Protecting Investment in an Air Traffic Management Legacy System
The modernisation of an Air Traffic Management system is another success story for Objektum Modernization. The initial contract to migrate the software from an obsolete to a modern platform is now complete with trials underway at Frankfurt airport under the auspices of THALES ATM. The system, known as the AP100 Watchkeeper, was originally developed in 1993 by THALES ATM formerly Siemens Plessey, for a DECAlpha platform. This platform is now obsolete and consequently problematic to resource. THALES ATM selected Objektum because of their unique mix of technical skills, to mitigate the risk posed by the platform obsolescence and form a partnership for the Through Life Support of the AP100.
AP100 Watchkeeper
The AP100 provides a single autonomous display, supporting up to two radar situation windows which present processed radar data to the operator from two independent radar data input streams. The system can handle up to 400 targets per scan and 100 targets per second. Radar data processing includes primary and secondary tracking data, automatic code/callsign conversion and assignment, emergency code, attitude indication, barometric pressure selection/correction and aircraft arrival/departure time detection. System interfaces allow remote pressure and radio direction finder values to be supplied and remote code/callsign assignment.
The extensive user interface provides facilities to pan / zoom, define the target label display, hook individual targets, define target trails and prediction vectors, display range rings, select up to 32 maps, display pixel maps, define height and code filters, perform recording / replay, define an area-of-interest (AoI) and produce hardcopies.
The AP100 can receive a single or two merged streams of pre-processed and validated radar data via either an X25 interface or recording file. It performs radar data processing, controls the windows graphical interface and situation display window, which contains the radar picture; including real-time plots, target labels, maps and other features selected by the operator.
The AP100 uses much of the functionality provided by DEC-Motif, which is a proprietary version of Motif®. The Motif® standard defines a graphical user interface (GUI) that provides application developers, end users, and system vendors with the industry's most widely used environment for standardising application presentation on a wide range of platforms. The AP100 uses the Motif® User Interface Language (UIL), some of which is DEC proprietary, to define the widgets, drop-downs, menus, etc that comprise the GUI. The Motif resource manager (Mrm) uses the X-Server Resource Database to define the generic look and feel of the application (borders, colours, etc), which is merged with site-specific and user adaptation resource files.
Product Migration
The software comprises approximately 122,000 lines of code, of which 75% is Ada83 and C application software (executing across 22 tasks); the remainder is Motif® and other support software.
A major risk to the project was that no vendor exists that can supply X25 interface hardware with an Ada API. Sangoma Technologies Inc. was selected to provide an intelligent multi-protocol WAN ADSL adapter, Linux kernel device drivers and a socket based API (written in C) which Objektum used to develop Ada95 bindings. This enables X25 radar data to be read by the application on a Linux platform.
The Radio Direction Finder (RDF), barometric pressure (QNH) and Mini ASCAP communicate with the AP100 via RS232. The V24pipe (RX/TX), written in C, simply routes data via named pipes to/from the RS232 devices. Using Ada95 LRM Annex B Interfaces, Ada bindings were developed to allow the application to read / write data via Linux named pipes.
The TECOS/ARRCOS interface employs Remote Procedure Calls (RPC) over TCP/IP to perform code/callsign assignment. Using Ada95 to C interfaces, Objektum developed a set of classes, implemented in Ada95, to allow Linux network sockets to be created and used to send and receive network data. These classes act as the conduit through which the RPC data is communicated.
Due to lack of test rig availability, limited integration time and the desire to minimise on site disruption, Objektum developed a comprehensive set of interface simulators using TCL, Visual Basic and C. This approach yielded a 50% reduction in on-site integration time and resulted in zero faults being reported.
User Interface
As can be seen in Figure 2, the AP100 uses a combination of Mrm, Xm, Xt and Xlib calls to create a GUI that allows radar tracks to be plotted efficiently on several screens superimposed on digital maps. The challenge for Objektum was to source or develop an Ada binding for OpenMotif (an open source code version of Motif®). Unfortunately, there are no publicly available Ada bindings for the latest version of OpenMotif. Moreover, there are backward compatibility and threading issues with this distribution. Hence, the Intermetrics Inc. X, X-Toolkit, X-Lib and Motif bindings were selected in conjunction with OpenMotif release 2.1.30-4. This proved to be an excellent choice and although all X/Motif interfaces had to be changed in the AP100 source code, a more structured approach, that exploits Ada95’s child packages and Interface annexes, was enforced by this binding.
Ada encourages good programming practices by incorporating software engineering principles with strong typing, modularity, reusability, readability and portability, which should reduce software development costs and significantly assist maintainability. The use of compiler/platform specific types and packages, maths libraries and other non portable language features in the original AP100 software reduced these benefits. It was Objektum’s aim to improve the portability and maintainability during the migration exercise by utilising new Ada95 language features, such as the numerics package, Object Oriented (OO) features, Command Line, Interfaces (C and C.Strings) and use type.
Extended Life
Numerous airports across Germany such as Frankfurt, Düsseldorf, Mönchengladbach, Paderborn, and Kiel currently employ the AP100 to monitor approaching and departing aircraft. By migrating the software to a modern platform, the original investment in the legacy system has been protected. Once the migration is complete, new features and enhancements become possible, further extending the life of the AP100 system.
Clients are already requesting functional enhancements such as new radar data formats, conformance monitoring for runway alignment, multi-radar tracking and squawk identification – none of which would have been possible on the legacy system.
Jürgen Kleinschmidt, Head of ATAS Service Centre at Thales ATM, Koblenz said “We are extremely pleased with the migrated product delivered by Objektum. Having the AP100 running on a modern Linux platform allows us to support our current customers, provide enhanced features and generate new business.” He added “Through our trusted partnership with Objektum we have protected our investment in the AP100 and given the airport operators an option for increased functionality.”