Temporary availability changes coded as a supplementary branch

Several AIXM features, such as AirportHeliport and the movement area elements (RunwayDirection, Taxiway, etc.) have associated "availability" objects that enable the coding of restrictions concerning the usage of the facility. This object typically has an operational status property which can take values such as 'NORMAL', 'LIMITED', 'CLOSED'. The same "availability" object is used for coding both baseline usage limitations and temporary situations. 

A temporary change (downgrade or upgrade) that affects the aerodrome movement area availability is usually notified without indicating that the usage limitations from the baseline data remain applicable. That is implied. For example, a TWY could have a baseline limitation related to aircraft wingspan - "not larger than 45 meters". If a NOTAM announces that that TWY is temporarily limited to "turboprop aircraft only", then this is interpreted as an additional restriction, not as a replacement of the baseline restriction. During the NOTAM effectivity, the TWY will be limited to both turboprop and maximum 45 m wingspan, even if the NOTAM text does not explicitly mention that the baseline limitation needs to be also considered. 

The same logic applies in case of a temporarily extended availability of a surface of facility. If a temporary extension of the aerodrome working hours is announced, then the NOTAM typically indicates these supplementary working hours, without repeating the baseline working hours.

In order to facilitate the coding and especially the NOTAM generation algorithm, the following approach is applied in the coding scenarios concerned (see also the diagram to the right):

  • it is assumed that the baseline situation is always coded using a 'NORMAL' operational status;
  • the TEMPDELTA Timeslice created with the Event will include
    • a branch that is identical to the 'NORMAL' status, copied from the BASELINE. 
    • an additional branch with status 'LIMITED' or 'OTHER:EXTENDED' / 'OTHER:UPGRADED' which is used for coding the additional limitations/extensions that apply during the event, as indicated in the diagram to the right.

AIXM 5.1(.1) Limitation

The current AIXM model misses the possibility to indicate 'extended" or 'upgraded' conditions. This possibility will be added in the next AIXM 5.2 version in the list of values used for Service availability and AirportHeliport elements. In the current model, the "OTHER:EXTENDED' or "OTHER:UPGRADED" codes will be used, as detailed in the corresponding coding scenarios.

The 'NORMAL' branch copy is necessary in order to comply with the AIXM Temporality Concept provisions for multi-occurring properties (version 1.1, item The availability properties included in the TEMPDELTA completely replace the availability properties from the BASELINE. Therefore, a copy of the BASELINE limitations is necessary in the TEMPDELTA, so that these limitations are not lost. 

The data user has to test the given flight/aircraft against both the 'NORMAL' and the additional branch:

  • if the additional branch has operationalStatus equal-to 'LIMITED', then failure to comply with either the NORMAL or the LIMITED branch is considered an infringement of the usage limitations.
  • if the additional branch has operationalStatus equal-to 'OTHER:EXTENDED' or 'OTHER:UPGRADED', then failure to comply with both the NORMAL and the EXTENDED/UPGRADED branches in the same time is considered an infringement of the usage limitations

Conceptual difference between .CLS and .LIM scenarios

A temporary closure of an aerodrome movement area or aircraft stand could come with some exceptions, such as "prior permission required (PPR)", "except locally based aircraft", etc. In these situations, the aircraft/flights that are still allowed to use the aerodrome element concerned need to comply with other availability restrictions that were specified as baseline data.

For example, if an aircraft stand is restricted in the baseline data for "wingspan not larger than 60 m" and that aircraft stand is "temporary closed except for home based aircraft", then the home based aircraft still need to comply with the 60 m wingspan restriction. Thus, this is not a real closure, it is just an additional availability condition ("only for home based aircraft") worded as a "closure with exception".

Therefore, all .CLS scenarios cannot allow exceptions. If any exceptions are specified, than the .LIM coding scenarios need to be used.

Similarly to the .LIM scenarios, the .CLS scenarios for aerodrome elements that have a baseline Availability are coded as a separate branch, as indicated in the diagram to the right. The Baseline availability is still copied in the TEMPDELTA, because these usage restrictions might still be applicable in case the closure is limited to a time schedule. The separation between the baseline data and the temporary closure data facilitates the automatic generation of the NOTAM messages.

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