1

METWSG/2-SN No. 10
/ METWSG/2-SN No. 10
2/3/09

METEOROLOGICAL WARNINGS STUDY GROUP (METWSG)

SECOND MEETING

Montréal, 19 to 21 May 2009

Agenda Item / 6: / Wind shear and turbulence warnings
6.1: / Low-level wind shear detection along the approach/take-off paths

STANDARD ATC PHRASEOLOGY

FOR PROVISION OF WIND SHEAR ALERT INFORMATION TO AIRCRAFT

(Presented by CM Shun)

SUMMARY
This paper presents a proposal for the standard phraseology to be used by air traffic control (ATC) units for the provision of wind shear alert information to aircraft in approach, take-off or climb-out area.

1. INTRODUCTION

1.1 The METWSG/1 held in Montreal, 20-22 November 2007 tasked CM Shun and Steve Albersheim to prepare a proposal for standard phraseology to be used by ATC units for the provision of wind shear alert information to aircraft in approach, take-off or climb-out area. In view of the editorial policy of PANS-ATM (Doc 4444), the proposal should consist of no more than 2 or 3 key standard phraseologies. This paper presents the proposal.

2. GUIDING Principles

2.1 Firstly, considering the Human Factors principles, the standard wind shear alert phraseology should be concise for effective and unambiguous communications between ATC and the flight crew, minimizing the need for interpretation. Secondly, the proposed phraseology should be generic enough for use at airports worldwide. Thirdly, the ICAO Abbreviations and Codes in PANS-ABC (Doc 8400) should be used as far as possible for standardization.

2.2 Developed by the US Federal Aviation Administration and adopted by many airports worldwide, two categories of wind shear alert information are provided by automated, ground-based, wind shear remote-sensing or detection equipment to ATC for relay to the flight crew: (a) MICROBURST; and (b) WIND SHEAR. This is in line with Appendix 6 to Annex 3 — Meteorological Service for International Air Navigation para. 6.2.6.

2.3 Appendix 6 to Annex 3 para. 6.2.7 specifies that “Where information from ground-based, wind shear detection or remote-sensing equipment is used to prepare a wind shear alert, the alert shall, if practicable, relate to specific sections of the runway and distances along the approach path or take-off path as agreed between the meteorological authority, the appropriate ATS authority and the operators concerned”. At the Hong Kong International Airport (HKIA), in consultation with IFALPA, an agreement was established between the meteorological authority, civil aviation authority, and the operators concerned that the wind shear alert information to be relayed by ATC to the flight crew would not relate to specific distances along the approach path or take-off path. This is to avoid possible misinterpretation of the alert information generated by the wind shear detection system based on the “First Encounter – Maximum Intensity” principle. Where multiple wind shear events are detected on the same runway corridor (e.g. “+20kt at 3 mile” together with “-45kt at 1 mile”), the wind shear alert information given based on this principle would be “-45kt at 3 mile”, which could mislead the flight crew to think that the alert was an over-warning when only +20kt shear was encountered at 3 mile. To avoid such possible misinterpretation, instead of mentioning the specific distances along the approach path or take-off path, only FINAL APPROACH or DEPARTURE is mentioned in the ATC phraseology at HKIA. Thus the inclusion of such location information in the wind shear phraseology is recommended to be optional.

2.4 As for the microburst alert, while magnitude is currently given in the ATC phraseology at HKIA, upon consulting the wind shear user group in Hong Kong, China, it is considered that information on the sign and magnitude of the microburst is not strictly necessary as the phraseology “MICROBURST” already provides sufficient alert information to the pilot for necessary action and avoidance. It is therefore proposed that the sign and magnitude information may be omitted in the phraseology for microburst.

2.5 There are also other subtle differences in the wind shear alert phraseology currently used by ATC in Hong Kong and US. They include the use of “MINUS”/”PLUS” versus “LOSS”/”GAIN” in the shear magnitude information, mentioning of the runway information or not, and the use of “CAUTION” versus “ALERT”. Examples are:

Wind Shear Alert Presented to ATC / ATC Phraseology for Relay to Flight Crew
07LA MBA -30K APP
(Hong Kong) / caution Microburst minus 30 kt on final approach
07RD WSA +25K DEP
(Hong Kong) / caution Wind shear plus 25 kt on departure
25LA WSA -20K RWY
(Hong Kong) / caution wind shear minus 20 knots on the runway
27A MBA 30K- 3MF
(USA) / Runway 27 arrival, microburst alert, 30 kt loss 3 mile final
27D WSA 25K+ 2MD
(USA) / Runway 27 departure, wind shear alert, 25 kt gain 2 mile departure
09A WSA 20K- RWY
(USA) / Runway 09 arrival, wind shear alert, 20 kt loss on runway

The ATC in Hong Kong prefers the use of “MINUS”/”PLUS” as the controller could read out the “-”/“+” sign of the wind shear directly from the alert message without any interpretation. In case of “LOSS”/”GAIN” as given in the USA, the “-” is interpreted as “LOSS” and “+” is interpreted as “GAIN”. Both “MINUS”/“PLUS” and “LOSS”/“GAIN” are considered equivalent and either one should be given in the phraseology. Following the current convention, “MINUS”/”PLUS” should come before the shear magnitude while “LOSS”/”GAIN” should come after the shear magnitude.

2.6 Regarding the runway information, for conciseness, this information is not mentioned by the Hong Kong ATC as part of the wind shear phraseology since at any one time, there is only one operational runway in use at HKIA. Inclusion of the runway information is proposed to be optional.

2.7 As regards the use of “CAUTION” versus “ALERT”, it is noted that both “CAUTION” and “ALERT” are being used in Doc 4444, e.g. “CAUTION WAKE TURBULENCE” and “TERRAIN ALERT”. The ATC in Hong Kong, China adopted “CAUTION” at the beginning of the wind shear alert phraseology to ensure that the attention of the pilot is immediately drawn to the presence of wind shear. Moreover, “ALERT” may be considered too strong and “CAUTION” is suggested to be more appropriate for wind shear based on pilots’ views. In any case, it is proposed that either “CAUTION” and “ALERT” could be used in the proposed phraseology.

2.8 Finally, the Hong Kong ATC and pilots consider it more informative by adding information about the source of the wind shear alert. It is proposed to include two additional optional phraseologies for qualifying the wind shear alert, namely, “FORECAST” and “REPORTED”. When a wind shear alert is generated by a forecast algorithm rather than detection based on ground-based, wind shear detection or remote-sensing equipment, “FORECAST” could be given. On the other hand, if a wind shear alert is corroborated by pilot report(s), “REPORTED” could be given to add confidence to the alert. For simplicity, if this reported wind shear alert happens to be generated by a forecast algorithm, only “REPORTED” would be given and “FORECAST” will be omitted.

3. proposed standard phraseology

3.1 Table 12.3.1.7 of Doc 4444 outlines the currently adopted phraseology for Meteorological Conditions and appears to be an appropriate place to include the proposed wind shear alert phraseology. Based on the above discussions, and noting that optional phrases may be used (para 12.2.9 of Doc 4444), the group may wish to agree with the following action:

Recommendation 2/ — Standard ATC Phraseology for the Provision of Wind Shear Alert Information
That,
a) Table 12.3.1.7 of Doc 4444 be extended to include the wind shear phraseology as follows:
12.3.1.7 METEOROLOGICAL CONDITIONS / a) …
…
… for alerting approach or departure aircraft to microburst / p) [CAUTION] [RUNWAY (number)] MICROBURST [ALERT] [MINUS (or PLUS)] [(number) KNOTS (or KILOMETRES PER HOUR)] [LOSS (or GAIN)] [(number) MILE] [ON] [FINAL] [APPROACH (or DEPATURE)] [RUNWAY]
Note 1.Either [CAUTION] or [ALERT] should be used.

Note 2. Either
[(number) MILE][FINAL (or DEPARTURE)][ON RUNWAY]
or
[ON][FINAL APPROACH (or DEPARTURE)][RUNWAY]
should be used
Note3.Either [MINUS (or PLUS)] or [LOSS (or GAIN)] should be used for the sign of the microburst magnitude.
… for alerting approach or departure aircraft to significant wind shear / q) [CAUTION] [RUNWAY (number)] WIND SHEAR [ALERT] [MINUS (or PLUS)] (number) KNOTS (or KILOMETRES PER HOUR) [LOSS (or GAIN)] [FORECAST (or REPORTED)] [(number) MILE] [ON] [FINAL] [APPROACH (or DEPARTURE)] [RUNWAY]
Note 1.Either [CAUTION] or [ALERT] should be used.
Note 2. Either
[(number) MILE][FINAL (or DEPARTURE)][ON RUNWAY]
or
[ON][FINAL APPROACH (or DEPARTURE)][RUNWAY]
should be used
Note 3.Either [MINUS (or PLUS)] or [LOSS (or GAIN)] should be used for the sign of the wind shear magnitude.
Note 4. [FORECAST] could be used, as an option, for a wind shear alert generated by a forecast algorithm rather than detection based on ground-based, wind shear detection or remote-sensing equipment.
Note 5. [REPORTED] could be used, as an option, for a wind shear alert corroborated by pilot report(s). If this reported wind shear alert happens to be generated by a forecast algorithm (see Note 4 above), [FORECAST] should be omitted in this case.

b)Para. 11.4.3.2.3 of Doc 4444 be amended to include specific reference to wind shear.

4. ACTION BY THE metwsg

4.1The METWSG is invited to:

a) note the information in this paper; and

b) decide on the draft action proposed for the group’s consideration.

— END —