AMOSSG/4-SN No. 12

21/8/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	5:	Aerodrome observation requirements
5.1:	Reporting requirements and criteria

HARMONIZATION BETWEEN WMO AND ICAO REGULATIONS, WITH RESPECT TO THE FM 15 METAR AND FM 16 SPECI CODE, REGARING THE ENCODING OF RUNWAY VISUAL RANGE

(Presented by Dennis Hart)

SUMMARY
The encoding practices for Runway Visual Range (RVR), based on WMO and ICAO regulations, show differences in the reporting of RVR; especially in the reporting scale. This study note suggests a possible solution.

1.	INTRODUCTION

1.1	The encoding of the FM15 METAR and FM16 SPECI is described in the WMO No 306 Manual on Codes and in the ICAO Annex 3.

1.2	In the METAR/SPECI code form the Runway Visual Range (RVR) information is reported using a strictly defined reporting scale.

1.3	When the regulations for the encoding of the RVR will be considered, it shows up that differences exist in the defined reporting scale when RVR values less than 800 metres will be encoded.

2.	DISCUSSION

2.1	According to the WMO No 306 Manual on Codes, the RVR should be encoded in the format VRVRVRVR. Exact specifications for this group are not available in the Manual except for the description of the symbolic letters VRVRVRVR. The reporting scale described for the RVR is in flexible steps of 25 to 60 metres up to RVR values of 800 metres and steps of 100 metres when RVR values are above 800 metres (see Appendix).

2.2	The encoding practice in ICAO Annex 3 however, is unambiguous in describing the reporting scale for RVR. The reporting scale consists of the increments in steps of 25 metres below 400 metres, 50 metres between 400 and 800 metres and 100 metres above 800 metres (see Appendix).

2.3	The encoding practices for RVR throughout the States are not unambiguous as a consequence of the differences in the WMO and ICAO regulations.

3.	CONCLUSION

3.1	A uniform reporting scale will be a benefit for e.g. LVP and other operations. Therefore it is proposed to harmonize both the WMO No 306 Manual on Codes and ICAO Annex 3 regulations on the subject of the RVR reporting scale. The current reporting scale described in ICAO Annex 3 will preferably meet the operational needs in the best way.

4.	ACTION BY THE GROUP

4.1	The group is invited to:

a)	note the content of this paper;

b)	agree on the proposal stated in paragraph 3.1, and

c)	undertake any further action , if necessary.

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