Graham Warwick/ATLANTA
INCREASES IN airspace capacity promised by new air-traffic-management technologies such as Free Flight will challenge airports' ability to cope unless control of aircraft on the ground is similarly improved.
The US Federal Aviation Administration is already tackling the problem on the ground, developing systems to display runway status, to tag surface-movement-radar returns with aircraft identity and to advise the ground controller on runway use. NASA, meanwhile, is looking beyond the year 2000 at aircraft systems which could increase airport capacity.
The Terminal Area Productivity (TAP) project is a wide-ranging effort under NASA's Advanced Subsonic Transport programme to develop technology for next-generation airliners. The TAP goals include the automation of terminal-area air-traffic-management; the reduction of spacing between aircraft on final approach; and the faster movement of aircraft off the runway and to the terminal.
Clear the runway
The latter aim falls under the Low Visibility Landing and Surface Operations (LVLASO) programme. According to NASA, the goal of this project is to improve the efficiency of airport operations in Category IIIb low-visibility conditions, demonstrating at least a 12-15% increase in runway throughput.
LVLASO programme manager at NASA Langley Wayne Bryant says that the project has three elements: a roll-out and turn-off (ROTO) system to provide braking commands to the crew to reduce runway-occupancy times; a taxi-navigation and situational-awareness (T-NASA) system to provide the crew with airport maps, taxi guidance and collision warning; and a dynamic runway-occupancy measurement (DROM) system, to determine the spacing between landing-aircraft pairs.
A demonstration is planned for May 1997 at Atlanta's Hartsfield International Airport, in Georgia, using NASA's Boeing 757 testbed, with additional, increasingly integrated, demonstrations planned for 1999, probably at Dallas/Fort Worth, and the year 2000. Development of the ROTO system will be in two phases. Initially, the system will provide information to the pilot on "braking strategies" to reduce runway occupancy. This will be in the form of advisory commands, but cost-benefit studies are under way into the next phase, an automated braking-control system which would guide the aircraft to a specified runway exit.
The ROTO system is designed to reduce average runway occupancy by 20%, and reduce the variability of runway-occupancy time by 30%, making it easier to predict how long a specific aircraft type will spend on the runway, Bryant explains. McDonnell Douglas is developing the software, using differential global-positioning-system navigation to provide precise location of the aircraft on the runway.
Three elements make up the T-NASA system - a moving-map display of the airport showing the taxi route and other traffic; head-up display (HUD) symbology showing runway edges, guidance cues and traffic information; and a three-dimensional audio system providing a directional warning of a ground collision.
Jeppesen Sanderson is developing the electronic airport-database, which will be used to generate the moving map. Taxi-routing and traffic information will be uplinked to the aircraft via VHF datalink, displayed on the map and HUD and used to generate collision warnings.
The third element of the LVLASO programme, the DROM system, will reside in the control tower. The system is closely allied to another element of the TAP programme, the aircraft-vortex spacing system (AVOSS), Bryant says. Aircraft separation on final approach is determined primarily by the need to allow the preceding aircraft's wake vortices to dissipate. Approach spacing is now based on the relative sizes of the aircraft in a landing pair, with more separation required if a small aircraft follows a heavy aircraft. The AVOSS programme is developing means to measure the strength and persistence of wake vortices in real time, and use this to advise the controller on separations.
About 30% of the time - when a heavy aircraft follows a small aircraft, Bryant explains - approach spacing is determined by runway occupancy. The DROM system will measure runway occupancy continuously and will provide the AVOSS with an average time each aircraft type is expected to remain on the runway in the weather conditions prevailing. This will be used to advise the controller on spacing.
Seeking standards
The DROM system uses Cardion's co-operative aircraft tracking system (CAPTS) to determine aircraft identity (and type) and position. The CAPTS listens passively to aircraft Mode S transponder replies and uses a technique known as multi-lateration, to locate the aircraft.
NASA's LVLASO programme will result in standards for an aircraft surface-operations system. Bryant says that the USA has been tasked by the All-Weather Operations Procedures panel of the International Civil Aviation Organisation to define the required routing performance for an advanced surface-movement guidance and control system (ASMGCS). This is the ground equivalent of required navigation performance (RNP), he explains.
RNP defines the aircraft-positioning accuracy required for each phase of flight, and so determines how an aircraft should be equipped. Required routing performance will do the same for surface operations, Bryant says, and the LVLASO demonstrations will generate much of the data required to validate the ASMGCS standard, expected to be issue later this decade.
Source: Flight International
