AMOSSG/5-SN No. 20

23/3/05

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FIFTH MEETING

Montreal, 11 to 14 April 2005

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

CONSIDERATIONS FOR AUTOMATED REPORTS

(Presented by D. Hart and M. Leroy)

SUMMARY
The implementation by the Netherlands and France of amendment 73 of Annex 3 showed the interest and/or need of some clarifications for automatic observing systems. Proposals for such clarification are made, which could be part of amendment 74.

1.	INTRODUCTION

1.1	The introduction of fully automatic observing systems during non operational hours for Dutch and French Regional Airports introduced some procedural and coding difficulties to tackle. Difficulties on how to identify the absence of weather or cloud information in a report and to overcome unambiguous standards and recommendations from a programmers point of view.

1.2	These issues were never a real problem in the past, having man to support and augment the partial automated observations that were used. But they became evident when introducing new KNMI observing systems two years ago and changing them accordingly with standards and recommendations provided by the 15th edition of Annex 3. Some of the issues raised, need a global approach to prevent divergence in implementing rules for fully automated systems.

2.	DISCUSSION

2.1	Absence of information in automated reports

2.1.1	Providers of aeronautical observations should always have contingency procedures available to prevent sensors or other parts of the automatic observing system to fail. But in the unlikely circumstance of a failure, procedures should be in place to properly report such a situation. Not only in a NOTAM, if appropriate, but also in the report itself.

2.1.2	The current reporting practice for METAR and SPECI does not always clearly specify how absent observational information, caused by system failure, should be incorporated in associated reports. Currently, the absence of information in reports is an indication of a condition were it was not possible to observe a parameter, instead of an indication of (partial) system failure; in line with WMO No. 306: "when an element or phenomenon does not occur, the corresponding group, or the extension of a group, is omitted from a particular report".

2.1.3	A provision to indicate that it's not possible to report a required element of the automated report was introduced in the latest version of WMO No.306 (August 2001). "If any element cannot be observed, the group in which it would have been encoded shall be replaced by the appropriate number of solidi. The number of solidi depends on the number of symbolic letters for the specific group which is not able to be reported; i.e. four for visibility group, two for the present weather group and three or six for the cloud group, as appropriate".

2.1.4	Unfortunately, this guideline can still lead up to misunderstanding. For instance, one could argue that it is still unclear how to handle the cloud elements when there is a system failure for cloud information. Should a system report three, six or even nine solidi, if you also take in to account the requirement to report 3 solidi if it is not possible to observe the cloud type (Annex 3, Appendix 3, Paragraph 4.9.1.4)? This example points out another issue to consider.

2.1.5	The requirement listed in Annex 3, Appendix 3, Paragraph 4.9.1.4 is a the third type of reporting practice in relation with missing information. How to report the fact that an automatic observing system is not capable to report required elements from a technical perspective.

2.1.6	In conclusion, it could be stated that clear reporting practices for automatic observing systems should be in place to report when:

—	an element or phenomenon does not occur.

—	an element or phenomenon can not be reported because the system is technically not capable.

—	an element or phenomenon can not be reported because there is a (partial) system failure.

Furthermore, it can be concluded that only two options are available to report on of the three above mentioned:

—	omit a group or extension of the group.

—	replace the group or extension of the group by solidi.

Current requirements in Annex 3, as in the supportive WMO No.306, only partially give clear guidelines how to report what in a given circumstance. A reason for misunderstanding and misinterpretation in producing and using aeronautical meteorological reports.

2.1.7	It is therefore proposed to have clear requirements in the appropriate documentation to provide for an unambiguous reporting practice when an element or phenomenon does not occur and an element or phenomenon can not be reported because the system is technically not capable or in the case of a (partial) system failure.

2.1.8	Due to the current limitation of having only two types of identification for three types of information a pragmatic approach is suggested. From a users perspective it is more clear to have a distinction between non occurring elements and phenomena and the absence of information due to technical issues, i.e. failure or not capable to report then every other grouping of occurrences. The introduction of a third reporting practice, besides "omit" or "replace by solidi" is assessed as currently not feasible. Appendix A presents a proposed reporting scheme. Derived from this scheme, the appropriate requirements and practises in Annex 3 and WMO No. 306 could be changed. For clarity, the reporting practice for groups of the report that can be easily derived from the existing regulation are also listed in the table.

2.2	Reporting of NSC, SKC, NCD and CAVOK

2.2.1	With the introduction of edition 15 of ICAO Annex 3 new requirements for the reporting of clouds for automatic observing systems were introduced. Appendix 3, Paragraph 4.9.1.4 introduces the requirement to report "///" when the cloud type cannot be observed. NCD should be reported when no clouds are detected. Both requirements have impact on other requirements for reporting clouds throughout the appropriate parts of the Annex. Some additional guidance is probably needed and could be included in the relevant parts of Annex 3 for clarity.

2.2.2	When no clouds are detected by an automatic observing system, NCD should be reported. From current requirements it is not clear if NCD will substitute SKC in automated reports; from a technical perspective there is one observation with two possible outcomes. For automated reports it is proposed to clearly state the requirements to report NCD when no clouds are detected and consequently SKC should not be reported by an automatic observing system.

2.2.3	When the cloud type cannot not be observed by an automatic system, information on the cloud type needed for the determination of CAVOK and NSC is not available. It is proposed to add in the relevant paragraphs of Annex 3 a note in line with "when Appendix 3, Paragraph 4.9.1.4.a. is applicable, the abbreviations CAVOK and NSC shall not be used".

2.2.4	If an automatic observing system has the capability of reporting cloud type and there are no cloud detected, the absence of CB should be combined with NCD information; in this case only, NSC should be used and consequently CAVOK could be reported.

3.	ACTION BY THE GROUP

3.1	The AMOSSG is invited to:

a)	note the content of this paper;

b)	agree on the proposal stated in paragraph 2.1.8 and Appendix A;

c)	agree on the proposal stated in paragraph 2.1.9;

d)	agree on the proposal stated in paragraph 2.2.2;

e)	agree on the proposal stated in paragraph 2.2.3;

f)	agree on the proposal stated in paragraph 2.2.4; and

g)	undertake any further action, if necessary.

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AMOSSG/5-SN No. 20

Appendix

APPENDIX

A. Group	B. Reporting Practice*	C. Occurrence	D. Remark
A.1) Wind	B.1.1) ///12KT- KMH	C.1.1) Wind direction information is not available	-
B.1.2) 230//KT - KMH	C.1.2) Wind speed information is not available	-
B.1.3). /////KT - KMH	C.1.3) Wind direction and wind speed is not available

-
A.2) Visibility	B.2) ////	C.2) Visibility information is not available	D.2) 1 group of 4 solidi will replace all possible visibility groups.
A.3) RVR	B.3.1) R////////	C.3.1) RVR information not available	D.3.1) 1 group of 8 solidi, with the leading 'R" will replace all possible RVR groups.
B.3.2) R13/////	C.3.2) RVR information not available for the given touchdown zone	D.3.2) 1 group of 5 solidi preceded by the leading 'R' and location indication (RDrDr). To be used when at least one another RVR valid value is available for a touchdown zone (in such a case, R//////// cannot be used).

A.4) Present weather	B.4.1)<blank>	C.4.1) Present weather not occurred	-
B.4.2) //	C.4.2) Present weather information not available	D.4.2) 1 group of 2 solidi will replace all possible present weather groups.

A.5) Clouds	B.5.1) /////////	C.5.1) Cloud amount, height and type information is not available	D.5.1) 1 group of 9 solidi will replace all possible cloud groups.
B.5.2) BKN020///	C.5.2) Cloud type is not available for the given cloud layer.	D.5.2) 1 group of 3 solidi will replace cloud type. If the system is capable of detecting cloud type, but not to associate this type to a given cloud layer, several cases are possible : 1)If the system has not detected CB or TCU, cloud type is nevertheless considered as available for all cloud layers (the group of 3 solidi is not added, as information about the absence of CB and TCU is available), 2)If the system has detected CB or TCU, an additional cloud group (//////CB or //////TCU) is included (B.5.3).
B.5.3) //////
(//////CB)	C.5.3) Cloud amount and height information is not available, system is capable of detecting cloud type	D.5.3) 1 group of 6 solidi will replace all possible cloud groups, when appropriate directly followed by a cloud type.
B.5.4) BKN//////	C.5.4) Cloud height and type information is not available for the given cloud amount.	D.5.4) Cloud height information is replaced by 3 solidi in the appropriate cloud groups.
B.5.5) BKN/// (BKN///CB)	C.5.5) Cloud height information is not available, system is capable of detecting cloud type for the given cloud amount.	D.5.5) Cloud height information is replaced by 3 solidi in the appropriate cloud groups.
B.5.6) ///020///	C.5.6) Cloud amount and type information is not available for the given cloud height.	D.5.6) Cloud amount information and cloud type information are each replaced by 3 solidi in the appropriate cloud groups.
B. 5.7) ///020 (///020CB)	C.5.7) Cloud amount information is not available, system is capable of detecting cloud type for the given cloud height.	D.5.7) Cloud amount information is replaced by 3 solidi in the appropriate cloud groups.
B.5.8) NCD	C.5.8.) No clouds detected and the system is not able to report cloud type.	-
B.5.9) NSC	C.5.9) No clouds detected and no CB detected.	D.5.9) The system is capable of detecting cloud type and has not detected CB.

A.6) Air temperature and dew-point temperature	B.6.1) /////	C.6.1) Air temperature and dew-point temperature information is not available.	-
B.6.2) 14///	C.6.2) Dew-point temperature information is not available.	D.6.2) Dew-point temperature information is replaced by 2 solidi.

B.6.3) ///12	C.6.3) Air temperature information is not available.

D.6.3) Air temperature information is replaced by 2 solidi
A.7) Atmospheric pressure	B.7) Q////	C.7) QNH information not available.	D.7) 4 solidi, with the leading 'Q" will replace the QNH groups.

A.8) Recent weather	B.8) RE//	C.8) Information on recent weather phenomena is not available.	D.8) 1 group of 2 solidi, with the leading 'RE" will replace all possible recent weather groups.

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