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ARC - Advanced Research in Air Traffic Control - Linking TUB's Airbus A340/340 Full Flight Simulator to an ATM Simulator of Eurocontrol's Experimental Centre

Prof. Dr.-Ing. G. Hüttig
Wissenschaftliche Mitarbeiter
Dipl.-Ing. E. Brämer
Eurocontrol Experimental Centre (EEC)


In future Air Traffic Management (ATM) data link between aircraft and Air Traffic Control (ATC) will play a significant role. By linking an Airbus A340/A330 Full Flight Simulator (FFS) - located at TUB and operated by the Zentrum für Flugsimulation Berlin (ZFB) - to an ATM Simulator of Eurocontrol’s Experimental Centre in Brétigny/France, the project’s objective is to execute various experiments with focus on advanced air-ground data link scenarios using highly sophisticated and geographically dispersed devices in a distributed simulation environment.

For these trials, a simulation environment with very high en-route traffic scenarios is used. On the air side, the generic Flight Management System (FMS) of the Scientific Research Facility (SRF) as part of the A340/A330 FFS has been appropriately modified in order to establish the air-ground data link and the necessary negotiation process. Apart from simulation management data, such as start/resume, stop/freeze, clock synchronization etc., data to be exchanged between the two simulation facilities contain clearance requests, confirmations and refusals, flight plans, trajectories, constraint lists and position information.

They are transmitted via ISDN (Integrated Services Digital Network) using the Distributed Interactive Simulation (DIS) protocol. In order to cope with the special requirements for air-ground communication in civil Air Traffic Control (ATC), the above mentioned messages are transmitted using standard DIS protocol data units (PDU). It is further foreseen to integrate additional ATC and flight simulators in a distributed simulation scenario thus allowing to take full advantage of various technical infrastructures provided at different sites.

The simulation of a data exchange between aircraft and ground stations takes a major part in the overall ATM system validation process. This document will highlight the associated research activities performed at TUB to link an A340/A330 FFS to Eurocontrol’s ATM research testbed. In this context, the following chapters will describe the distributed simulation and communication environment, the planned simulation scenario, the developed data link module software as well as the already performed data exchange trials using the DIS protocol library.

Presentation of the Distributed Simulation Environment
The "airborne" and "ground" site play the following role in the simulation process:

ZFB’s Scientific Research Facility

The A340/A330 FFS is extended with a so-called SRF, which consists of an IBM workstation identical to and independent of the simulator host computer with additional scientific research features for display development, testing of experimental hard- and software avionic units or audio and video recording. An ISDN router is responsible for the communication with external computer systems.

Eurocontrol’s ATM Network

Eurocontrol’s system environment consists of several workstations which provide all necessary functions to develop and apply the appropriate ATM software. Again, an ISDN router is responsible for the communication with external computer systems.

Linking the Two Simulation Facilities

ISDN is used as data link medium between the two simulation facilities. In comparison to other transmission media such as Internet, ISDN provides, due to its duplex transmission technique, reliable data exchange rates. This is very important to allow for realistic transmission modeling. As protocol, DIS has been chosen because it provides all the required functionalities and minimizes the network bandwidth use. In addition to the automatic data exchange via DIS, a voice link is also provided by a telephone installed in the cockpit of the A340/A330 FFS. This may be of importance for the exchange of supervisor information during the distributed tests as well as for the simulation of a back-up voice link between pilot and controller in case of communication system failures.

Defining the Simulation Scenario
The main purpose of the A340/A330 FMS is to reduce pilot workload and fuel consumption by guiding the aircraft as accurately as possible along an optimized flight trajectory, depending upon actual environmental and performance criteria and taking into account ATC requirements. On the other hand, the objective of Eurocontrol’s ATM simulator is to investigate the feasibility and operational value of enhanced air-ground integration and coordination. Ground station and aircraft are assumed to communicate via data link, only. In order to combine the two system philosophies and to provide the necessary flight management and guidance functionality, the definition of a suitable simulation scenario is therefore very important.

Trajectory Negotiation Process

The trajectory negotiation process follows the recommendations of FANSTIC II [1]: The negotiation process may be initiated by the airborne or ground side respectively. The pilot requests for ATC clearance by downlinking an intended trajectory. ATC evaluates the requested trajectory and sends either a constraint list - which may contain several lateral, vertical and time revisions related to each flight phase - or an approval. The approved trajectory is activated and executed by the pilot. In case either the aircraft or ATC is no longer able to comply with the contract, the trajectory has to be re-negotiated.

Data to Be Exchanged

From the selection of available DIS PDUs, the following are used within the simulation (refer to [2] for a detailed description of the particular PDU fields):

  • Entity State PDU: The entity state PDU shall communicate information about a particular entity to represent the issuing entity in the receiving simulations like entity identification, entity location and velocity.
  • Start / Resume PDU: This PDU indicates, that a particular entity is to leave a stopped or frozen state and begin participating in a simulation exercise at a certain time.
  • Stop / Freeze PDU: This PDU is used to stop or freeze an entity or exercise. It has to be sent early enough to allow the receiving entity to comply.
  • Data Query PDU: A request for data from an entity is communicated by issuing a data query PDU.
  • Data PDU: The data PDU is used in response to a data query PDU. It allows the entity to provide the requested information.
  • Signal PDU: The signal PDU may be used to convey audio or digital data carried by the simulated radio transmission.
  • Transmitter PDU: This PDU finally contains information about the state of a particular radio transmitter like identification, frequency etc..

The data actually to be exchanged explicitly contain:

  • Simulation management information:

    • clock synchronization
    • start / resume simulation
    • stop / freeze simulation

  • ATC requests:

    • call sign, transponder code and optionally: country ID and category ID (data query PDU)

  • Information about the A340/A330:

    • position and dead reckoning (entity state PDU)
    • call sign, transponder code and optional: country ID and category ID (data PDU)

  • Trajectory information:

    • trajectory with origin, destination, waypoint type and name, position, altitude, estimated time of arrival, radius of turn (signal PDU)
    • trajectory activation (signal PDU)

  • Constraint lists:

    • constraint list with origin, destination, constraint point type and name, latitude, longitude, lateral attributes (requested - upper margin - lower margin), altitude attributes, speed attributes and time attributes (signal PDU)
    • constraint list activation (signal PDU)

  • Information About Other Aircraft:

    • the Data Link Module can display surrounding air traffic by processing entity state PDUs and data PDUs

Adaptation of the A340/A330 Flight Management System

Structure of the Data Module

Multiple software modifications were necessary to establish the link.

Procedure to Extract the Necessary Aircraft Data

In modern flight simulator software, aircraft parameter are handled in a Common Data Base (CDB). All communication between the software modules is routed through the CDB. To not disturb the timely sensitive simulation process a procedure has been developed to allow access of the data link module via a commonly shared memory area.

Airborne Data Link Module

The data link module is responsible for receiving ground initiated requests transmitting all necessary aircraft data (like position, trajectory etc.) and simulation management data to the ground station via ISDN, based on the DIS protocol. Its structure is represented in figure 1.

The main program loop containing the message handler checks for incoming messages (PDUs) and links the appropriate procedures responsible for processing. The following functionalities are performed by the airborne data link module:

  • System and network initialization
  • Aircraft state and dead reckoning calculation and transmission
  • Processing of incoming messages (start/resume, stop/freeze, create/remove entity, data queries, constraint lists)
  • Extraction and transmission of FMS computed trajectories
  • FMS input, presentation and checking of constraint lists

The module consists of C programming code. It is supplemented with C++ functions provided by Eurocontrol for the encoding of trajectories and decoding of constraint lists respectively. Corresponding to FANSTIC II, the data link message contents are derived from files written in ASN1 (Abstract Syntax Notation One) format which are converted into C++ code for further linking. Distinguished Encoding Rules (DER) are used to encode the data into a binary stream.

Human Machine Interface

It is well obvious, that the discussed realization of external FMS data input requires an adequate human machine interface (HMI) for the pilot. In connection with the SRF at TUB, the aircraft Navigation Display (ND) and the MCDU (Multipurpose Control and Display Unit) have been appropriately modified for this purpose. The developed functionalities for short terms compose:

  • Information of the pilot about the reception of a constraint list, clearance etc. on ND and MCDU
  • Online-information of the FMS data insertion process (e.g. transmission of a constraint list)
  • Acceptance of pilot inputs like „send trajectory", „copy constraint list" or „send trajectory activation" via MCDU push-buttons.

Display of Surrounding Air Traffic
As already mentioned, the Data Link Module processes information about surrounding air traffic. It filters out interfering aircraft and displays them together with their altitude and call sign on the pilot's Navigation Display (ND). DIS Air-Ground-Air Communication Trials After establishing the physical link between the two simulation facilities via ISDN and completion of FMS software modifications, current work now concentrates on several simplex (air-ground) and duplex (air-ground-air) trials to validate and verify the reliability of the overall integrated ATM system.

Integration of a Dialog Test Facility

In order to test the data transmission from and to the aircraft simulator, a Dialog Test Facility (DialTFac[i]) representing a simplified ATC ground simulator, was used. Its main objective is to provide an interface to display aircraft traffic and to enable trajectory negotiation with multiple aircraft simulators using the DIS protocol.

Initial Simplex Testing

A simplex test proved the system’s reliability in a distributed simulation environment [3]:

  • A complete flight between Amsterdam and Paris Charles-De-Gaulle was executed.
  • The A340/A330 FFS, the DialTFac and an utility to log the network traffic were connected using the DIS protocol.
  • The exercise contained a start at a given simulation time, arbitrarily freezes and resumes and a total freeze (stop) at the end of the session. During execution, several flight plan modifications were introduced by the pilot and sent to the DialTFac where they were displayed on the control screen.

The test was successfully completed at TUB. The examination of the number of PDU’s which have been transmitted during flight proved the suitability of even simple DIS dead reckoning algorithms to reduce network traffic.

Duplex Trials

The initial simplex working version of the DialTFac which allowed the reception and presentation of trajectories and other aircraft related information like position, orientation, transponder code and call sign was replaced by a duplex version at the beginning of project phase 2 which additionally allows the creation and transmission of constraint lists.

Initial stand alone and distributed tests with this duplex version have been successfully completed at TUB in September 1996. Further trials now concentrate on data communication with Eurocontrol via ISDN. An additionally implemented voice link which is also controlled by the DIS protocol library (event report PDU, receiver PDU, transmitter PDU) allows the exchange of supervisor information as well as the pilot-controller communication in the case of a not fully automatic working ATC ground station. This will finally conclude the tasks which had to be performed during the project. A possible project extension could lead to a common participation in PHARE 3 (Program for Harmonized ATM Research in Eurocontrol) demonstration.

This work is wholly funded by the EUROCONTROL Experimental Centre under Contract C/1.100/CE/BE/95. The EEC Technical Monitors Christian Pusch and Eric Hoffman. The DIS protocol library and the DialTFac were developed at the EEC and provided to TUB.


  1. CENA, FANSTIC II Report, 1994
  2. Standard for Distributed Interactive Simulation- Application Protocols; Version 2.0, Fourth Draft; University of Central Florida; February 4, 1996
  3. E. Brämer, Intermediate Report Project Phase 1 - July 1995-May 1996, Berlin , June 5, 1996


G. Hüttig, H.Fricke, E. Brämer [1996]: "Distributed Simulation For Advanced Research in Air Traffic Management - Linking an A340/A330 Full Flight Simulator to an ATM Simulator of Eurocontrols Experimental Centre"; Proceedings of the Conference - "The Progress and Direction on Distributed Interactive Simulations" - 6/7 November 1996, London, Great Britain.

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