Without reliable lighting systems to facilitate aircraft movements, flights can be delayed or canceled, causing an onerous ripple effect for travelers, businesses, and airlines alike. Worst case, an incursion can occur at an active runway intersection with a potential for fatal results.
The Architecture of Airfield Lighting Control Systems
Lighting infrastructure on the airfield includes runway and taxiway edge lights, threshold lighting, airfield guidance signs, and apron areas where aircraft are loaded and refueled. Power is distributed to the lighting circuits by underground cables from electrical vaults installed at selected locations on the site. These vaults contain the power distribution equipment for the lighting circuits, and are controlled by an Airfield Lighting Control & Monitoring System (ALCMS).
Liberty Airport Systems, an Ontario, Canada-based equipment manufacturer, holds over 30 years’ experience designing airfield lighting power and control systems, including those for airports in Houston and Toronto. They’ve seen it all and understand the consequences of failure of the lights airside.
While Liberty’s power and control system solutions are application-specific, the core hardware and software products employed in their system design remain constant. At the heart of each ALCMS system are Rockwell Automation® ControlLogix® Programmable Automation Controllers (PACs). Lighting circuit status is served to a FactoryTalk® View Supervisory Control and Data Acquisition (SCADA) operator console located in the Air Traffic Control Tower, providing Federal Aviation Administration (FAA) Controllers with a touch-screen interface from which they control the various lighting circuits on the airfield. Fiber optic cable is used as the primary communications medium. In many cases, a secondary parallel fiber network is installed as a backup.
Independent Wireless Redundancy
Airports are a dynamic entity, with runway and taxiway expansions and surface rehabilitation ongoing. Construction and maintenance airside is a common event, whether for new construction or maintenance purposes. With fiber optic cable runs all around, there exists the risk that the fiber can be damaged during construction and the control system will be knocked offline.
As industrial wireless solutions began to emerge, Liberty considered their distinct advantages as backup communications to the fiber lines. Cost reduction associated with installation, maintenance, and replacement of fiber was a major driver, but even more valuable was the assurance of increasing uptime by implementing an independent backup communication system.
“Uptime and maintenance aspects are a huge consideration. If the system goes down, a maintenance team must be brought in. The costs of this can be significant, particularly if the occurrence is at night or on a weekend. But, if the system is able to automatically switch over to the wireless backup, this cost is avoided,” says Tom Wodzinski, Liberty’s Control Systems Product Manager.
Reaching Remote Sites
In a majority of airside projects, site equipment is deployed over a large physical area. Locations may involve a few I/O points and remote operator consoles which are potentially distributed over distances up to five miles. In these situations, it’s often not economical to run fiber and wireless becomes the primary line of communication.
In fact, Liberty has standardized on wireless as the primary network for the more distributed applications on the airfield, including control from Central De-icing Facilities. De-icing is essential to safe aircraft operation in winter. An anti-freezing agent called glycol is used for this process. Because of its toxicity, environmental regulations now require modern airports to designate an area for the de-icing process, where glycol used to spray the planes is collected into reservoirs, cleaned and discharged. These de-icing facilities are generally remote from the main terminals, so independent lighting systems are used to guide planes into the appropriate bays for spraying.
Mobile Connectivity, Maintenance, and Transferability
To take things one step further, the Winnipeg International Airport’s Central De-icing Facility lighting is controlled by a mobile laptop PC using a high-speed wireless EtherNet/IP communications module. The lighting infrastructure of de-icing pads resembles a mini airport, where an individual called the Iceman controls the movement of aircraft within the de-icing area. The Iceman’s mobility is quite important as he moves about the facility and guides aircraft in and out under the most severe winter conditions.
If a runway is closed for maintenance, airport electricians can roam the airfield performing mandatory light checks while manually controlling each circuit from their mobile wireless computer. In the past, they would have had to contact the tower to switch circuits on/off for them, a tedious and time-consuming procedure at best.
Wireless communications has proven to be very successful, but not without its challenges. “When you run fiber, you dig a trench and put it in the ground,” Wodzinski said. “You know it’s there. With wireless the biggest difficulty is pinpointing a point of interference if, for example, the airline implements an overlapping unrelated wireless network in the terminal. We can’t control who else is in the spectrum tomorrow.”
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