphy, “and we have adopted RFID markers for all new buried
infrastructure work.”
Reprinted with permission from Airport Business magazine • June 2006
3M Communication Markets Division
800-426-8688
www.3M.com/Dynatel
