PDA

View Full Version : Winds on Final


FlightPathOBN
25th Aug 2012, 17:44
One of our systems measures the wind column at 1500m and 2500m from threshold. It gives the wind speed and direction about every 5m in elevation, so one can see the wind shift.
There have been many questions regarding configuration settings regrading winds on final, so I have a general question.

If we are measuring the winds, and it shows a shift at say 400 feet, as an example from a tailwind to a crosswind, or headwind, what would be the best way to advise?

I am looking for an easy way for the crew to be advised of that condition and be able to set final config appropriately...

Thanks for any and all advice..

Tu.114
25th Aug 2012, 17:50
At VIE and other Austrian airports, such an observation is reported on the ATIS. It will show in addition to the threshold wind reading e. g. "Wind at 1000 above aerodrome level 290/25".

This is rather useful information to have for the approach.

FlightPathOBN
25th Aug 2012, 17:54
Thanks for such a quick response, I had just thought that I needed to be more specific, I was meaning the straight to the point verbiage, noting specific winds before/after the shift with altitude...

Thanks

I can certainly see the need for specifc wind data, especially at the critical 300-500 foot HAT...to avoid overspeed or stall

A4
25th Aug 2012, 18:27
It depends on the Operators SOP's as well. My company has a preferred landing CONFIG of Flap3 (subject to runway length) but it is up to the operating crew to choose.

One of the main factors is wind component on final approach - not just the surface wind. If there is a tailwind on the approach then it's flap full usually as the aircraft deceleration is too slow whilst trying to comply with ATC speed requests (160 to 4d). Likewise a crosswind, straight across, on the approach can also compromise deceleration to the point where it's easier (from a stability point of view) to just elect to use flap full.

It is a requirement that we must be in the landing configuration by 1000' agl and we must be stable at 500'.

When we brief the approach we will state the proposed config - but can elect to modify it subject to conditions. If I'm honest, I would treat any reports of a wind shift in my favour around 500' with caution. If there's a chance I'm going to be unstable I'll just elect to go flap full - I may burn a little extra fuel but it'll be a damn sight less than a go-around!

The way VIE does it sounds simple and will give the crew an early heads up - particularly as we listen to the ATIS prior to briefing. The more info the better!

FlightPathOBN
25th Aug 2012, 18:58
Thanks...I have noticed at a particular installation, that especially at night, the temp inversion causes the winds the shift as it rises, to about 500 feet or more it can be 90 to 180 degrees shift.
Given one must be stabilized by 500, so the wind shift below 500 is very critical, that is really my question, how would be the best way to advise, with ATC, ATIS, or ACARS..and would it be of value to go through the process for me to broadcast through these systems...

just to add, for severe cases, I am looking at broadcasting the windshear alert as well...

A4
25th Aug 2012, 19:22
ATIS gives "planning/long term" info which improves our situational awareness as to what might happen. Reports from ATC by recent measurement and/or experience of recently landed aircraft (which we often get in windshear conditions) allow us to finesse the decision.

Whilst we (I) like to operate as efficiently and safely as I can, there comes a point when margins between being efficient and ensuring I'm stable dictate that I will take the "easier" option and just go flap full. However having additional info available would be of great benefit. Perhaps we could get it in Spain when "wind calm, clear to land" usually translates to a 15 knot tailwind in short final and about 5-10 tail during touchdown....:hmm:

FlightPathOBN
25th Aug 2012, 21:50
A4,

This data should be much more finite...dont want to have to rely on ATC, but more of a broadcast ....


Is anyone running FIS-B or UAT ADSB uplink?

GlueBall
26th Aug 2012, 09:03
Given one must be stabilized by 500, so the wind shift below 500 is very critical, that is really my question, how would be the best way to advise, with ATC, ATIS, or ACARS

We don't listen to ATIS nor dabble with ACARS @ 500 feet with just 20+ seconds to touchdown. :ooh:

A4
26th Aug 2012, 09:19
It boils down to a time and workload management issue. If this info were to be broadcast then it would have to come through visually i.e. uplinked in someway. In the later stages of an approach (<5,000') it really is unwise to have someone off freq getting the latest short final spot winds. If it were to come from ATC, it would need to be a defined format on first contact with tower - which will increase RT workload on the controller. We typically contact tower at about 6-7 miles which is 2000'agl so any info received and final landing flap decision would have to be made in the next 500'. Not impossible but not ideal......

I think this info is best broadcast early (ATIS) and if there is a wind shift above a certain threshold which is likely to have a noticeable affect on the approach in short final that could be broadcast by tower - la Windshear conditions.

A4

FlightPathOBN
26th Aug 2012, 18:43
Thanks, that is certainly doable....

just broadcast the winds over ATIC or ACARS, typically at 1000 feet and 500 feet for configuration purposes...

then if there is a windshear, broadcast the speed and direction changes with altitude so one has time to decide on config....

the system updates every 10 seconds or so, that giving enough time to change the message....and with the locations of the system, enough time to react, if things get real ugly with something like a microburst, for a GA...

FullWings
26th Aug 2012, 19:24
HKG has a fairly complex wind reporting system and tacks forecasts/reports onto the end of the ATIS. There's also a "terrain-induced microburst" warning...

At the end of the day, if the surface wind is markedly different from that aloft, you know you're going to have to traverse a gradient. The type I fly can use full speedbrake with land flap, so a detailed vector wind slice is interesting information but not really required. If we've used all the tools in the box and the approach still isn't stable, then we'll go around. Not hard to figure that one.

The most extreme examples I've come across have been in hot countries at night with calm at the surface and jet-stream speed winds at 500-1,000', plus when you're very close to a frontal boundary with a shallow layer of cold air under warm. In both cases it was fairly obvious what was going on.

I agree with previous posters that 500' and 1,000' winds are useful but any more than that is information overload. With whatever's there you're going to have to react to it based on what is actually happening that instant, not what's on the forecast or ten seconds ago. Also, we're pretty limited on what we can do - it's not a normal SOP to come in at Vref minus 20 just because there is an alleged gain of 25kts on short final...

FlightPathOBN
26th Aug 2012, 23:15
FW, thanks..

I know that this level of wind data, will be much more useful in the automated systems in the near or near future, rather than listening to a message, its just uploaded for use.
There are a few premium FMC solutions which can use the data real time.

Yes, I was looking at DOH, with a consistent issue with over-runs and GA due to the significant windshear at 500 feet.

That is likely an issue with daytime/nighttime temp extremes, near water, and mountainous airports as well.

This wind data is part of the wake turbulence system, that I feel can have immediate side benefits for approach configuration.

Tu.114
27th Aug 2012, 05:27
Forgive me, but I do have some slight doubts here.

As has been mentioned, the stabilization gates for the approach are between 1000 and 500 AAL, so the decision on flap setting and approach speeds (and prop RPM on a turboprop) will be made way before this. If something untoward happens close to or below those altitudes, it will be a go around instead of a reselection of flap or other setting - and usually, a nasty gust, a windshear or whatever else will be noticed much quicker by the crew itself than it can be sniffed by any system, relayed to tower and then broadcast by whatever means.

So I think a system that monitors such small-scale weather definitely has its merits and is desirable to have. But instead of flooding crews with information on short-term changes, simply giving them a heads-up on the observance or possibility of low-level windshears or the like before they even decide for the approach and their required type-dependent settings seems useful enough.