Definición en inglés

The Flight Progress Monitor (FPM) is a research tool for ground-based conformance monitoring being developed as part of the Programme for Harmonised Air Traffic Management Research in Eurocontrol (PHARE) [Jansen et al. (1999)]. All of the PHARE tools are based on a 4D ATM philosophy, where an entire “tube” trajectory [Wilson (1996)] is verified to be conflict free during the planning phase, as illustrated in Figure 2.9. Once this trajectory has been accepted by an aircraft, it is assumed to agree to stay within its “contract tube” to ensure a conflict-free evolution of the flight.

Assigned trajectory “Contract tube” boundary

Note that the “tube” shown in Figure 2.9 is the 3-dimensional component of the contract swept out over time. The actual airspace contracted with the aircraft is considered to be a 4D “bubble” defining lateral, vertical and temporal (longitudinal) contract components. This is illustrated in Figure 2.10 for the horizontal dimension, along with the additional tube types that are defined inside and outside the contract tube for use by the FPM tool. Each type are discussed in more detail in the next section.

Large deviation tube Large deviation tube Contract tube Contract tube Error tube Error tube Assigned trajectory Predicted 4D position 4D contract bubble

Figure 2.10: PHARE Tube Definitions [Wilson (1996)]

Inside the contract tube resides an “error tube” which is used to account for the likely inaccuracies in the variables input into the forecasting process and the errors of the aircraft trying to follow the trajectory (i.e. the Flight Technical Error). Note that the errors may not be constant for a given trajectory (e.g. if the navigation system performance varies as a function of distance from a navigational aid). The contract tube is generated to be larger than or equal to the error tube in all dimensions so the aircraft should always have the navigational tracking capability to remain within it. The relative size of the tubes depend on the application: for example, at take-off and landing the contract tube and error tube may be coincident, while the contract tube is likely to be larger than the error tube in the en-route environment. Although the preliminary PHARE research studies used simple pre-determined contract tube dimensions of ±1 nm laterally, ±200 ft vertically and ±10 seconds longitudinally [Wilson (1996)], it is suggested that in an operational system the contract tube sizing could be linked to the known navigational capabilities of the aircraft or the RNP specification of the airspace.

Outside of the contract tube resides a “large deviation tube” which defines the boundary of recoverable navigation errors for the aircraft, i.e. a deviation from the 4D trajectory which is small enough to allow the aircraft to recover within the contract tube by the current sector boundary and which causes no hazard to other aircraft. This tube is used by the FPM to issue a large deviation alert when the aircraft flies outside of its boundaries, and the trajectory must be renegotiated. Again, the size differential between the large deviation tube and the contract tube is a function of the operational environment. They may be coincident at the runway, while the large deviation tube is likely to increase in size relative to the contract tube in the en-route domain, or decrease in relative size as traffic density increases such that only small deviations can be tolerated if conflict-free trajectories are to be maintained.

The FPM tool compares the tracked 4D aircraft positions with the predicted 4D position from the contract bubble and calculates the deviation and deviation trends (i.e. increasing, steady or decreasing) in the lateral, vertical and longitudinal directions [Jansen et al. (1998)]. The sizes of the deviations are then classified into three types [Jansen et al. (1999)]:

• “Insignificant”, meaning that the aircraft has almost no deviation (i.e. inside the “error tube”). • “Medium”, meaning that the aircraft is deviating (i.e. outside the “contract tube”) but is still able

to return to its planned trajectory. Careful monitoring is required.

• “Large”, meaning the aircraft has deviated outside the “large deviation tube” and is no longer able to return to the contracted 4D trajectory. A new contract trajectory needs to be negotiated and separation from other traffic is a high priority.

This conformance monitoring process can be classified as three signal-based fault detection schemes operating simultaneously. The signal is the same in each case (the deviation of the observed 4D position relative to the predicted 4D position) but this is compared to three different thresholds. Graphical display of the relevant aircraft deviation status is given to the controller via a display for subsequent planning, although no information on the display element of the tool was available.

There are several interesting elements of the FPM architecture from a conformance monitoring perspective. Firstly, the use of sets of nested tubes defining various thresholds and the use of a contract scenario are unique to this tool. Again the tube dimensions are considered to vary as functions of the scenario of interest (such as aircraft equipage), although interestingly there is no explicit suggestion of different thresholds being required during transitioning flight regimes. However, the FPM documentation [Jansen et al. (1999)] indicates that the biggest research challenge is in the determination of the

dimensions of the various tube types under various environments, for example subject to differing traffic densities and meteorological conditions.