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Young_Turk
18th Jul 2007, 04:30
the 737 NG i fly has a tailwind limitation of max 15 kts.... but does this include gusting winds as well?? if the winds are "dead tail" 14 knots and gusting dead tail 20 knots.... is the limitation breached?
if Boeing had so explicitly mentioned the gust factor in head winds... how about boeing coming out clean on tailwind gust factors?
your comments..
thanx

Rainboe
18th Jul 2007, 11:27
You must not even think of landing with even a puff of wind above 15 kts tailwind. There is no gust factor- any mention of anything above 15 kts means you are trying to land on the wrong runway! The gust factor is not even mentioned for tailwinds because there is none. Is that clear enough?

fireflybob
18th Jul 2007, 11:36
Absolutely correct, Rainboe!
Also remember that tailwinds are factored, for performance calculations, by 150 % !

BelArgUSA
18th Jul 2007, 12:56
Hola Young Turk /
xxx
If your airline permits landings with 15 kts tailwinds, I suggest that your flight operations management is seriously incompetent. With my airline, while the aircraft AOM (chapter 23 for the 747, I think it is the same chapter number in the 737) might show 15 kts on performance graphs, our GOM policies, limit any tailwind to 10 kts.
xxx
And despite that 10 kts rule, our crews have been instructed to refuse any takeoff or landing on runways when the wind component would exceed 5 kts!
xxx
:)
Happy contrails

Centaurus
18th Jul 2007, 13:14
The problem with any tailwind component is that invariably the tailwind is stronger with altitude which means you are left with a higher than expected ground speed over the threshold.

IRRenewal
18th Jul 2007, 13:42
Centaurus,

'Surface wind' is measured at 30 feet. Don't think it's going to make a lot of difference to the 50 feet wind, which should be your threshold crossing height. I'd be more concerned about the 1000-2000 feet wind, which could well be a 30 kts tailwind. This might make it hard to establish a stabilized approach by whatever your company's requirements are.

BelArgUSA,

My company allows 15 kts tail wind landings (B738) at a limited number of destinations (where there are no instrument approaches to the opposite runway for instance). This may be combined with additional restriction as to landing weight etc., but is always subject to detailed performance analysis to ensure the safety of the flight.

To me this sounds like a much more competent approach to the issue than an outright 5 kts limit.

If I need to choose between a circling approach at night with wx close to circling limits or a straight in ILS with 14 kts tailwind then, subject to landing performance considerations, I know what I prefer.

safetypee
18th Jul 2007, 13:49
A pedantic point f-f bob, but I understand that it is the performance that is factored not the wind. Often many pilots fall into similar traps where they assume that ‘factoring’ takes care of all eventualities (IRR – “detailed performance analysis to ensure the safety of the flight”). Of particular interest would be the accuracy of wind reports; see 2001 ‘Safety aspects of tailwind operations’ (www.nlr-atsi.com/publications.php) and the other reports relating to wind.
I assume that factored performance does not account for errors in wind measurement, thus the application of additional safety margins is another of those items which crews are expected to be aware of and use ‘airmanship’ to decide when to apply them.

My advice for those using factored information is to consider that the risk of you making an error is proportional to the applied factor, thus in a tailwind you are 150% 'more likely' to get something wrong.

Young_Turk
18th Jul 2007, 17:28
Well thanx a lot guys for the input....
this backs my decision to divert from an island airfield in the middle of the bay of bengal (india)... winds were as reported earlier but a few "brave" pilots did land ... (a certain low cost carrier with a 320 full of backpackers i guess ) ...but i decided to come back to calcutta with those winds... not with a doubt on my capability with landing a 738 with 65 tonnes on LW on a 9000 foot runway... just cuz... my books say no ... !!

Rainboe
18th Jul 2007, 20:24
Wise decision! But why can't you land the other way? Most types specify a 10 kt tailwind limit, period. On a long runway maybe it wouldn't be a problem, but operating so clearly and unambiguously outside the Flying Manual restrictions, anything goes wrong, blown brakes/tyres/pod scrape whatever, you will be hung, drawn and quartered. Just not worth the risk.

john_tullamarine
19th Jul 2007, 02:05
Some thoughts ..

(a) performance certification work is done for steady wind

(b) an individual airline's level of conservatism, with respect to the certification limits, is a matter for that airline's risk management policies, etc.

(c) Surface wind is measured at 30 feet. because the observed boundary layer near the ground is not dissimilar to that along the wing in that there is a significant variation near the ground ... the certification relationship has been discussed previously (http://www.pprune.org/forums/showthread.php?s=&threadid=10456). The wind at 2000 ft is irrelevant .. it is the variation at low level which bites ...

(d) I understand that it is the performance that is factored not the wind .. not quite. The AFM charts will apply a 0.50 factor for headwinds and 1.50 for tailwinds. This is done by scaling the chart for the reported wind .. but using half that value for headwinds (and 1.5 for tailwinds) in the chart. One can tell if the chart is factored by looking at the wind component grid .. if there is a noticeably sharp kink in the carpet lines at zero wind (where the factors change) then the wind is factored. This will vary from Standard to Standard implementation .. generally takeoff charts will be factored but landing may not be .. in which case the pilot has to apply whatever operational standard requirement is relevant to the jurisdiction.

FIRESYSOK
19th Jul 2007, 02:40
So the gust value for any wind must be considered, correct? I recently overheard a dispatcher and pilot arguing this very thing. The pilot contended that the gust was exceeding company crosswind limitation, and the dispatcher says we consider the "steady" value only. Now since I can't find any reference in company material, is there regulatory guidance or precedent on the issue? Thanks.

Bungfai
19th Jul 2007, 02:54
What about max cross wind? My company is trying to raise max crosswind limit from 30 kt to 40 kt on B777. :rolleyes:

john_tullamarine
19th Jul 2007, 04:26
(a) So the gust value for any wind must be considered, correct ?

I don't know that you will be able to pin down a regulatory reference as easily as you might desire. However, consider what your response might be at the enquiry when you are asked why you decided to launch or land with the reported wind at XYZ ?

Consider, also, that the forecast gust is a statistical animal and the expected maximum gust levels are somewhat higher ...... me, I'd tread a bit warily in gusty, limiting conditions .. generally one can come back and try again after diverting. At the end of the day there is no room for heroics in the absence of pressing (non-commercial and real) need ..

(b) What about max cross wind?

Not a major problem philosophically. I have been involved in just this process in the past and my present fleet aircraft has a low priority project in train to do just this ...

Consider that you will need competent engineering assessment as to whether there may be any structural considerations to address. Then, it's a matter of finding suitable conditions for a test program utilising appropriate TP personnel in association with the Regulator .... If all goes well the end result is a mini recertification of your birds to reflect a higher demonstrated value or limit, according to the flavour which the particular Regulator adopts ...

Young_Turk
19th Jul 2007, 16:12
Thanks for the amazing replys.... i dare say some of the discussions were very enlightening indeed !! as for my decision to return and not try the reciprocal approach... its cuz VOPB doesnt HAVE an opposite side approach. Its an island airfield where halfway down the runway there is an upslope and where the runway ends...the terrain continues into this 300 feet hill !! so its a uniderectional runway. rwy 04 for approach... and rwy 22 for takeoffs.
cheers....

Centaurus
20th Jul 2007, 01:10
'Surface wind' is measured at 30 feet. Don't think it's going to make a lot of difference to the 50 feet wind, which should be your threshold crossing height. I'd be more concerned about the 1000-2000 feet wind, which could well be a 30 kts tailwind. This might make it hard to establish a stabilized approach by whatever your company's requirements are.


Yes - that is true. My wording wasn't very good. I meant precisely what you have described above.

jeremydewever
20th Jul 2007, 05:18
is that trew we can have a tail strike in the airbus A319 ?