Flight Restrictions (overview)

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Last updated: 2024 Jun 19

Introduction

AIXM 5 also contains a series of classes that model "flight restrictions". The initial objective was to enable the coding in AIXM of the Eurocontrol "Route Availability Document (RAD)" restrictions. At that time (around 2003), many of these restrictions also appeared in the AIP ENR 3.x tables.

Flight restrictions are in fact constraints that need to be checked on a flight plan or intended flight trajectory. They are expressed as a series of simple statements (such as departing from an airport, crossing an airspace, having a specific communication or navigation equipment, etc.) linked with logical expressions (and / or /..) and eventually an order in which the statements need to be considered.

AIXM flight restrictions overview

The flight restrictions model in AIXM 5.1 is presented below in a simplified form.

UML classes

As shown in the diagram below, a FlightRestriction in AIXM consists of one ore more routes (FlightRestrictionRoute) that are regulated by it (lower path) and a definition of a set of conditions (FlightConditionCombination) that a flight has to fulfill to be affected by the regulation (upper path). Moreover it is possible to define a flight level or flight level range inside of or at that the restriction applies.

The figure below shows the top-level AIXM 5 classes involved in the modelling of the flight restrictions concept:

A FlightRestriction is defined in AIXM as "a rule meant to regulate the use of the route network, by identifying a set of flights which fulfill a combination of elementary flow conditions and either forbidding them on a particular routing or obliging them to follow one routing out of a set of mandatory alternatives." The model is very flexible and it allows coding both very simple restrictions such as VFR flights not allowed at a particular airport or in a particular airspace and relatively complex restrictions, such as mandatory routes between city pairs.

The FlightRestriction class has an attribute (designator) that allows to identify the restriction using a human-readable coded identifier or name. The instruction attribute allows to provide a human-readable description of the restriction, explaining what flights and what routes, airspace, etc. elements are concerned and how.

The flights that are subject to the restriction are identified through the association appliesToFlight with the FlightConditionCombination class, which allows to specify a combination of elements such as departing from a specified airport, entering a specified airspace, using a specified type of aircraft, etc. This includes the possibility to define a schedule of applicability for the restriction, as the FlightConditionCombination is derived from PropertiesWithSchedule. The routes or other locations that are affected by the restriction are identified through the regulatesUseOf association with the FlightRestrictionRoute class.

The type attribute is used in combination with the appliesToFlight and regulatesUseOf associations and it may have the following values:

  • 'FORBID' - indicates that the flights that fulfill the conditions identified through the FlightConditionCombination are not allowed on the routes/trajectories identified by the associated FlightRestrictionRoute. If there are no specified FlightRestrictionRoute associated with the FlightRestriction, then the flights that fulfill the condition are simply not allowed at all;
  • 'MANDATORY' - indicates that the flights that fulfill the conditions identified through the FlightConditionCombination are obliged to use one of the routes/trajectories identified by the associated FlightRestrictionRoute;
  • 'ALLOWED' - indicates an exception, in the sense the indicates that the flights that fulfill the conditions identified through the FlightConditionCombination are explicitly allowed, in general or on the specific associated FlightRestrictionRoute, even if they might be not permitted by one or more other restriction. An explicit allowance overrules any other kind of restriction.
  • 'CLSD' - meaning specifically "closed for cruising", which indicates that the flights fulfilling the conditions identified through the FlightConditionCombination are not allowed to use in full the routes/trajectories identified by the associated FlightRestrictionRoute; It is allowed to climb or descend through the levels associated with the restriction but it is not allowed to fly straight and level on the said levels, in any part of the route.

Usage examples

The FlightRestriction feature and the associated classes are used in the Eurocontrol NM B2B service for providing in AIXM format the restrictions contained in the Route Availability Document (RAD).

In addition to this primary use, the FlightRestriction feature could theoretically be also used for indicating that a certain equipment is required for operating in an Airspace, at an AirportHeliport, on a Procedure, etc. as explained below: