The ICAO Annex 15 recommends that “Global communication networks and Web services should, whenever practicable, be employed for the provision of Aeronautical Information Products.” The ultimate goal is to provide aeronautical data through Web services. The provision of the data sets (as files) is considered as an intermediate step in that direction. The rules provided in this section ensure a minimal harmonisation of the provision of Obstacle Data sets as files.

File structure

Although there are no specified rules, based on the current practices it may be assumed that State AIS are likely to publish:

a single 'Area 1 Obstacles' file for each contiguous State territory (mainland or remote territories);
a separate 'Area 2/3/4 Obstacles' file for each aerodrome/heliport;

However, deviations from this general rule are expected to occur in the following situations:

if a country has a very large territory and it's worth splitting the Area 1 per State, Region, etc.;
if two or more airports are closely located and their Area 2 data collection surfaces intersect, it is possible that a joint file is published for the Area 2. In this case, obstacles, if any, in area 3/4 might be included in the same file.

Important Note

Providing separate files for each Airport Area (2/3/4) might result in a significant number of VerticalStructure features appearing in several files. Identifying duplicates would require additional effort on the data users side. This might also result in smaller files that are updated at different dates. Identifying all the files that have changed and downloading a large number of files would also require additional effort on the data user side. Therefore, it is recommended that a single obstacle data set is provided for each airport/heliport, including all the VerticalStructure and their associations with the concerned ObstacleArea. If several files are provided, the possibility to download all at once should be provided, for example, as a zip archive.

File name

The ICAO PANS-AIM, item 5.4.1.4 requires a “checklist of data sets shall be made available through the same distribution mechanism as used for the data sets”. This implies that each data set may be uniquely identified by its name, so that it can be listed. Therefore, a naming convention for the Obstacle Data Set files is proposed in this section.

Recommendation

An Obstacle Data Set file should have the following name structure “CC_CC_CC…[_Territory_][CCAD_CCAD_...][ADName_ADName_...]_[RWYnnL]_OBS_DS_[AREA]_Variant_YYYYMMDD.xml", where:

CC represents the 1-letter or 2-letters ICAO Country code(s) of the State(s) under which authority the data set is published, according to the ICAO DOC 7910 - Location Indicator;
Note: When a Data Set is published for an entire region, as result of a regional database agreement, CC may be replaced by a code representing that region, such as “EU” in the case of the European AIS Database.
[_Territory] is optional and is the official name of the Territory covered by the data set, if applicable;
[CCAD] represents the ICAO Location Indicator of the aerodrome/heliport for which the data set is published. This cannot be used for data sets that contain only Area 1 data. It is mandatory for data sets that contain Area 2/3/4 data. If there is no ICAO Location Indicator, then "XX" or "XXX" (similar to the rules for the NOTAM Item A) should be used after the letter(s) that correspond to the State.
ADName represents the name of the aerodrome/heliport for which the data set is published, in case no ICAO Location Indicator is specified for the aerodrome/heliport. This cannot be used for data sets that contain only Area 1 data. It is mandatory for data sets that contain Area 2/3/4 data;
OBS_DS is a fixed text (meaning “Obstacle Data Set”);
[AREA] is an optional element and it indicates for which areas the data is provided in the file. It may take one of the following values if the data belongs to a particular area:
- AREA1 - for Area 1 obstacle data sets
- AREA[2][a][b][c][d][3][4] - for obstacle data sets that include one or more of the areas 2(a/b/c/d), 3 and/or 4
- AREA_MULTI - for other combinations of obstacle areas
Variant is a mandatory element and it can take one of the following values (based on the Data set variants guidelines):
1. FULL - when the file contains a complete Obstacle data set;
2. DIFF_BL - when the the file contains an Obstacle Data Set Differences variant coded with BASELINE TimeSlices;
3. DIFF_DELTA - when the file contains an Obstacles Data Set Differences variant coded with PERMDELTA TimeSlices.
4. SUP - when the file contains a Supplementary Obstacle Data set.

YYYYMMDD is the start of effective date in the format year, month, date;

For example:

“EK_OBS_DS_AREA1_FULL_20181123.xml” - the Area 1 Obstacle Data Set for the mainland Denmark effective on 23 NOV 2018;

“EK_Greenland_BGGH_OBS_DS_AREA2_FULL_20181123.xml” - the Area 2 Obstacle Data Set for the Godthaab / Nuuk Airport, in Greenland

“EB_EL_OBS_DS_AREA1_FULL_20181123.xml” - for the Area 1 Obstacle Data Set of Belgium and Luxembourg

Relation with metadata

It may be observed that most of the elements that enter in the composition of the file name are also provided as metadata. The purpose of the file name is to enable a quick identification of the data sets of interest. However, the data users should not rely only on the file name in order to decide on the suitability of processing/using a data set instance. The complete metadata should be used for this purpose.

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