ICAO wind?

[BSD]

On the approachto LGW this morning, in all the fun and games, the tower were giving 2 winds, broadly similar, but the second, and slightly stronger I think was prefixed the ICAO wind.

Forgive me if I've missed something, but what's that all about?

New one on me, and I' love to learn what it is all about.

BSD.

[Spitoon]

Sounds all very non-standard but I suspect it comes down to the time over which the wind velocity was averaged.

The normal, ICAO-standard wind that you will be passed by ATC at an airport is a rolling average over the previous 2 minutes (as a point of interest for anyone not familiar with this stuff, the value that you see on a METAR is averaged over the 10 minutes prior to the time of observation). Most airports are fitted with equipment that will give an 'instantaneous' w/v value - it's actually still an averaged value but, if I recall correctly, over 5 seconds.

Some pilots prefer the instantaneous value in challenging conditions and it is always available on request. The correct phraseology (in the UK) when an instantaneous wind is passed is 'Runway XX cleared to land instant surface wind XXX degrees XX knots'.

Bear in mind that the instaneous wind report may not include information about the gustiness of the wind, either because the sensing equipment filters it out or the controller has not spotted the recent maximum and minimum values.

[Gonzo]

BSD, are you sure you heard 'ICAO' and not 'Instant'?

Unless KK's local procedures say otherwise, in the UK 'Surface wind' is the two minute average, and any other wind passed (excuse the pun) must be prefixed, i.e. 'Instant surface wind'

It's interesting to note that, in my experience, many flight crews don't know that we usually read out the two minute average.

[alf5071h]

Any help? See Chapter 3 … measurement of wind conditions.

‘Safety aspects of aircraft operations in crosswind.’ (www.nlr-atsi.com/downloads/NLR-TP-2001-217.pdf)

[BSD]

Thanks all for your replies, and the various references.

Gonzo, yes I´m pretty sure that ICAO was the prefix LGW tower were using. Mind you, I did rather have my hands full of 767 at the time!

Gone skiing at the moment. I´ll read through everything properly when I get home, but it does bring up another ATC wind question I´ve been puzzling over.

Namely, the gust quotient. If my research doesn´t resolve, I´ll be back.

Cheers all.

BSD.