We all do it. Gaze out oblong windows from seats in their upright positions; feel the deceleration of the plane as it floats down the glide slope of the approach; watch our smooth descent toward two retreating columns of light defining the runway ahead. It is part of the experience of flying and much of your personal safety rests on the reliability of the airfield lighting systems that serve as the pilots’ visual aids during take-off and landing.
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.
“If a network communication problem means a major airport cannot control the approach and runway lighting, the airport may be forced to delay or divert the flights. That’s a big deal,” says Liberty President Allan Fletcher. “That’s why we use robust industrial-grade products and multiple levels of redundancy in our control system products.”
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.
FactoryTalk View is part of a unified suite of monitoring and control solutions designed to span stand-alone machine-level applications up through supervisory-level Human Machine Interface (HMI) applications across a network. This suite offers a common development environment and application reuse such that system engineers can improve productivity while helping clients reduce maintenance costs and improve airfield safety overall.
Fiber optic cable is used as the primary communications medium. In many cases, a secondary parallel fiber network is installed as a backup. While reliable, fiber-based communications does have shortcomings, field conditions may be such that:
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.
Liberty had been using Wireless Ethernet products successfully since the late 1990s, but began to experience problems as the amount of multicast I/O traffic on their network increased. After some research and consultation with the automation group at Gerrie Electric Distribution, Liberty discovered that ProSoft Technology’s Industrial Hotspots were better able support their application needs.
“Liberty is an exciting company to work with because they are highly innovative, always seeking new and better technology,” comments Rob Porter, Automation Product Manager for Gerrie. “When ProSoft Technology released these radios, which were specifically designed and optimized for EtherNet/IP, it made for the right solution and Liberty was quick to take advantage of it.”
“We went with ProSoft because they are able to handle high multicast traffic, and upon using the radios we also found the configuration tools were much more simplified,” Wodzinski said. “From our standpoint as a system integrator, we were able to reduce development and installation costs because we could employ the same local electrical contractors that perform the installation of our electrical equipment to mount the data radios.”
Seamless Transition to Backup Communication
In one installation, Liberty supplied the airfield lighting control system to the Canadian Forces Base in Trenton, Ontario. CFB Trenton is a military airfield providing deployment support for military and humanitarian efforts around the world. The basic system relies on wireless backup for the ALCMS functions. In a later system expansion, eight new Rockwell Automation POINT I/O™ drops were added to the wireless network, providing real-time control and monitoring of high mast apron lighting around the airfield. The cost to install seven wireless nodes to the network came in at less than half of the cost of a conventional hardwired configuration.
In June 2010, the unexpected did happen. A contractor dug through a major telecommunications duct bank containing the main fiber optic communication cables for the airfield lighting. Communications and airport operations continued flawlessly on the wireless radio network for the next week while new cables were procured and installed.
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.
Wireless mobile units are becoming common on the airfield, not just for de-icing but for mobile maintenance units, like one designed for Phoenix Mesa Gateway Airport. The airport uses ProSoft Technology’s IP66 weatherproof radios to communicate from the maintenance vehicles to the main control system locations including the control tower and two electrical vaults.
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.”
Jim Weikert, Wireless Strategic Product Manager, adds, “Interference is an innate concern with open frequencies. For these types of applications ProSoft Technology offers several options for monitoring network health. For example, OPC (an open standards specification) can be integrated into an HMI or SCADA system and through Simple Network Management Protocol (SNMP), which allows IT engineers visibility to network performance. In addition, ProSoft Technology offers alternative solutions at 900 MHZ, 2.4 GHz and 5.1 – 5.8 GHz bands, allowing the system to be tailored to work within the spectrum available.”
All in all, the benefits outweigh the costs for Liberty and their customers.
“We’ve had a very positive experience,” Wodzinski said. “ProSoft is responsive when issues arise during installation. The support guys are always very helpful, good to work with, and we can’t see building our systems any other way today.”
Learn more about ProSoft Technology’s wireless solutions here