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Friday, October 1, 2004

Cape Verde: Modernized ATM in the Mid-Atlantic

An unusual ATC environment integrates oceanic and continental air traffic management into a single system. Islands off Africa's western coast are equipped with surveillance radar, as well as for CPDLC, ADS-B and FANS 1/A.

George Marsh

Three hundred and twelve miles (500 km) off the bulge of western Africa lies a group of volcanic islands that were once a vital stepping stone for piston-engine airliners crossing the Atlantic between Europe/Africa and South America. The nine major Cape Verde Islands and several islets, together, are only a little larger than Rhode Island. But this statistic belies their continued strategic importance. For these dots of land, once owned by Portugal, lie within the busy Europe/South America (EUR/SAM) corridor frequented by today's passenger jets. Five designated EUR/SAM routes traverse the islands' flight information region (FIR). These routes, in turn, are crossed by another route linking Africa with Central and North America.

The Sal FIR, named after the island of Sal, home of Cape Verde's main international airport, borders the African continental Dakar FIR to the east, the Canary Islands FIR and Portugal's Santa Maria FIR to the north, and extends out into the ocean towards Brazil. The large volume of flight movements in the FIR--some 27,000 per year and growing--plus a need to control aircraft in the Sal terminal area, meant that existing procedurally based air traffic services (ATS) were becoming inadequate. This was the stimulus for a major upgrade that represents the first ATS system designed for both oceanic and continental air traffic management. The Airport and Air Navigation Authority of Cape Verde (ASA) initiated the upgrade, selecting Indra ATM Sociedad Limitada as the prime contractor.

At the heart of the change is the introduction of radar and automatic dependent surveillance-contract (ADS-C), which allows controllers to "see" approaching aircraft. (Control previously was exercised through radio communications only.) The new system also allows for the future use of automatic dependant surveillance-broadcast (ADS-B), adding air-to-air capability to ADS-C's air-to-ground data transfer. ASA decided that its new surveillance sensors would be combined with high levels of machine intelligence, so that controllers would have maximum situational awareness along with the latest in ATM automation to assist them in their task.

After a bidding process, the authority selected Indra ATM, a seven-year-old joint venture between Raytheon in the United States and Spain's Indra Systems. Indra ATM is the prime contractor for the new air traffic control (ATC) system, dubbed SISTASAL. The project is nearly complete. In an unusual development in late April, the system went into operation directly from its site acceptance tests. That was after the two-year program had remained on schedule throughout and met all its key operational requirements.

Achieving a capability consistent with Eurocontrol's vision for air traffic control convergence required an ambitious specification. Advanced situational awareness had to be provided for controllers at a new area control center (ACC) at Sal Airport, and data had to be networked to airports on two other islands, Sao Tiago and Sao Vicente. ASA wanted a system that would fuse data from radars, ADS-C, pilot reports and a future ADS-B system, compare the resulting tracks with those predicted in filed flight plans, and highlight any discrepancies. The system's data processing computer also would be required to examine 4-dimensional trajectories and predict possible traffic conflicts, and to generate electronics flight progress strips. A voice communications and control system (VCCS) was needed to manage communications for an increased number of controllers based at the islands' three primary airports.

According to Pedro Merino, Indra ATM project manager for the Cape Verde upgrade, attributes that put the installation near the ATM leading edge include:

  • An architecture adapted to the requirements of both ocean and continental area control,

  • An ability to support area navigation (RNAV) and free flight routing so that conventional fixed ATS routes can eventually be phased out,

  • A dual capability to operate with flight management systems (FMS) configured for future air navigation system (FANS-1/A) initially and the aeronautical telecommunication network (ATN) eventually,

  • A three-way ability to support radar, non-radar procedural, and ADS environments,

  • Support for controller pilot data link communication (CPDLC), reducing reliance on voice messaging, and

  • The ability to support radar approaches within the terminal control area.

The upgraded system has to cater both to high-flying en-route traffic in the oceanic FIR, and inward and outward-bound aircraft within the islands' terminal areas. Oversight is required of movements not only at the islands' three primary airports, but also at six secondary airfields. (While Sal, Sao Tiago and Sao Vicente have manned tower facilities, the other airfields offer an automatic flight information service [AFIS] only.) En-route system accuracy had to be consistent with a 10-nautical mile required navigation performance (RNP 10) standard and the 1,000-foot reduced vertical separation minimum (RVSM) already established within the airspace. Overall, ASA wanted a system that could showcase the latest communication, navigation and surveillance/air traffic management (CNS/ATM) technologies recommended by the International Civil Aviation Organization.

Situational Awareness

A core task was to introduce radar where none had existed before. ASA acquired three "surplus-to-requirements," secondary surveillance radars from the Spanish ATM organization, Aeropuertos Espa�oles Navegaci�n A�reia (AENA). Indra overhauled and upgraded these radars to its SSR IRS-10 standard. Radars have been installed on the western, eastern and southern islands of Santo Antao, Sal and Sao Tiago, to provide a multiradar environment.

Disposed as a large triangle, the three radars enable single radar coverage for aircraft still well out over the ocean. They also provide double radar coverage for aircraft approaching the terminal areas and then triple coverage for aircraft within a terminal area. This ensures augmented redundancy, as the need for surveillance integrity becomes more critical.

Radar outputs are networked via the Cape Verde telecommunications infrastructure to control centers at the three main airports, including the Sal area control center. All three radars were to be operational by September 2004.

Controllers view the surveillance picture on Barco flat-screen, thin-film transistor (TFT) displays that are viewable in daylight. These dominate ASA's advanced controller positions, including ATC sector and tower positions at the Sal area control center and tower positions at the two other primary airports. Executive and planner controllers work in pairs at the advanced controller workstations, which Indra has modeled on similar units serving AENA in Spain.

Each advanced workstation console has two individually controllable 2K-by-2K color displays made by Barco. It also provides each controller with an auxiliary display, used mainly for text data, and a touch-screen interface for operating the new voice communications and control system. Indra located these additional facilities to the sides of the main situation displays. A centrally placed, shared "last resource" VCCS panel provides access to emergency voice communications. Merino says the consoles are modular, simple to maintain and easily reconfigurable.

Controllers use two simulation controller positions to train in radar procedures. Trainees can be presented either recorded scenarios or a dynamic replica of the actual control environment. A separate position enables a training supervisor to create training exercises and evaluate trainee performance. The training and validation simulators can be brought into the operational configuration if required.

The main displays present controllers with a comprehensive view of the traffic situation. Aircraft target returns are tagged with identification, altitude and other information. Data from multiple radars and pilot reports is fused to provide aircraft tracking. Controllers have advanced flight management features at their disposal. For example, they can compare flight progress with ATC clearances and identify significant departures from filed flight plans. Overlays of aeronautical maps, restricted areas and weather graphics can be added to the display.

Flight progress is normally presented as on-screen electronic flight strips, though traditionally minded controllers who prefer paper strips have the option of printing these out. Current traffic situations can be extrapolated ahead to provide a view of what will develop if no action is taken. Controllers also can call up flight plan lists and selected flight plan data, including routes with estimated times and flight levels.

The human-machine interface (HMI) is based on windows, drop-down menus that provide multiple choices and initial suggestions, and target pointing and clicking. For commonality with systems used elsewhere, ASA's display system complies with Eurocontrol's operational display and input development (ODID) III and IV interface standards.

AirCon 2000

At the heart of SISTASAL is Indra's ATM AirCon 2000 ATC automation system. AirCon's core surveillance data processing system (SDPS) relies on functionality that first evolved from the Spanish ATC automation system (SACTA), and it embodies core radar data processing technology from Raytheon. Indra contributed its expertise in flight plan processing to the joint venture. The AirCon 2000 incorporates Indra's advanced flight data processing system (FDPS). Together, the surveillance data and flight data processing provide comprehensive intelligence on air movements and facilitate ATM actions.

The SDPS server performs radar and weather data processing, along with track fusion functions. This surveillance processor is also responsible for a range of flight safety tools including:

  • Short-term conflict alert,

  • Minimum safe altitude warning,

  • Restricted area intrusion warning,

  • Cleared level adherence monitoring,

  • Navigation integrity control, and

  • Detection of any route insertion errors by pilots.

The FDPS server supports the creation of "synthetic tracks," based on flight plan information and controllers' inputs. It processes flight plans and related incoming data -- aeronautical, meteorological, notices to airmen (NOTAMs), etc. The server also manages aeronautical fixed telecommunication network (AFTN) traffic and allows for manual correction of erroneous ATFN messages.

The AirCon 2000 automatically processes and distributes flight plans and manages repetitive plans. It analyzes planned routes, ensuring that they conform to clearances. And, from the same data, the system determines whether any medium-term traffic conflicts are likely.

The AirCon 2000 also calculates trajectories in four dimensions and updates estimated times of arrival. Flight plan progress data can be recorded as a basis for overflight billing and statistics. Flow planning functions include managing air traffic flow to match airspace restrictions and slot availability, along with avoidance of congestion. The system interfaces with adjacent control centers and manages handoffs.

The AirCon 2000 enables controllers to display a host of information, including flight clearances, altered departure times, and arrival estimates. They can manage CPDLC messaging, call up ADS contracts, and review full track and associated status history over the previous 24 hours. Facilities are available to record and play back surveillance data, flight plan data and controllers' actions.

Voice System

An Indra SDC 2000 digital voice communications control system located in the equipment room of the new Sal ACC supplies all ground-air and ground-ground voice communications for up to 16 controllers. Touch-screen displays on the main control and display consoles show system status and permit system control.

The VCCS incorporates independent subsystems for radio and telephony with multiple duplex communication channels, 124 of them radio and 124 telephone. It allows for pulse code modulated (PCM) and time division multiplexed (TDM) channels. A highly modular design makes it possible to extend or alter the system to suit the needs of future airspace resectorization. Distributed processing and dual-redundant hardware ensure a high level of system integrity.

An Indra Neptuno 3000 digital voice recording system enables controller dialogues to be recorded and played in tandem with associated data displays. Up to 128 analog input channels are available. Voice signals are digitized and compressed using a range of compression standards for maximum storage capability. Up to 2,560 on-line channel hours are stored on an 18-Gbit hard drive, with on-line backup via hot-removable, small computer system interface (SCSI) disk units. The Neptuno architecture is based on dual PC workstations.

An aeronautical message handling system (AMHS) and ATN router manage aeronautical messaging. The router provides connection to ICAO's ATN for air-ground and ground-ground segments, and to data link service providers. The system incorporates AMHS/AFTN conversion and processing functions. An ATS access router is compliant with CNS/ATN standard and recommended practices (SARPS). Dual configuration, along with hot standby and automatic switchover, ensures high system availability.

An Indra technical monitoring and control system provides oversight of all the main equipment's operating status, together with maintainer control and reconfiguration facilities. System parameters can be changed on line. The monitor and control system also can print out status and configuration details.

System Architecture

SISTASAL, in particular the central AirCon 2000, uses a dual Ethernet local area network (LAN)-based architecture. This ensures an open "future-proof" system that can readily be grown or modified to take advantage of advances in ATM technology. Use of commercial reduced instruction set computer (RISC) processors ensures that high system performance goes hand in hand with affordability.

Processing power is distributed throughout the system. For example, radar inputs are processed at the workstations. Dual-redundant servers, LAN and other hardware, with hot standby and automatic switchover where appropriate, ensure high availability.

In case of a radar equipment or network failure, the system can default to autonomous mono-radar operation via direct connection. Data can be switched between controller positions so that the loss of a single display or operator position does not disable the entire system.

SISTASAL incorporates the Unix operating system and software algorithms with self-recovery features. Commercial database technology and standard query languages facilitate database management, providing user-friendly access to adaptation data. Stored data on geography, reporting points, airways, aerodromes and aircraft types and performance all can be altered to take account of airspace and traffic changes.


Most of SISTASAL's major elements are housed in an equipment room on the ground floor of the new two-story 32,570-square-foot (3,026-m2) ACC building that ASA has erected at Sal Airport. Adjoining the equipment room is the operations room, with three dual controller positions and a supervisory position. On the equipment room's other side is a technical room housing a monitoring and control position. Uninterruptible power supplies, emergency generators, the air-conditioning plant and ancillary equipment are located in a separate support services area.

At the building's opposite end, next to the operations room, is a training area that includes simulation. Upstairs are offices and an area for meetings and presentations.

Much of the training required to qualify controllers for radar operation takes place at the area control center. AENA instructors first conduct a basic radar course on site. Trainees then go to Spain where they can use more comprehensive ATC simulators during an advanced course. Then they return to Sal for an on-site operational course that includes modules on airspace structure and new procedures. Final radar controller licensing follows further on-the-job training with tutorial assistance by AENA instructors.

Indra has installed a dozen AirCons in 10 countries in Central and South America, Africa and central Asia. Raytheon, similarly, has a global installation base with its AutoTrac system. Cape Verde, the two companies claim, affirms that their partnership brings both technical and marketing synergies to air traffic management.

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