Relaxing the maximum limit of certain features in a report which are mandatory requirements in Annex 3

[blchoy]

Patrick Simon gave the following comment on IWXXM 3.0.0RC3:

Hi

As already indicated, I am sorry not to be able to attend the meeting (ICAO EUR METG meeting at the same dates).

I have a question on IWXXM3.0.0RC3 , as I see that for RVR, there is a maximum limit of 4 ( both in the schema and schematron), and I thought we said that we will release these limits, as in certain cases, the aeronautical MET services on airport don't know the QFU in service (this is our case - Météo-France) and it is an information to be used not at the airport (therefore the QFU may change in between, not the case for local/immediate use information - but not provided in IWXXM yet) and some airports may have more than 4 runways ?

Kind regards,

patrick

@jkorosi pointed out there are similar restrictions need considering:

Hello all,

I think that all such restrictions should be considered:

• number of present weather phenomenon in METAR, SPECI, TAF (3)
• number of recent weather phenomenon in METAR, SPECI (3)
• number of cloud layer for TAF, METAR, SPECI (4)
• rvr for METAR SPECI (4)
• trend forecast in METAR, SPECI (3)
• number of temperature groups in TAF (2)
• the number of VA clouds in VA SIGMET (2)
• the number of TC centres of tropical cyclones in TC SIGMET (2)

I am not sure if the only driver for these restrictions was to minimize the report length or there are also other reasons. My point of view is that at least the number of VA Clouds and TC centers in SIGMET should be relaxed too.

Best regards, Jan

While most of us considered that the main reason for the restrictions is to limit the size of the TAC messages, in my limited understanding ICAO had also mentioned cost (i.e. cost to transmit longer bulletins, and even the cost for preparing bulletins with more content) as a factor.

I think the issue here is that even though we lifted the restrictions, the existing mandatory requirements in Annex 3 are still there and we still need to prepare Annex 3 compliant reports. Furthermore, if you allow people to report more in IWXXM only, then there will be incompatibilities with their TAC counterparts and this is also not desirable during the parallel run period.

My personal suggestion is to remove these restrictions from the schema and rely on the report creators to adhere to the Annex 3 requirements but not the validator. At the same time, we may want to bring to the attention of WG-MIE/6 and METP/5 the need to lift the restrictions from Annex 3 to support future requirements.

Happy to discuss.

[blchoy]

I took the liberty to include this as part of the work for Version 3.1.0 but need to get a green light from ICAO before actual implementation.

[blchoy]

A paper on Relaxation of TAC Constraints in IWXXM was discussed at WG-MIE/7. While the meeting supported the general concept of increased information within IWXXM, the group was concerned whether such changes were within the governance of WG-MIE, and particularly given WG-MRI was progressing use cases and user requirements for related capabilities. There were also concerns raised that some changes could negatively impact some users.

An ad hoc team was formed to review the proposal and agreed to support changes to three parameters, these being the removal of any limitation on the number of RVR values reported and an increase in the resolution of temperature & dew-point temperature values in METAR/SPECI, from one degree to tenths of a degree.

The above will be raised for METP/5 consideration, and subsequent approval by ANC/Congress through amendments to Annex 3.

This issue has completed its mission and is hereby closed.