San Diego Int'l Switches to LED Runway Status Lights

Despite the best efforts of air traffic controllers, pilots and ground support staff, runway incursions can still occur. One of the FAA's frontline strategies to help further reduce incursions - Runway Status Lights (RWSL) - took another step forward in November, when the system at San Diego International Airport (SAN) was updated with LEDs.

For SAN, the change to more energy-efficient fixtures dramatically reduces operating costs and maintenance requirements. For the FAA, it marks an important refinement in the pilot program that placed prototype systems at four major airports throughout the country: Dallas/Fort Worth International, Los Angeles International, Boston Logan International and SAN.

Each of the original facilities was selected because it presented a unique operational challenge. "We were solving different parts of the overall problem at each different airport we went to," explains Peter Hwoschinsky, FAA program manager for Research and Development for Human Factors and Operations. "San Diego was chosen because it had a single runway environment with difficult approaches and also had only an ASDE3 system, just the skin tracking radar, and we were curious how well it would work. And it works very well."

A subsequent production version of the RWSL system is being implemented in 23 airports across the United States. Claude Jones, FAA project manager of the production system, is working with the airports and Saab Sensis to get the system up and running.

The overall program, notes Hwoschinsky, dates back to the early 1990s, when MIT Lincoln Laboratory developed the concept of using surface surveillance radar to improve runway safety and began testing the use of red "wigwag lights." The fully automatic RWSL system

that eventually evolved from the idea was engineered to reduce the number and severity of runway incursions while not interfering with airport operations. It works in conjunction with three technologies: airport surface detection equipment (ASDE), the surface radar that uses primary radar to "skin track" aircraft; airport surveillance radar (ASR), which tracks aircraft in the air down to about 200 feet and in some instances even on the surface; and transponder multilateration, secondary radar that receives signals from aircraft with information about their identify and location.

"Using these three types of radar, we figure out the position of the aircraft and its movement relative to other aircraft that are moving or holding still and figure out whether or not there is a conflict or whether there might be if someone were to continue," explains Hwoschinsky. "Based on that information, we turn on or turn off red lights to indicate the presence of either high-speed traffic or traffic that might be in conflict."

Involving a variety of stakeholders and end-users early in the development process helped create a successful system, he relates, noting that the FAA sought input from pilot organizations, airport operators, aviation industry groups and academia. "(We also) completed a safety risk management process before it was even institutionalized within the FAA because we involved flight standards, air traffic, airports and the runway safety office," he adds. 

Making the Switch

When SAN's original incandescent RWSL system was installed in 2007, the airport's role in the process was clear, recalls Dean Robbins, SAN manager of airside operations. "The FAA came to us with the understanding that this was entirely their system and that we would help facilitate the installation of the system, which we did," explains Robbins. "They did all the installation, maintenance and everything else associated with the project."

The system was subsequently taken offfline for approximately 18 months during a major taxiway rehabilitation project on the north side of the airfield. More recently, the incandescent system was replaced with an LED-based system in November 2011. 
FAA contracted GEMS to issue the request for qualifications, evaluate suppliers and mange the recent conversion project. LED technology provided multiple advantages, notes GEMS' senior airport lighting engineer, Seward Ford.

An incandescent system needs to be energized 24 hours a day, seven days a week and requires constant monitoring for lamp failures, he explains. "Even when the lights weren't on, the circuit had to be on to power the individual light control device that once it received the signal, it would turn the lights on and monitor the light," relates Ford.

Incandescent lamps "bloom up" when they turn on and diminish when shut off, adds Hwoschinsky. Turning on takes about half of a second, and turning off takes another three-quarters of a second. In contrast, LEDs turn on and off almost instantaneously. At SAN, eliminating the small time delays added up to big savings.  

"We are down to using about 10 to 15 percent of the power the incandescent system used before," reports Hwoschinsky. "So we save power, the LEDs are going to last a lot longer than the incandescent and they will not diminish in their light output as fast as the incandescents do."

Another difference between LED and incandescent lamps is their typical mode of failure. The filaments of incandescent lamps ultimately fracture with regular usage and light output abruptly ends. "At one moment we had an acceptable light source and the next moment we had nothing," describes Ford. Because of this, systems with incandescent lamps must also monitor for lamp failures or lights not turning on when they should.

With LEDs, light output gradually reduces over time. "After many thousands of hours of use, the light output eventually drops off to a point that it is no longer useful for the intended purpose," he contrasts. Due to the typical LED mode of failure, constant monitoring for instant, catastrophic lamp failure is not needed.

"The SAN RWSL system is the first design to take this approach that results in a reduced installation cost," notes Ford, adding that the FAA still periodically inspects each circuit for unexpected fixture failures. At SAN, such checks are completed every two weeks. "Up to this point, there have been no LED failures," reports Ford.

Liberty Airport Systems provided the design and system integration of the airfield lighting equipment in the electrical vault and on the airfield. Standard FAA L-829 lamp outage monitoring was used to detect the failure of any fixture on a circuit, eliminating the need for expensive SMGCS-style single lamp monitoring used in first-generation RWSL systems, notes Liberty Airport Systems vice president of sales, Don Gordon. In addition, threshold LED lighting segments were switched on/off using conventional group circuit selector switches in lieu of single lamp controllers. The savings on equipment and installation were tremendous relative to the older style single lamp controller systems deployed earlier, reports Gordon.

Results

According to Gordon, switching to an LED RWSL system that doesn't require single lamp controller hardware and halogen lamps has reduced maintenance requirements at SAN by 95%. In addition, energy costs were reduced by 50%.

 
"Liberty's technical solution was critical to the project's success," notes Gordon. "It was imperative that the system we designed worked as intended the first time."

The GEMS team made the project flow smoothly by coordinating the various project participants, he adds.

For the FAA, the ultimate value is in the system's effectiveness. "First of all, it work," notes Hwoschinsky. "People stop when they see red lights."

"It really enhances safety," agrees Robbins. "It's just another visual tool for the people operating (ground support) vehicles to know that the runway has an aircraft that's on it or about to be on it. It's just really another enhancement tool for airport safety."
For more information about runway status lights, visit: http://www.faa.gov/air_traffic/technology/rwsl/ and http://www.rwsl.net/