AMOSSG/5-SN No. 18

21/3/05

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

PROPOSAL FOR PRESENT AND RECENT WEATHER PHENOMENA REPORTING CRITERIA

(Presented by Bill Maynard)

SUMMARY
Present and recent weather reporting criteria are evaluated in consideration of user and forecasting requirements and the current capabilities of meteorological observing systems. An alternative set of criteria is proposed.

1.	INTRODUCTION

1.1	The Aerodrome Meteorological Observing Systems Study Group (AMOSSG), was created to support the International Civil Aviation Organization (ICAO) secretariat, in reviewing and updating the international standards and recommended practices for meteorological observations and reports.

1.2	Task 6, for the AMOSSG, it to: Revise the weather phenomena to the reported under "present weather" and "recent weather".

1.3	Previous attempts to review the present and recent weather reporting criteria, by evaluating each reportable phenomena, on a case-by-case basis, have proven unsuccessful. Although some members of the AMOSSG group had argued that squalls (SQ) and ice pellets showers (SHPL) should be removed from the list they could not build a consensus.

1.4	This paper proposes an abbreviation of the current present and recent weather criteria based upon consideration of:

a)	current State practices regarding the use of fully automated system during operational hours;

b)	b) flight planning requirements;

c)	TAF support requirements;

d)	necessity appropriate to the climate of the aerodrome;

e)	feasibility (economic and technological practicability); and

f)	stated concerns and requirements from international aviation users.

2.	DISCUSSION

2.1	Background

2.1.1	The criteria for the reporting of present and recent weather phenomena are stated in ICAO Annex 3, Section 4.6.4 as follows:

—	4.6.4.1 The present weather occurring at the aerodrome and/or its vicinity shall be observed and reported as necessary.

—	4.6.4.2 Recommendation. — For local routine and special reports, the present weather information should be representative of conditions at the aerodrome.

—	4.6.4.3 Recommendation. — For METAR and SPECI, the present weather information should be representative of conditions at the aerodrome, and for certain specified present weather phenomena, in its vicinity.

—	4.6.4.4 Recommendation. — Where observations are made using automatic systems, provision should be made for manual insertion of those present weather elements which cannot be determined adequately by that equipment.

2.1.2	It is notable, from consideration of 2.1.1, that necessity is a basis for determining the required capabilities for present and recent weather reporting. Therefore, the expected climate at a given site is proposed as a basis for limiting the present weather reporting requirements. For example, lack of necessity would justify the lack of ability to detect snow or ice accretion is tropical climates.

2.1.3	Appendix A to this paper provides details regarding further ICAO recommendations and standards for present and recent weather reporting criteria as found in Annex 3, Part II, Appendix 3, Section 4.4.

2.2	Current State practices

2.2.1	At least five States currently permit the use of fully automated observing systems for the reporting of present weather. The current capabilities and reporting practices of these systems were compared and any reporting capabilities which were common to all these systems are considered as having been demonstrated as being achievable and practicable. The common capabilities to the automated system used in these state, where known, are proposed as the minimum capability in an future international standard.

2.2.2	The known current reporting practices of States which currently permit the use of fully automated systems, during operational hours, are:

a)	in the case of Canada, the current list of reportable weather criteria includes; RA, SN, DZ, FZDZ, FZRA, UP and SHGR (for hail); each of which can be of light, moderate or heavy intensity;

b)	in the case of the United States, based upon the State Difference filed against Annex 3, (amendment 72) sections 4.8.4 and 4.8.5. the following are not reported in comparison with the list in Appendix A: DZ, PL, IC, SG, GR, GS, SA, DU, FU, VA, PO, SQ, FC, DS, SS nor are any of the following characteristics; SH, DR, MI, BC, PR; and

c)	in the case of France, based upon the State Difference filed against Annex 3, (amendment 72) sections 4.8.4 and 4.8.5. the following are not reported in comparison with the list in Appendix A: SG, PL, GR, GS, DS, SS, TS, PO, FC, SA, DU, HZ, FU, VA and SQ. Furthermore, the label VC is not used.

2.2.3	It is assumed, subject to confirmation, that each of the five States also allows for the reporting of unknown precipitation type (UP). This practice is also in accordance with Annex 3, Appendix 3, Section 4.9.1.3.

2.2.4	Based on 2.2.1 to 2.2.3, the present weather reporting capabilities and practices common to all systems used in Canada, France and the United States (based on available information) are: rain, freezing rain, snow and unknown precipitation types; each of which can be reported as being of a light, moderate or heavy intensity. This yields a total of 12 reportable present weather conditions in addition to the case of no reportable weather, with numerous combinations possible.

2.3	Consideration of flight planning requirements

2.3.1	Pertinent excerpts from ICAO Annexes, primarily Annex 6, relating to flight planning are included in Appendix B. Although "flight planning" is not specifically defined in the Annexes, several essential components are established.

2.3.2	For the purpose of this paper, there are no flight planning requirements for the reporting of any phenomena other than those currently specified in ICAO Annexes.

2.3.3	From Annex 6, the "aerodrome operating minima" are expressed in terms of visibility and/or runway visual range and, if necessary, cloud conditions (see Appendix B for details). With the exception of the presence of icing conditions (freezing fog or freezing precipitation) no other present weather conditions are specifically mentioned in Appendix 6 as being essential to the flight planning process.

2.3.4	Based on a review of flight planning requirements we can conclude that the present weather reporting requirements must include any potential source of ice accretion including both freezing fog and freezing precipitation as well as any other present weather phenomena which is necessary to diagnose or forecast the presence of any low cloud or low visibility.

Note: Ice accretion may occur and has been detected by automated sensors in the absence of precipitation or fog, typically from frost alone. It remains desirable to seek a quantitative assessment of what ice accretion rate and/or amount is of significance to aviation so that reporting algorithms can be set to respond appropriately.

2.3.5	Based on flight planning considerations; the list of criteria currently reported by automated systems (section 2.2.4) is inadequate and should be appended to include reports of the presence or absence of freezing fog or ice accretion.

2.4	TAF support requirements

2.4.1	The forecast product which is used to determine the suitability of destination or alternate aerodromes for an intended flight is the TAF. The present weather reporting criteria must be sufficient to support the production of the TAF and must provide notification of any significant changes that may prompt an amendment to the TAF.

2.4.2	The characteristics and limitations of weather reporting and forecasting should be carefully considered in this review. Note that based on section 6.1.1 of Annex 3, the TAF "shall be understood by the recipient to be the most probable value which the element is likely to assume during the period of the forecast." Furthermore, 4.1.9 states that "Owing to the variability of meteorological elements in space and time, to limitations or observing techniques and to limitation caused by the definitions of some of the elements, the specific value of the elements given in a report shall be understood by the recipient to be the best approximation to the actual conditions at the time of the observation."

2.4.3	For this paper, the measure of the acceptability, for TAF purposes, of any present weather reporting criteria is their ability to facilitate forecasts of the "most probable value of the weather" and to prompt timely TAF amendments, when necessary.

2.4.4	The recommendations in Annex 3, Appendix 5 regarding the weather phenomena that prompt TAF amendment or change groups (section 1.2.3 refers) are accepted as a measure of the significance of changes to the current state of the weather, as follows:

The criteria used for the inclusion of change groups in aerodrome forecasts or for the amendment of aerodrome forecasts should be based on the following…

c)	when any of the following weather phenomena or combinations thereof are forecast to begin or end or change in intensity:

— freezing precipitation

— moderate or heavy precipitation (including showers thereof)

— duststorm

— sandstorm

— other weather phenomena given in Appendix 3, 4.4.2.3 only if they are expected to cause a significant change in visibility;

d)	when the onset or cessation of any of the following weather phenomena or combinations thereof are forecast to begin or end:

— ice crystals

— freezing fog

— low drifting dust, sand or snow

— blowing dust, sand or snow

— thunderstorm (with or without precipitation)

— squall

— funnel cloud (tornado or waterspout)

Note: The other weather phenomena given in Appendix 3, 4.4.2.3 are shown in Appendix A.

2.4.5	Four conclusions are drawn upon considering the TAF amendment and change group criteria:

—	First, the TAF amendment criteria in excess to what is needed to support flight planning in accordance with Annex 6 standards for flight planning which are predicated upon cloud, visibility and icing conditions (see Appendix B).

—	Second, no known automated system can report weather inclusive of all the criteria listed for TAF amendments. In particular, automated systems cannot currently distinguish between dust or sand.

—	Third, they support the inclusion of thunderstorms and freezing fog as essential present weather reporting criteria.

—	Fourth, the current TAF amendment criteria do not identify changes between; rain and drizzle, freezing rain and freezing drizzle or the presence of absence of hail or ice pellets; contrary to the valid forecast, as requiring a potential amendment.

2.4.6	It has been demonstrated that thunderstorms are detectable by automated methods and they represent a hazard to aviation. Therefore it is concluded that they should be a mandatory reportable present weather condition.

2.4.7	In consideration of 2.4.1 to 2.4.6, it is concluded that METAR/SPECI should be representative of the current weather inclusive of thunderstorms (at or in the vicinity of the aerodrome), freezing fog and ice accretion. However, reporting of the changes between drizzle and rain, whether freezing or not, are not required to support flight planning.

2.4.8	A summation of the present weather requirements derived by consideration of all the aforementioned factors is shown in Appendix C.

2.4.9	The TAF amendment criteria should be evaluated in conjunction with any review of present and recent weather reporting criteria with the intent of making them common.

Note: The task of seeking to create common present weather reporting and TAF amendment criteria for present weather is a current AMOSSG tasking to the Secretariat (listed as Task 1 on the list of future work for the AMOSSG).

2.5	Consideration of necessity

2.5.1	Consideration should be given to allowing States to abbreviate any proposed present weather reporting requirements, based on climate factors. Clearly, there is no need to have the ability to report snow or freezing precipitation in tropical climates nor should thunderstorm detections ability be needed in the high Arctic.

2.5.2	It is suggested that the intent of 2.5.1 could be met by retaining the current phrase "as necessary" with the specific requirements for present weather reporting. However, consideration should be given to qualifying that necessity should be based upon the expected climate for the site.

2.6	Feasibility

2.6.1	Any proposed present weather reporting criteria must address the following concerns:

a)	if the criteria are too demanding, then:

1)	many States may simply disregard the international standard in favour of continuing their current practices;

2)	manufacturers may not be able to respond to impossible requirements;

3)	the associated costs would be unnecessarily high; and

4)	increased complexity and cost could lead to no service being available in some areas (that is, the alternative to meeting the standard could be no service at all).

b)	if the criteria are insufficient, then:

1)	many States may simply disregard the international standard in favour of continuing their current practices;

2)	some operational automated systems may not meet flight planning or forecasting requirements; and

3)	there may be inadequate incentive to continue developing new technology.

2.6.2	It is the subjective view of the author of this paper, upon considering these concerns, that any increase in the requirements made for automated reporting of present and recent weather phenomena should be relatively modest compared to what is currently provided by some countries. The risk of excessive costs or inadequate networks is too high if requirements are made unrealistically high. Based on this assessment the list established by Appendix C, is sufficient.

2.7	Consideration of consultations with international pilots

2.7.1	International pilot representatives stated the following concerns and requirements in response to an earlier proposal which would have revised the list of essential weather reporting criteria to just 6 phenomena (shown in Appendix D):

a)	any new criteria for present and recent weather should be a subset of the current criteria, therefore, no new weather types such as freezing snow or ice accretion in the absence of precipitation or fog should be introduced;

b)	there is a need to differentiate between rain and drizzle;

c)	when more than one present weather type is occurring at the same time then all types should be reported;

d)	the rate of snowfall should be reported;

e)	snowfall accumulations should be reported on at least an hourly basis;

f)	ice pellets should remain as a reportable phenomena; and

g)	it is not necessary to report recent weather if the relevant weather was included in the most recent report.

Note:— This list is based upon preliminary feedback from IATA only.

2.7.2	It is noted that the proposed new criteria shown in Appendix C address all of these concerns except they would:

a)	not differentiate between drizzle and rain;

b)	not provide reports of snowfall accumulations; and

c)	not report ice pellets.

2.7.3	More information should be sought to explain the reasons for the stated requirement to differentiate between drizzle and rain, however, due to a lack of a requirement for this in the current ICAO Annex 6 flight planning standards or Annex 3 TAF amendment criteria requirements, it was not included in this paper.

2.7.4	Furthermore, the results of tests to evaluate the ability of instrumentation to differentiate between drizzle and rain, as documented in World Meteorological Organization Technical Document No. 887 (WMO Intercomparison of Present Weather Sensors/Systems: Canada and France, 1993-1995) show serious limitations to several sensors and at best mixed results. It may be better to focus on detecting the liquid or supercooled phases and less on trying to measure the droplet size and fall speeds.

2.7.5	Further, it is proposed that Annex 3 should respond to changes in the Annex 6 standards related to flight planning rather than be the originator of new flight planning requirements.

2.7.6	Snowfall accumulations are of interest to pilots due to the association with runway conditions. Based on Annex 3, Appendix 3, 4.8.1.4 (b), the provision of information on the state of the runway is the responsibility of the appropriate airport authority. Although this information can be appended to the METAR / SPECI as supplementary information it is not the responsibility of the meteorological service to provide this information.

2.7.7	This paper argues for consistency with the current ICAO TAF amendment criteria as the measure of the need to include ice pellets as a mandatory element of present weather reporting. However, it should be noted that the existence of ice pellets at the surface is indicative of freezing rain aloft. The existence of freezing rain aloft may limit flight operations in accordance with the Annex 6 standards for flight planning (see Appendix B). It is assumed that most automated systems will tend to report ice pellets as rain (similar size and fall speeds) which, as a result, would then be reported as freezing rain in below freezing temperatures thereby ensuring an equivalent level of safety.

2.7.8	The existence of thunderstorms is a precondition for the existence of damaging hail. Furthermore, good airmanship requires that all thunderstorms be avoided by a wide margin. Therefore the ability of any automated system to detect and report thunderstorms is assumed to provide an adequate warning of the possibility of hail. It should be noted that remote sensing techniques such as lightning detection, weather radar and satellite imagery are very effective at identifying the presence of significant thunderstorms and for detecting the presence of hail.

2.8	Alternative criteria for recent weather reporting

2.8.1	The current criteria for recent weather reporting (as detailed in Appendix A to this paper) were reviewed while in consideration of current State practices, flight planning requirements, forecasting requirements and feasibility.

2.8.2	This paper concludes that there is no requirement to report recent weather where there is a continuous weather watch capable of providing timely warning of changes in weather conditions which are of significance to aviation. This conclusion is supported, conditionally, by the results of the limited consultations with international aviation pilots who, alternatively, stressed the need for accurate and timely weather information.

2.9	Proposed new present and recent weather reporting criteria

2.9.1	The net result of the consideration of all factors detailed in 2.2 to 2.8, above, suggests that the present and recent weather reporting criteria can be abbreviated to those shown in Appendix C.

2.10	Implications

2.10.1	If new present and recent weather criteria similar to those in Appendix C are adopted as the core standard for all present and recent weather reporting there may be a reduction in the expectations from human observers. There are at least two resulting options:

a)	disregard this issue and establish the new criteria as the full set of reportable weather in the interest of providing only essential information to pilots in an internationally consistent format; or

b)	develop enabling provisions that allow for value added reporting of some, or all, of the current weather phenomena that would no longer be mandatory.

2.10.2	Option b) from 2.10.1 is favoured as it would support the continuation of reporting practices that may improve efficiency and would also accommodate the practices of States that include additional information for non-aviation practices.

2.10.3	The criteria in Appendix C would perpetuate a difference between automated and human observations with respect to the allowance for automated systems to report unknown precipitation type. Three options have been identified to address this:

a)	remove unknown precipitation type from the core standard and provide enabling clauses to permit it as an option for automated systems only;

b)	permit human observers, as well as automated systems, to report unknown precipitation; and

c)	remove the allowance to report unknown precipitation and require automated systems to report the most likely phase type occurring regardless of the confidence level of the assessment.

Option a) is favoured based on the assessment that current technology will not always report all phase types accurately. The principle that no data is better than erroneous data is followed.

3.	ACTION BY THE WORKING GROUP

3.1	The working group is invited to:

a)	comment on the review criteria used for this paper and note any additional criteria that should be considered (section 1.4);

b)	review and correct, as necessary, the description of the current capabilities of the fully automated systems which are currently being used during the operational hours of aerodromes (section 2.2.2);

c)	comment on the interpretation of the international standards for flight planning (section 2.3);

d)	comment on the concept of allowing States to modify the capabilities of their automated systems based on climate factors (section 2.5);

e)	comment on the concerns and requirements of international pilots in particular the requirements to distinguish between rain and drizzle (section 2.7.1);

f)	consider and comment on the proposal that neither ice pellets nor hail need to be included as core reporting requirements (section 2.7.8);

g)	comment on the implications of an abbreviation present weather reporting criteria on human observers (section 2.10.1);

h)	comment on the appropriate means for addressing the proposed allowance for automated systems to report unknown precipitation type (section 2.10.2.1);

i)	consider and comment on the conclusion that there is no requirement for the reporting of recent weather; and

j)	review and comment on the adequacy of the present and recent weather reporting criteria which emerged as a result of this review (Appendix C).

— — — — — — — —

Drizzle (DZ)

Rain (RA)

Snow (SN)

Snow grains (SG)

Ice pellets (PL)

Ice crystals (IC) (very small ice crystals in suspension, also known as diamond dust) – reported only when visibility is 5 000 m or less.

Hail (GR) – reported when diameter of largest hailstone is 5 mm or more.

Small Hail or Snow Pellets (GS) – reported when diameter of largest hailstones is less than 5 mm.

Obscurations (hydrometeors)

Fog (FG) reported only when visibility is less than 1 000 m, except when qualified by "MI", "BC", "PR" or "VC".

Mist (BR) reported when visibility is at least 1 000 m but not more than 5 000 m.

Obscurations (lithometeors)

The following should be used only when the obscuration consists predominantly of lithometeors and the visibility is 5000 m or less except "SA" when qualified by "DR" and volcanic ash.

Sand (SA)

Dust (DU)

Haze (HZ)

Smoke (FU)

Volcanic Ash (VA)

Other phenomena

Dust / sand whirls (dust devils) PO

Squall	SQ

Funnel Cloud (tornado or waterspout) FC

Duststorm DS

Sandstorm SS

Characteristics

Thunderstorm (TS) – Used to report a thunderstorm with rain "TSRA", snow "TSSN", ice pellets "TSPL", hail "TSGR", or small hail and/or snow pellets "TSGS" or combinations thereof, for example, "TSRASN". When thunder is heard or lightning is detected at the aerodrome during the 10-minute period preceding the time of observation but no precipitation is observed at the aerodrome, the abbreviation "TS" should be used without qualification.

Shower (SH) – Used to report showers of rain "SHRA", snow "SHSN", ice pellets "SHPL", hail "SHGR", small hail and/or snow pellets "SHGS", or combinations thereof, for example "SHRASN". Showers observed in the vicinity of the aerodrome (4.4.2.5) should be reported as "VCSH" without qualification regarding the type or intensity.

Freezing (FZ) – Supercooled water droplets or precipitation, used only with FG, DZ and RA.

Blowing (BL) – Used to report DU, SA or SN raised by the wind to a height of 2 m (6 ft) or more above ground.

Low Drifting (DR) – Use with DU, SA or SN raised by the wind to less than 2 m (6 ft) above ground level.

Shallow (MI) – Less than 2 m (6 ft) above ground level.

Patches (BC) – Fog patches randomly covering the aerodrome.

Partial (PR) – A substantial part of the aerodrome covered by fog while the remained is clear.

Intensity

Used only with DZ, GR, GS, PL, RA, SG and SN (or in combinations involving these present weather types; in these cases, intensity refers to precipitation in accordance with 4.4.2.6); DS and SS (in the cases of DS and SS, only moderate and heavy intensities to be indicated).

Light (-)

Moderate

Heavy (+)

Proximity

Vicinity (VC) – Not at the aerodrome by not further away than approximately 8 km from the aerodrome perimeter and used only in METAR and SPECI with DS, SS, FG, FC, SH, PO, BLDU, BLSA, BLSN, TS and VA.

Simultaneous Multiple Weather Types (4.4.2.6)

In local routine and special reports and in METAR and SPECI, one or more up to a maximum of three of the present weather abbreviations given in 4.4.2.3 and 4.4.2.4 should be used, as necessary, together with an indication, where appropriate, of the characteristics and intensity or proximity to the aerodrome, so as to convey a complete description of the present weather of significance to flight operations. In reporting this information, the indication of intensity or proximity as appropriate, should be reported first followed respectively by the characteristics and the type of weather phenomena. Where two different types of weather are observed, they should be reported in two separate groups, where the intensity or proximity refers to the weather phenomena which follows the indicator. However, the different types of precipitation occurring at the time of observation should be reported as one single group with the dominant type of precipitation reported first and preceded by only one intensity qualifier which refers to the intensity of the total precipitation.

Recent weather reporting criteria (Appendix 3, 4.8.1.1)

Recent freezing drizzle (REFZDZ)

Recent freezing rain (REFZRA)

Recent Drizzle (REDZ)

Recent Rain (RERA)

Recent Snow (RESN)

Recent snow grains (RESG)

Recent hail (REGR)

Recent small hail and / or snow pellets (REGS)

Recent ice pellets (REPL)

Recent rain showers (RESHRA)

Recent snow showers (RESHSN)

Recent snow grain showers (RESHSG)

Recent ice pellet showers (RESHPL)

Recent hail showers (RESHGR)

Recent small hail and / or snow pellet showers (RESHGS)

Recent Ice crystals (REIC)

Recent blowing snow (REBLSN)

Recent sandstorm (RESS)

Recent duststorm (REDS)

Recent thunderstorm (RETS)

Recent funnel cloud (tornado or waterspout) (REFC)

Recent volcanic ash (REVA)

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AMOSSG/5-SN No. 18

Appendix B

APPENDIX B

EXCERPTS FROM ICAO ANNEXES CONCERNING FLIGHT PLANNING

From Annex 2

Section 2.3.2 Pre-flight action

Before beginning a flight, the pilot-in-command of an aircraft shall become familiar with all available information appropriate to the intended operation. Pre-flight action for flights away from the vicinity of an aerodrome, and for all IFR flights, shall include a careful study of available current weather reports and forecasts, taking into consideration fuel requirements and an alternative course of action if the flight cannot be completed as planned.

Section 4.2 Visual Flight Limits

4.2 Except when a clearance is obtained from an air traffic control unit, VFR flights shall not take-off or land at an aerodrome within a control zone, or enter the aerodrome traffic pattern:

a)	when the ceiling is less than 450 m (1 500); or

b)	when the ground visibility is less than 5 km.

From Annex 3 definitions

Meteorological Information. Meteorological report, analysis, forecast, and any other statement related to existing or expected meteorological conditions.

Operational flight plan. The operator's plan for the safe conduct of the flight based on consideration of aeroplane performance, other operating limitations and relevant expected condition on the route to be followed and at the aerodrome concerned.

Operational planning. The planning of flight operations by an operator.

From Annex 6

Definition:

Aerodrome Operating Minima. The limits of usability of an aerodrome for:

a)	take-off, expressed in terms of runway visual range and/or visibility and, if necessary, cloud conditions;

b)	landing in precision approach and landing operations, expressed in terms of visibility and/or runway visual range and decision altitude/height (DA/H) as appropriate to the category of the operation;

c)	landing in approach and landing operations with vertical guidance, expressed in terms of visibility and/or runway visual range and decision altitude/height (DA/H); and

d)	landing in non-precision approach and landing operations, expressed in visibility and/or runway visual range, minimum descent altitude/height (MDA/H) and if necessary, cloud conditions.

Instrument Meteorological Conditions. Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling*, less than a minima specified for visual meteorological conditions.

Visual Meteorological Conditions. Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling*, equal to or better than specified minima.

Note.— The specified minima are contained in Chapter 4 of Annex 2.

4.3.5 Weather conditions

4.3.5.1 A flight to be conducted in accordance with the visual flight rules shall not be commenced unless current meteorological reports or a combination of current reports and forecasts indicate that the meteorological conditions along the route or that part of the route to be flown under visual flight rules will, at the appropriate time, be such as to render compliance with these rules possible.

4.3.5.2 A flight to be conducted in accordance with instrument flight rules shall not be commenced unless information is available which indicates that conditions at the aerodrome of intended landing or, where a destination alternate is required, a least one destination alternate aerodrome will, at the estimated time of arrival, be at or above the aerodrome operating minima.

Note.— It is the practice in some States to declare, for flight planning purposes, higher minima for an aerodrome when nominated as a destination alternate than for the same aerodrome when planned as that of intended landing.

4.3.5.3 A flight to be operated in known or expected icing conditions shall not be commenced unless the aeroplane is certificated to cope with such conditions.

4.3.5.4 A flight to be planned or expected to operate in suspected or known ground icing conditions shall not take off unless the aeroplane has been inspected for icing and, if necessary, has been given appropriate de-icing/anti-icing treatment. Accumulation of ice or other naturally occurring contaminants shall be removed so that the aeroplane is kept in an airworthy condition prior to take- off.

— — — — — — — —

AMOSSG/5-SN No. 18

Appendix C

APPENDIX C

PROPOSAL FOR ABBREVIATED CRITERIA FOR PRESENT AND RECENT WEATHER REPORTING

Proposal for abbreviated criteria for present and recent weather reporting

a) Present Weather

Light Rain (-RA)

Rain (RA)

Heavy rain (+RA)

Light Freezing Rain (-FZRA)

Freezing Rain (FZRA)

Heavy Freezing rain (+FZRA)

Light snow (-SN)

Snow (SN)

Heavy snow (+SN)

Fog (FG)

Freezing fog (FZFG)

Thunderstorm (TS)

Vicinity (VC) — used only with TS when not at the aerodrome but not farther away than approximately 8 km from the aerodrome perimeter.

Automated Systems would be permitted to report unknown precipitation type of a light, moderate or heavy intensity.

Notes: —	(1) TS would be reported whether detected at, or in the vicinity of the aerodrome, all others would be reported only if at the aerodrome.

(2) All present weather occurring at the time of the observation would be included in the report.

(3) Supplementary information would be included in accordance with regional air navigation agreement, and

(4) There would be no requirement to report recent weather.

(5) All freezing precipitation is reported as freezing rain. No differentiation is made between freezing rain and freezing drizzle. Drizzle would not be a required reporting criteria under any circumstances.

— — — — — — — —

AMOSSG/5-SN No. 18

Appendix D

APPENDIX D

PREVIOUS PROPOSAL FOR ABBREVIATED PRESENT WEATHER REPORTING REQUIREMENTS

a) Present Weather

Rain (RA)

Heavy rain (+RA)

Snow (SN)

Heavy snow (+SN)

Thunderstorm (TS)

Freezing / ice accretion (FZ) – to be reported with (+)RA or (+)SN or TS or, by itself, in the presence of visibility less than 1 000 m and temperature less than 0 C but greater than or equal to -30 C.

b) Recent weather

Recent thunderstorm (RETS)

Recent freezing precipitation or ice accretion (REFZ)

Recent heavy precipitation (RE +RA or RE +SN)

Notes:—	(1) Each of TS and FZ would be reported if observed, in all cases, regardless of the other reported weather phenomena and by themselves if necessary.

(2) TS would be reported whether at, or in the vicinity of the aerodrome, all others would be reported only if at the aerodrome.

(3) Only the dominate precipitation type would be reported for mixed phase precipitation.

— END —