Each year, approximately two million commercial flights depart or arrive in Canada and ten million in the United States, report Statistics Canada Transportation Division and the Bureau of Transportation Statistics respectively. Without reliable lighting systems to facilitate aircraft movements, flights can be delayed or cancelled, 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. Liberty Airport Systems, an Ontario, Canada-based equipment manufacturer, provides some interesting uses of wireless communication as a runway lighting backup to a primary fiber optic network.
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 one’s personal safety rests on the reliability of the airfield lighting systems that serve as the pilots’ visual aids during take-off and landing.
Airfield Lighting Control System Architecture
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 holds over 30 years experience designing airfield lighting power and control systems, including those for George Bush Intercontinental Airport in Houston and Toronto International Airport.
“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” says Liberty president Allan Fletcher. “That’s a big deal; 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 to 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. However, reliable, fiber-based communications can have shortcomings. Field conditions may be such that:
- Airside construction can compromise communications and thus operations.
- Communications duct banks lay under concrete slab runway and taxiways, which are very costly to install and maintain.
- Redundant fiber networks normally run parallel to the primary line, and thus are subject to common risks, especially when a duct bank is compromised by a negligent back hoe operator.
Independent Wireless Redundancy
Airports present a dynamic environment, with runway and taxiway expansions and surface rehabilitation ongoing. Airside construction and maintenance are common events, whether for new construction or maintenance. 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 in use 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,” says Liberty’s control systems product manager Tom Wodzinski. “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.”
Liberty has been using Wireless Ethernet products successfully since the late 1990s, however it 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 2.4 GHz Industrial Hotspots were better able to support their application needs.
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,” says Wodzinski, “ ... and upon using the radios we also found the configuration tools were much more simplified. 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 (CFB) 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 back up for the ALCMS functions. In a later system expansion, eight new Rockwell Automation POINT I/OTM 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 deicing facilities. Because of the toxicity of the anti-freezing agent glycol which is used in the deicing process, environmental regulations now require 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 deicing facilities are generally remote from the main terminals, so independent lighting systems may be used to guide planes into the appropriate bays for spraying.
Mobile Connectivity and Transferability
To take things one step further, the Winnipeg International Airport’s central deicing facility lighting is controlled by a mobile laptop PC using a high-speed wireless EtherNet/IP communications module.
The lighting infrastructure of deicing pads resembles a mini-airport, where an individual called the Iceman controls the movement of aircraft within the deicing 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 deicing but for mobile maintenance units, like the 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 and 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,” says Wodzinski. “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.”