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Nick Dobda

what to do with wind info just prior to takeoff

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When getting cleared for takeoff and landing, ATC recites the latest wind info. What do we do with this info? Is it just a mental note? Are we supposed to enter that into the FMC (takeoff)? Surely we don't have time to recalculate the thrust settings... is there some range the pilot is looking for to stay within to ensure the takeoff setting are still valid? What if the winds change enough to warrant recalculating takeoff settings? Does he pull the plane aside and tell ATC to hold up while I reconfigure? Does that ever happen?


Nick Dobda

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Is it just a mental note?

 

Yep.

 

The rest of the questions are overthinking it, really. If the wind changed that drastically, you might want to call your meteorology/planning department to have a discussion about forecasting and quality.


Kyle Rodgers

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Thanks, I wasn't sure I was kind of disregarding the info trusting the weather info ASN told me and was used in takeoff configuration was accurate (especially in a sim considering ASN is generating the weather). For landing, I was pretty sure it was FYI cause there's nothing to program and you react to whatever comes your way on the approach with control inputs. 


Nick Dobda

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For landing, I was pretty sure it was FYI cause there's nothing to program and you react to whatever comes your way on the approach with control inputs. 

 

Correct. Just as with takeoff, it's just a cursory check to give you the latest wind that you will have to adjust to.*

 

Not everything needs to go into the FMC. It's possible to fly an entire flight in the 737 and ignore the thing entirely. It certainly makes life a lot easier, but remember that it's a tool to assist you and not a tool to bind you.

 

 

 

*Side note: If a departure procedure says "fly runway heading," then you should not adjust your heading to track down the extended centerline. If the runway course is 191, then you should put your aircraft's nose on 191. If everyone is flying heading 191 on departure, they will all drift at about the same rate, relieving all of the crews of having to worry about wind correction.


Kyle Rodgers

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but remember that it's a tool to assist you and not a tool to bind you.

 

Yeah, I get that. Takeoffs though its cool to use up all the runway available instead of gunning it on takeoff. Miscalculating on the takeoff mode and derates could obviously lead to some problems. Like you said though for weather to change enough to become a problem between the gate and the runway is extreme and unlikely.


Nick Dobda

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It's a bit more than a mental note in so far as if you have company crosswind/tailwind limits and the tower reported wind was outside of those then you would be rather brave to disregard it.

 

It's slightly different in the sim because the only weather info we have is the METAR, which is (IIRC) the 10-minute average wind just prior to the METAR being published. The wind you get from the tower, on the other hand, in real life is much more current -- again IIRC usually more like a rolling 2-minute average or if requested the 'instant' wind direct from the anemometer is also available. Both of these values could be significantly different to the METAR in changeable conditions (especially if it's been a while since it was published).

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Simon Kelsey

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The wind you get from the tower, on the other hand, in real life is much more current -- again IIRC usually more like a rolling 2-minute average or if requested the 'instant' wind direct from the anemometer is also available.

 

Those are the two most common. I know some of the older towers here in the States read right off of the anemometer (what the 7110 refers to as the "direct readout dial") since that's just about all they have, but the automated weather system information display is also an option (similar to what many FBOs have on display somewhere in the building). The additional option allowed by the 7110 is a reading off of the windshear detection system.

 

All are much better than what you get in the sim, as you noted.


Kyle Rodgers

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You could enter the wind info on the 2nd page of the takeoff page in the fmc. But, yes as Kyle stated, it's a mental note so you know on the takeoff roll how much to correct for wind - David Lee

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And... don't forget, the meteo man always says the TRUE ( wind )....

 

Just as winds reported in METAR, SIGMET, TAF are TRUE.

 

We never lie!

 

Since within the USA it can var as much as 25W and 20E at some airfields, this can really be significant, and you'd better make your mental conversion :-)


I will believe in MFS the day I can Uninstall it !

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And... don't forget, the meteo man always says the TRUE ( wind )....
 
Just as winds reported in METAR, SIGMET, TAF are TRUE.

 

But not when given by the tower (which is magnetic)!

 

Generally speaking -- if it's spoken it's magnetic, if it's written it's true.


Simon Kelsey

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The meteo man isn't at the tower.... :-)  but we're not far, usually...


I will believe in MFS the day I can Uninstall it !

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Yeah, it's advisory but a good cross check on actual conditions as you start your roll. For instance, if your takeoff data is just predicated on no headwind, but the wind direction shifts a bit and the reported takeoff wind now contains a small tailwind component, your takeoff data is now technically invalid. Are you going to decline the takeoff clearance and taxi clear to get new data? On a 12000ft runway, at sea level, with a 2 kt tailwind? Well... do you have a fed in the jumpseat? :-D

 

On the other hand, on a 5,000ft, wet runway that ends in saltwater? Yeah maybe!


Andrew Crowley

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Since within the USA it can var as much as 25W and 20E at some airfields, this can really be significant, and you'd better make your mental conversion :-)

 

Tower controllers apply the correction here in the States.


Kyle Rodgers

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You might also be limited by the winds. If you're really pushing the limits, you might be looking for a minimum headwind or maximum tailwind. There could also be crosswind limits based on less than good braking action.

 

Nothing to do with the FMC, really.


Matt Cee

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Nice little cross check.

ie:
1: Prepare for your departure, get ATIS and clearances and stuff. Check the wind with topcat etc for V speed calculations

"Hey look, runway 19, wind 180 at 10 knots"

2: Tower tells you the actual winds just before takeoff

"ABC123 wind 180 at 15 knots, Runway 19 cleared for takeoff"

"Hmm that didn't match, but it's still fine. Let's takeoff."

 

or

"ABC123 wind 280 at 30 knots gusting 45, Runway 19 cleared for takeoff"

"hmm that REALLY didn't match at all! 280 - 190 = 90. That's all crosswind. aww this sux.

 

or

"ABC123 wind 340 at 30 knots gusting 45, Runway 19 cleared for takeoff"

"hmm that REALLY didn't match at all! 340 - 190 = 250. 240>90. A bunch of that is tailwind. a 30 to 40 knot tailwind is out of limits. We might need to say no to runway 19! Why didn't they give use 01? what's going on? I want no part in this crash waiting for a place to happen! Let's say no, and run our numbers again or double-check if they want to change their runway."


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Trent Hopkinson, 2015 Crewmember of www.mangrove.com.au WorldFlight sim

          Youtube channel www.youtube.com/user/musicalaviator

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