Of all the ground facilities in aviation’s total infrastructure, few are more interesting than airport control towers. Whether serving smaller communities or large metroplexes, airport towers provide one of the best close-up views of our industry, second only to flying itself.
Avionics Magazine recently visited two Nav Canada towers, representing both ends of the industry spectrum. One, in Toronto, handles a substantial number of movements, composed mainly of airline jets and turboprops, arriving from and departing to domestic, U.S. and overseas destinations. The other air traffic control (ATC) tower, in Vancouver, on Canada’s west coast, handles just domestic single- and twin-engine fixed-wing piston and turboprop commuters and private aircraft, plus helicopters. You could say they represent the big and little leagues of aviation.
Yet while the two towers are quite different in size and activity levels, controllers and pilots using their facilities operate on the same basic set of procedures, rules and communications protocols that form the foundation of ATC around the world. After all, the private pilot flying a Cessna in Vancouver could one day move up to a smaller commuter airliner and, in time, rise to command an intercontinental jet transport.
Opened in 1998, the $17.2-million (Can./$10.9-million [U.S.]) control tower at Toronto’s Pearson International Airport is Canada’s busiest, handling some 400,000 aircraft movements a year. Situated in the airport’s center and surrounded by five all-weather runways, each with an instrument landing system (ILS) at either end, the 214-foot (65.2-meter)-high structure is Nav Canada’s showpiece facility. The tower operates 24 hours a day with a staff of 40 and embodies the latest in technology, all of which has been developed in Nav Canada’s engineering laboratories in Ottawa, with strong emphasis on commercial-off-the-shelf (COTS) products.
Perhaps the most notable COTS technology is the Integrated Information Display System (IIDS), which might be described as Nav Canada’s central nervous system, linking ATC centers, control towers and other key facilities. IIDS is basically an expandable host computer system, supporting 10 different software applications, covering all aspects of air traffic control (see sidebar).
To the visitor, the most apparent of these applications is Nav Canada’s extended computer display system (EXCDS). Its touch-screen controller displays and interfacility data transfer capabilities have revolutionized tower and control center operations. The data is transferred via very fast wide and local area networks (WANs and LANs). Should one controller submit a comment or instruction–say, a reclearance–for a particular aircraft, he or she touches that aircraft’s record on the IIDS screen and the comment/instruction goes instantly and automatically to all other controllers in the system who are involved with the aircraft.
Hand-written notes on individual aircraft paper routing strips have long since disappeared from use at the eight workstations at Pearson International, as have the virtually continuous voice exchanges between tower controllers and the nearby control center and other airport facilities. "Sometimes, it gets eerily quiet up here," said one controller, "even though everything is running normally."
Voice communications still exist at Pearson–the tower’s voice switch is made by Frequentis. But the objective is eventually to offload voice channels and limit voice communications to urgent messages. In fact, 70 percent of aircraft clearances and most interpositional communications already are data-linked.
EXCDS also offers controllers a wide choice of screen presentations, such as:
Runway and taxiway movements;
Flight plans and clearances, from air traffic operations;
Lighting (controlled from the tower);
Slot assignments and flow control data, from the traffic management unit; and
EXCDS includes a variety of other information, as well, including the airport’s automated surface detection equipment (ASDE). The ASDE fuses inputs from two separate surface surveillance radars to provide a total airport mosaic of ground movements. (Pearson had three surface surveillance radars but one recently was decommissioned.) The inputs are updated at least once per second.
Controllers receive automatic aural and visual alerts when surface surveillance radar detects aircraft and ground vehicles on a runway while another aircraft is on an approach. Tower controllers also are alerted of taxiing aircraft that are predicted to enter an active runway.
Any screen presentation can be instantly called up with the touch of a fingertip and, just as easily, tailored in scale. Airport surface diagrams, radar coverage, weather maps, etc. can be made larger or smaller, according to controller preference. The screen can be tailored in orientation, as well; controllers can rotate the presentation for a view in any direction.
Nav Canada’s Toronto facilities alone have more than 100 EXCDS workstations which, in many ways, offer significantly more advanced technology than the "glass cockpits" on the flight decks in many of the aircraft that use the airport.
In daily operation, the tower frequently operates as two separate towers, controlling the separate traffic streams to its two main east/west runways. This is due to the airport’s unusual configuration, where the two runways are two miles (3.2 kilometers) apart, with the tower situated between them. Tower controllers at Pearson therefore face opposite directions and operate totally independently of one another.
But even with this flexibility, increasing traffic volumes have demanded an additional east/west runway, which parallels one of the earlier main runways. To cope with peak traffic volumes, the tower has a unique movable and rotatable controller’s position, located in the center of the tower cab. Capable of facing north one day and south the next, the position, which is on castors, can be used as a backup to other controller stations.
Coming shortly to the Pearson tower is a converging runway display aid (CRDA), designed to achieve maximum landing rates through minimum spacing. The CRDA takes in radar data and, with an aircraft performance database, automatically computes and displays the projected future positions of aircraft approaching to land. An aircraft’s projected position appears on the tower controller’s screen as a "ghost" image, which moves in accordance with the aircraft’s movement.
Developed by Nav Canada engineers from a Mitre Corp. prototype, CRDA allows controllers to see instantly whether safe separation will be maintained through touchdown.
A multilateration system, which uses transponder "tags" to provide faster and much more precise tracking of aircraft in the terminal area and on the ground, probably will be installed, as well. This despite the fact that Nav Canada controllers have expressed concerns over the excessive clutter produced by an abundance of transponder tags, on an earlier system that was tested in 2001. Undoubtedly, Nav Canada’s innovative engineers already are thinking about how this issue can be resolved.
Growing from the grass-surfaced Malton aerodrome of the 1930s, Pearson airport and its advanced control tower have unquestionably placed Toronto into aviation’s Big League.
Nav Canada’s control tower at Vancouver Harbor (not to be confused with Vancouver International, the major airline hub several miles to the south) is a very different environment from Toronto-Pearson. Here the task of the tower’s nine-person staff is the dawn-to-dusk control of traffic at the seaplane aerodrome in Vancouver Harbor.
The Vancouver Harbor tower has just one workstation, yet it is a real tower, typically overseeing some 60,000 landings and takeoffs, plus about 35,000 overflights, per year. Almost all are commercial movements, roughly 60 percent of them, float planes. The balance largely is helicopters, which arrive and depart from a four-pad heliport, just off the shoreline. Overflights include sightseeing tours, banner tows and, on weekends, recreational fliers. The flights also include movie shoots, the result of Vancouver’s seeming transformation in the summer into "Hollywood North," with sound trucks and miles of cable snaking along the waterfront streets. Vancouver Harbor is a busy airport but not fast-paced. It averages about 90 movements a day in the winter and 150 daily in the summer.
The fixed-wing traffic runs the gamut, from small Cessnas to Twin Otters, with an occasional Beaver, Otter and rare birds like Noorduyn Norsemen adding spice to the mix. This fixed-wing traffic is paralleled by scheduled Sikorsky S-76 passenger operations that, with more than 25,000 annual helicopter movements, make the harbor’s heliport by far the busiest in Canada. In fact, the harbor tower is probably setting other aviation records, when the total number of fixed- and rotary-wing movements is compared to the small volume of airspace it controls, i.e., 12 by 4 miles (19.3 by 6.4 km), from zero to 2,000 feet.
But, while the tower was commissioned in 1978, Nav Canada has ensured that it stays on the cutting edge of new technology. For example, it has touch-screen communications technology identical to that installed at Toronto-Pearson’s tower. Vancouver Harbor is equipped with both IIDS and EXCDS, like Toronto-Pearson, although they include fewer features. And, also like Toronto-Pearson, the harbor tower has a radar display linked to the local control center’s radar, although this is used by tower controllers for traffic monitoring and does not provide conflict resolution or vectors. Automated terminal information service (ATIS) also is provided and, although the harbor has no dedicated navigation or approach aids, it does have two public GPS non-precision approaches plus nine private GPS procedures assigned to the local commercial operators.
There’s no inferiority complex towards big league towers among Vancouver Harbor controllers. They claim two advantages that their Toronto brethren can never enjoy. The first is their spectacular location. Upon entering the harbor control cab, visitors are overwhelmed by its 360-degree panoramic view, with the city of Vancouver spread out behind, Pacific-bound vessels moving out to the west, snow capped mountains to the north and, directly below, Alaska cruise ships loading and unloading tourists at 2,500 passengers a clip. The key to the breathtaking view is the tower’s location, atop one of the city’s highest office buildings on the harbor shoreline. As one official joked, "This is the best view in Vancouver. If we charged tourists $10 a head to come up here, we’d make millions."
The cab’s perch makes the Vancouver Harbor tower higher than Pearson’s. Such a vantage point for controllers, plus the light traffic, negate the need for any surface management tools. Weather can put the tower into instrument meteorological conditions (IMC), but such conditions would preclude any movements at the airport, as well.
Vancouver Harbor controllers are amused by the U.S. Federal Aviation Administration’s claim, in October 2002, that the newly opened, 345-foot (105-meter)-high tower at Orlando Airport had become "the tallest control tower in North America." They politely suggest that to merit the "tallest tower" title, Orlando would have to grow at least another 120 feet (36.5 meters) to beat the harbor tower’s 465 feet (141-meters). But they don’t bear a grudge. They simply call this the highest tower in the world.
Nav Canada is understandably proud of the Extended Computer Display System (EXCDS), a non-verbal tower-terminal coordination device that makes the operations at tower control and terminal control paperless. EXCDS, pronounced "exceeds" by controllers, is one of 10 software applications hosted by the Integrated Information Display System (IIDS–host computer). The others are:
Computer Visual Information Display System, which presents approach charts, maps, manuals and other graphical material;
Operational Information Display System, which shows airport and meteorological data, navaid status and approach information;
Air Traffic Flow Management System, which presents flow status information, bedpost and runway data, and provides flow messaging;
Nav Canada Radar Display System, a PC-based radar display system that includes the converging runway display aid;
Clearance Delivery List, which shows oceanic, clearance delivery information from the Gander (Newfoundland) Automated Air Traffic Control System (GAATS);
Power Terminal, the terminal interface from GAATS;
Airfield Lighting Control System, which controls airfield and stopbar lighting;
Nav Canada Aircraft Movement System, which records aircraft movements for billing, statistical and information purposes and refers these movements via e-mail to the requesting agencies; and
Digital Automatic Terminal Information Service, which records airport-specificinformation in digital format and sends it via ARINC protocol to the cockpit.