A Project of Parallels

With both city and state owners responsible for taxiway work at Ada Municipal Airport, meticulous project management became vital to its success—especially when the $1.5 million realignment expanded into a $5.5 million enterprise.

On behalf of the City of Ada, the Oklahoma Aeronautics Commission (OAC) shouldered a project to realign and reconstruct the parallel taxiway for Runway 17-35. The original asphalt taxiway was constructed on a radial geometry—a non-standard configuration. Rather than running parallel to Runway 17-35, it moved diagonally away from the runway and incorporated an unusual arc at its midpoint to circumvent the terminal apron. This created several oblique intersections and safety area encroachments. In certain areas, pilots taxiing in high-wing aircraft couldn't see approaching aircraft prior to crossing the runway.

Garver provided planning, design and construction administration to straighten the taxiway and rehabilitate deteriorating pavement sections due to subgrade failure and increased traffic loads. In addition, Garver managed the coordination between the City of Ada and the OAC. This was the Commission's first time contracting directly for engineering, testing and observation services for a project not associated with state property.

"This really was a unique situation," said Garver Project Leader Curtis Brown. "The Commission used this project to improve the way it manages its own projects. We established clear communication measures between the City and the Commission to make sure the two parties continued to head in the same direction."

Because of the two-entity ownership, Garver increased its conversations and meetings, and duplicated its paperwork to keep the clients informed of design decisions and construction progress. This became particularly relevant when Garver identified a conflict in the existing taxiway's layout.

"During the design, we discovered that the existing taxiway was a primary surface violation for Runway 17-35," said Garver Project Designer Todd Hebert. "The runway is the center point of every airport, and within certain distance parameters, nothing can be higher than the runway centerline. We discovered that the taxiway rose above the runway and needed to be lowered by nearly 3 feet in some areas."

Although the taxiway's ends were level with the runway, the pavement gradually climbed 30 inches above the runway. Having previously provided planning services, Garver understood that Ada Municipal Airport planned to seek FAA approval for precision approaches. This rise above the runway created a TERPS surface and Part 77 encroachment that impacted the airport's ability to receive better than 3/4-mile minimums on a vertically guided instrument approach.

"It was important to correct the taxiway's vertical alignment so that the airport could receive additional approaches to attract larger planes and more clients," Hebert said. "If we hadn't caught that conflict, the airport may have realized they had a primary surface bust only when pursuing those future precision approaches."

To correct the taxiway, the project needed an additional $4 million and a second year of construction to receive the needed state and federal grant funds.

"Lowering the taxiway caused us to rework the entire terminal apron, make adjustments to the electrical system, and reconstruct the fuel farm," said Brown. "Due to the additional cost, it took a month of intense communication between the FAA, OAC, City of Ada and Garver to determine the most economical solutions that met aviation standards."

Garver divided the project into two phases. The taxiway and associated asphalt and concrete pavements were completely removed, and the utilities, electrical system and storm drainage relocated to lower elevations. Construction crews then excavated down to the new subgrade level and installed a thicker concrete taxiway pavement.

In addition to replacing the airfield's electrical vault and installing medium intensity taxiway lights along the full length of the new parallel taxiway, the airfield development includes cutting-edge light-emitting diode (LED) taxiway signs.

"This is Oklahoma's first application of LED airfield signs," Brown said. "Ada Municipal Airport will use a complete LED system as part of its new taxiway."

While the project was being bid, Garver Electrical Engineer Bart Gilbreath received information that a new airfield technology was available—LED guidance signs. After investigating the financial cost and benefits of LED signage, Garver received approval from the OAC and City of Ada to modify the plans to install Siemens Airfield Solutions' LED signs.

"The cost of buying the more-expensive LED signs was justified by the lower power equipment required in the electrical vault," Gilbreath said. "The system requires constant current regulators to power the equipment in the airfield. Because we went with the LED signs, we were able to use regulators with lower kilowatt ratings, dropping the equipment cost significantly."

Besides reducing energy usage by 50 percent and providing 50,000 hours of lamp life, the LED signs will save maintenance costs and time.

The Oklahoma/Arkansas Chapter of the American Concrete Pavement Association recently honored Phase 1 of this project as a Silver Winner. The award recognized the project's high-quality finish, uniformity, airfield benefit and workmanship quality.