AMOSSG/3-SN No. 7

2/1/02

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

THIRD MEETING

Miami, 22 to 25 January 2002

Agenda Item	5:	Review of the requirements for meteorological observations and reports at aerodromes contained in Chapter 4 of Annex 3

REVIEW OF THE PROPOSED AMENDMENT 73

(Presented by Wil van Dijk )

SUMMARY
This study note reviews the draft amendment to Annex 3 contained in the AMOSSG/3-SN No. 2.

1.	REMARKS ON THE PROPOSED AMENDMENT 73 TO ANNEX 3

1.1	The result of the requested review of the AMOSSG/3 - SN No.2 is as follows:

1.2	Appendix A

1.2.1	General remark: The proposed amendment of Annex 3 will probably become into force at the end of 2004 and will be valid for a couple of years. However, during the period till Amendment 74 (2007) will be implemented, developments in the automation of observations like cloud amount and -type and products like AUTO METAR and local reports, -TREND and -TAF will go on. Cuts in budgets, lack of observers and technology development forces MET Services to follow this route of automation.

1.2.2	In the present draft Amendment 73 the aspect of automation is touched only very little. The AUTO METAR is allowed only during the non-operational hours of the aerodrome till 2 hours from the start of the operations. This policy is rather conservative and does not take enough into account the developments to be expected in the coming years. It will be foreseeable that in the near future too many States have to file differences using automated systems and products. So, in Amendment 73 it should be reflected that automated observations as AUTO METARs and AUTO local reports will be allowed as official products during the non-operational and the operational hours of the aerodrome. This will mean a change in the policy of ICAO, IATA and IFALPA; however a change which an open view to the future.

1.2.3	The detailed comments are as follows:

—	4.1.8:	When integrated automatic systems are used it should be possible to switch of the data from a single or integrated sensor(s) and replace it by ///. However, it will not be possible to insert manual values for all sensors or integrated sensors, as these values are not always known (e.g. pw-values derived from radar, visibility, etc.).	Most of the time a failure of the integrated automatic system will mean that the whole observing system will be down. The insertion of manual values will be out of question. Proposal: delete the last sentence;

—	4.1.9: Proposal: identical to 4.1.8;

—	4.2.3:	These METAR's can be "AUTO METAR's". Proposal: This should be mentioned in this paragraph e.g. " …. reports in the (AUTO) METAR code form ….".	Note: see also 4.13.1;

—	4.3.3:	These SPECI's can be "AUTO SPECI's". Proposal: "…. reports in the (AUTO) SPECI code form…". Note: see also 4.13.1;

—	4.5.4: Deployment of additional sensors is not a problem. However, from the practical point of view, the way to report and to use this additional information is not clear. Note: The expression "best practicable indication" in the Recommendation and the Note, seems not to be in line with the requirement of representativeness of the wind measurement for the whole runway (para. 4.5.2);

—	4.5.5: "Surface wind displays relating to each sensor shall be located" may raise the impression that every sensor will be displayed on its own display and that is not the meaning of this sentence. Proposal: change the text as follows: "Surface wind from one or more sensors shall be displayed in the meteorological station and in a corresponding way in the appropriate air traffic service units. The display ... etc." Note: the other paragraphs where displays are mentioned should be changed accordingly. For harmonizing the display of the wind information in the air traffic service unit and to be sure that the presented values are representative it may be appropriate to add a minimum "update frequency". Proposal: add a separate paragraph (Recommendation): "The minimum update frequency for the display of the wind information in the air traffic service unit should be at least 15 sec;

—	4.5.7:	In this paragraph the averaging of the gust and the gust direction should be mentioned also. Proposal: add to the paragraph: "c) 3 seconds for the variation from the mean wind speed (gust) in accordance with par. 4.5.8 c) for local routine and special reports and for reports in the METAR/SPECI code forms.";

—	4.5.8: b): It must be clear that both the variations described in b 1) and b 2) must be related to the preceding 10 min period. Proposal: add in the first sentence after the word "shall" the words "refer to the preceding 10 minutes period and be …". Delete in b 1) the words "during the past 10 minutes". After studying this paragraph we have come to the conclusion that it could be formulated in a more simple and better understandable way, such as: Proposal: "1) when the total variation is less than 180 and the wind speed is more than 6 km/h (3 kt) the mean wind direction shall be reported along with the directional variation expressed as the two extreme directions in clockwise order between which the wind has varied; 2) the wind direction shall be reported as variable with no mean wind direction when the total variation is 180 or more, or when the total variation is less than 180 and the wind speed is 6 km/h (3 kt) or less.".	c.: in WMO or in ICAO documents no clear definition of gust is available. Proposal: to address the lack of a proper definition of gust to WMO. c.: The minimum mean wind speed value from which the gust has to be reported should be mentioned. Proposal: add the sentence "and the mean wind speed is 10 kt or more." Note: see also the SN on gust reporting. e.1: It is not clear why the variations from the mean wind direction and wind speed occurring since the discontinuity, have to be derived from the actual measured values and not from the 2-min averages. Sample frequencies are different per type of sensor;

—	4.5.9:	It is not quite clear why this paragraph could not be a Standard. Proposal: upgrade paragraph 4.5.9 to a Standard;

—	4.6.4:	The end of the paragraph is not in line with the text of paragraph 4.6.2. Proposal: delete "e.g. lift-off";

—	4.6.5:	The corresponding para. for RVR (4.7.9) is a Standard. It is not clear why this paragraph is not a Standard also. Proposal: upgrade paragraph 4.6.5 to a standard in line with the paragraph 4.7.9 related to RVR;

—	4.6.6:	The corresponding para. for wind 4.5.7. and RVR 4.7.11 is a Standard. It is not clear why this par. is not a Standard also. Proposal: upgrade to a Standard in line with the paragraph wind 4.5.7. and 4.7.11 related to RVR;

—	4.6.9 a): For long runways more than 3 sensor sites will be installed. In that case there is no "mid-point" but a "mid-section" of the runway. This can be considered as the section between 1 500 m from the defined thresholds of the runway. Proposal: insert after "mid-point" the words "or mid-section for long runways, e.g. MID-1 and MID-2, and…". Note: The code-group is quite similar to the RVR. It should be made clearer that VIS is mentioned here in order to identify in a unique way the measured values;

—	4.6.10: The difference between a) and d) is not clear. In both the "lowest visibility" will be reported without direction. Proposal: delete para. 4.6.10 d);

—	4.7.2: Is it logical to let this paragraph be a Recommendation, while paragraph 4.7.4 a) is a Standard?

—	4.7.3 c): In line with the par. 4.6.9 a) the "mid section" should be inserted. Proposal: insert the words "or mid-section for long runways" after the word "mid-point";

—	4.7.6: In line with the para. 4.6.9 a) and para. 4.7.3 a) the "mid section" should be inserted. Proposal: insert the words "or mid-section" after the word "mid-
point";

—	4.7.12: From the results of the questionnaire by the PT/METAOP it was clear that in the EUR Region States use the 100% lamp setting (> 50%) and others use tables (day-twilight-night). Only a couple of States use the actual lamp setting. The draft-Conclusion of the METG was adopted by the EANPG asking the OPS Panel to consider the use of 100% lamp setting. Proposal: Regarding this development the text of this paragraph should be reworded;

—	4.7.15: The figure of 2 000 m is not in line with paragraph 4.7.3. Moreover paragraph 4.7.3 is a standard and 4.7.15 a recommendation. Proposal: in order to harmonize this two para. both should be a Standard and the figures should be made equal;

—	4.7.17: c) : In line with the para. 4.6.9 a) and par. 4.7.3 a) the "mid section" should be inserted. Proposal: insert the words "or mid-section" after the word "mid-point". Note: see note concerning paragraph 4.6.9 a);

—	4.7.18 b): In the text of this paragraph is stated "more than one runway available". These words will lead into endless discussions as it can be interpreted as "all the runways, which are available, but not all of them will be used" or "the runways that will be in operational use". Proposal: delete the words "such runways" and insert the words "the runways in use";

—	4.8: General remark: the references made to paragraphs 4.8.5 and 4.8.6 should be paragraphs 4.8.8 and/or 4.8.9;

—	4.8.5: The use of additional sensors, systems or techniques will be used for the observation of present weather phenomena, will be excluded by this Recommendation. Proposal: add the words "or other available systems and techniques";

—	4.8.6: Corresponding displays should be located in the appropriate air traffic services units. The necessity for this is unclear to me, as there is no need to duplicate the complete equipment of the weather room into the air traffic services units. Also in the case that a combination of techniques will be used to derive the pw-values it will not be possible and not desirable to follow this Recommendation. Proposal: delete the words "with corresponding …. units";

—	4.8.8/9: When a AUTO METAR will be produced, for which a present weather sensor(s) is used without the intervention of a human observer, a change in the use of the code for the description of present weather in this AUTO METAR can be expected. On the one hand, some elements will not be detected by a pw- sensor e.g. FC or those elements with the prefix VC. This will be not problematic, as one will not use the "none applicable code combination". On the other hand, it is known that the detection of the precipitation type by a pw-sensor is not correct under all circumstances, e.g. the precipitation to be detected is outside the definitions of the sensor. In those cases the pw-sensor will report "unidentified precipitation". Proposal: insert in the present weather code "undefined precipitation: PP or UP". An additional point: perhaps it should be discussed if minimum specifications for the elements to be reported via the AUTO METAR should be developed;

—	4.9.2: The middle marker has been disappeared already from a lot of aerodromes. Proposal: delete "middle-marker" and insert "the area of 900 m to 1200 m from the threshold of the runway" as stated in paragraph 4.9.5. The note can be deleted;

—	4.9.4: The items not directly measurable will be determined for calculation. Proposal: delete the words "directly measurable" and insert "to be determined" as it will be a calculation;

—	4.9.5-7: There are no SARPs for the cloud amount and cloud type. Should they be developed?

—	4.9.10 c): The deletion of TCU in the METAR is agreed. However, to be consequent it should be deleted also in the local routine and special reports. Proposal: delete item c);

—	4.10.2: Note: no distinction is made in the representativeness of the temperature to be reported in the METAR and local reports. However, on big airports there could be a difference for the temperature regarding the runways in use and the "general temperature" reported in the METAR;

—	4.10.3: It will be more logical to use only 1 indication for both the METAR and the local report. Proposal: delete this paragraph 4.10.3;

—	4.11. Note: a paragraph about the representativeness is missing;

—	4.12.2: See the remark concerning paragraph 4.1.8. Beside this remark it is not clear if the "automatic observing equipment" is different from the "integrated automatic systems" as is mentioned in paragraphs 4.1.8/9/10;

—	4.13.1: In the text is stated that the METARs issued during the 2-hour period prior to the aerodrome resuming operations should be similar to those issued during the operational hours of the aerodrome. This means that the human observations have to start 2 hours before the opening of the aerodrome. As this will be a "nightmare" for the work schedule of the observers and taking into account that the original meaning of this issue saying that in order to be able to produce a TAF a minimum of 2 observations should be available, it should be made possible to use AUTO METARs for this purpose; Proposal: add to the last sentence "or issued as AUTO METAR";

—	4.14.1 h): In line with the par 4.9.10 c) TCU should be deleted. Proposal: delete "towering cumulus clouds and";

—	4.14.3 c): Note: the reference paragraphs should be 4.8.8 and 4.8.9;

—	6.2.5: Regarding the fact that AUTO METARs will be used more and more, and taking into account also that due to the development of modern techniques the quality of the AUTO METAR will improve continuously and no observers can be available on the schedule of 2 hrs prior to the opening hours of the airport (see comment on paragraph 4.13.1), the Note should be deleted. Proposal: delete the Note.

1.3	Appendix B

1.3.1	General remark. The prevailing visibility, both the American and the Austrian method and the proposal of France, were discussed in depth by the Meteorology Group (METG) of the EANPG in September 2001. The outcome of this discussion was a "general agreement that there was no need to introduce the prevailing visibility but that automated systems, when available, should be used as a complement to the human observation to improve the representativeness of the observations".

1.3.2	In practice, today the prevailing visibility North American method is implemented only in the United States and Canada for those airports with human observers. The airports with an automated observing system only, will report "runway visibility". To avoid that observations and "forecast" (prevailing visibility) of visibility will be mixed up and to meet the requirement to use the existing systems in a better way, it is recommended to introduce the "runway visibility" instead of prevailing visibility. Note: see SN- No. 8 on prevailing visibility. Proposal: insert "runway visibility" instead of "prevailing visibility".

2.	ACTION BY THE GROUP

2.1	The AMOSSG is invited to consider the proposals and remarks to the proposed Amendment 73 during its deliberations.

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