AMOSSG/3-SN No. 6

16/11/01

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

REPORT OF THE GUST

(Presented by Wil van Dijk )

SUMMARY
The study note describes the impact of the reporting of the gust on the safety of aircraft operations at aerodromes. When applying higher cross and tailwind reference values for the selection of runways, it is proposed to change the reporting of the gust value to support the safety of the aircraft operations.

1.	INTRODUCTION

1.1	The Project Team PT/3 of the EANPG/Aerodrome Operations Group (AOPG) had been tasked with the development of proposals on cross and tailwind criteria for runway selection and the wake turbulence categorisation of aircraft and separation minima. The proposals, when accepted, could lead to an increase of the capacity of the runway(s) and support the safety of the aircraft operations at aerodromes.

1.2	In order to analyse the practice of today by the States, airlines, operators (IATA, IFALPA, IBAC) and aircraft manufacturers, the PT/3 had conducted a questionnaire on aircraft cross/tailwind components/reference values, taking into account the provisions of the Annexes 3, 6, 8 and 14 and the Procedures for Air Navigation Services — Rules of the Air and Air Traffic Services (Doc 4444) and Procedures for Air Navigation Services — Aircraft Operations (Doc 8168). The main questions were related to:

a)	Part 1:

—	the reference cross/tailwind components used for the selection of runways and the criteria for the selection (noise, runway surface conditions, day/night, etc.);

—	the inclusion of the gust in the reference cross/tailwind components;

—	the average time needed to re-organise the traffic for a runway change;

—	the possibility that revised and/or new provisions would be necessary on the subject of reference cross/tailwind components for the selection of the runways in use, when the capacity will become critical.

b)	Part 2:

—	the maximum cross and tailwind components (certified limitations and/or demonstrate values) recommended by the aircraft operators, member airlines or organisation for take-off and landing operations;

—	the inclusion of gusts in these recommended cross/tailwind components;

—	the definition of "gust" used by the aircraft operators, member airlines or organisation.

1.3	Besides of the questionnaire described above, IATA had added separate questions to the questionnaire Part 2. These were:

—	should the gust information be reported as from 5 kt when crosswind becomes marginal?

—	will there be a need for more wind information in different phases of the flight?

—	will there be a need for better accuracy in the wind reporting?

—	should wind components be reported instead of wind direction and speed?

1.4	Beside the outcome of the questionnaire and additional questions, the report of the Rinnooy Kan Committee (report on the Transavia accident at Amsterdam Airport, 24 December 1999) and the studies of the National Aviation and Space Travel Laboratory (NLR) in the Netherlands and MITRE had been taken into account in the further deliberations.

1.5	This study note doesn't deal with all the aspects regarding the cross and tailwind as mentioned in the questionnaire and additional questions, but only on the reporting of the gust value.

2.	DISCUSSION

2.1	The main issues in the discussions on wind reporting have been:

—	cross and tailwind reference values for the runway in use, e.g. 15, 20 or 25 kt resp. 5, 8 or 10 kt;

—	the maximum allowable cross and tailwind value per aircraft type as described in the Aircraft Operational Manuals (AOM);

—	the inclusion of the gust value in the cross and tailwind values mentioned above;

—	the "buffer" between the reported wind, inclusive the gust value, and the reference values of the wind for the runway and/or aircraft which is needed to support safe operations.

2.2	The gust value should be reported accordingly to the Annex 3, para. 4.5.6: "variations from the mean wind speed (gusts) during the past 10 minutes should be reported only, when the variation from the mean speed is 20 km/h (10 kt) or more". However, regarding the reporting of the gust value, as an addition to the average wind, the following examples were presented:

a)	Example 1:

Reported mean crosswind speed	: 16 kt

Gust value (not reported because <10 kt)	: 8 kt

Crosswind reference value of the runway in use (incl. gust)	: 20 kt

Total crosswind speed	: 24 kt

Note 1.— 24 knots is beyond the crosswind reference value of the runway in use.

Note 2.— The crosswind reference values per runway on the aerodrome differs from State to State. The values are 15, 20 or 25 kt for dry runways.

b)	Example 2:

Reported mean crosswind speed	: 24 kt

Gust value (not reported because < 10 kt)	: 9 kt

Crosswind (incl. gust) reference value on landing of

aircraft type, e.g.	: 30 kt

Total crosswind speed	: 33 kt

Note 3.— 33 kt is beyond the allowable crosswind of the aircraft itself as given in the AOM and outside the company limits.

Note 4.— The same kind of examples can be given for the tailwind situation.

Note 5.— There is a buffer of about 50% built into the certification.

2.3	At the end of the discussion, in which the results from the questionnaire, studies and common practice had been taken into account, the final point of view was that: "When higher cross and tailwind reference values will be used for the selection of runways than the actual 15 kt cross- resp. 5 kt tailwind values, then the reporting of the gust should be changed from "10 kt or more" into "5 kt or more." This change would support the safety of the landing and take-off operations at aerodromes."

2.4	On many aerodromes the crosswind reference value today is 15 kt. For this situation the PT/3 doesn't see a strong requirement of changing the gust reporting. However, when the crosswind reference value will be upgraded to the values of 20 or 25 kt, the gust reporting of 5 kt instead of 10 kt will become necessary.

2.5	It has to be noticed that, due to the outcome of the Rinnooy Kan Committee, the reporting of the gust value at the Amsterdam Airport (Schiphol) had been changed already into 5 kt, while using a reference crosswind value including a gust of 20 kt and a tailwind value of 7 kt for the selection of the runway in use. This way of reporting is much appreciated by the pilot community.

2.6	The Rapporteur of PT/3 had presented the result of all the work done so far to the Co-
ordinating Group (COG) of the EANPG at its October meeting in Paris. It was decided to foreword this work to the ICAO/OPS Panel for further studies.

3.	ACTION BY THE GROUP

3.1	The group is invited to:

a)	note the discussion and the resulting requirement for reporting of the gust value of 5kt and more at aerodromes with upgraded wind reference values; and

b)	discuss the insertion of the reporting of the gust value of 5kt in Annex 3, paragraph 4.5.6.

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