Magcheck
Topic Author
Posts: 16
Joined: Tue Aug 17, 2010 2:11 am

Tailwind Landings DCA

Wed Mar 23, 2011 1:03 am

Listening to ATC tonight and was surprised to hear a few CRJ's landing on 33 (5,204 x 150). Wind 10009. Even for small jets I thought this was strange.

1.) Is this unusual?
2.) Is there a tailwind "limit" per se for certain aircraft/runways/conditions or do they just crunch the numbers and go with ground roll figures?
3.) Even if the math works out, why not go conservative and take Runway 1?

Thanks!
 
loggat
Posts: 426
Joined: Sat Feb 12, 2000 11:34 am

RE: Tailwind Landings DCA

Wed Mar 23, 2011 2:39 am

1. Not unusual to use 33. That wind condition makes it less likely though.
2. Tailwind limit for many airliners is 10kts, regardless of runway length. A tailwind requires a higher rate of descent so the possibility of harder landings. It does not depend on specific runway configurations, you just have to crunch the landing performance numbers and add the pilot comfort factor and see how the numbers line up. If the data shows you need 3000' then you are only using 60 percent of the runway. For my aircraft (E170/E190) I wil generally land at flaps 5 on runway 1, and flaps full on runway 33 so I end up using the same percentage of the available runway.
3. Although it is more conservative to take runway 1, there are still different levels of conservatism. As long as runway 33 is deemed to be almost as safe as 1, then sometimes it is used for a shorter taxi and to assist the tower in able to get a higher departure rate.
There are 3 types of people in this world, those that can count, and those that can't.
 
goboeing
Posts: 2428
Joined: Mon Jun 05, 2000 5:31 am

RE: Tailwind Landings DCA

Wed Mar 23, 2011 2:47 am

Quoting Magcheck (Thread starter):

1.) Is this unusual?

Not really, but the runway is probably about the shortest you'd want it to be with a tailwind.

Quoting Magcheck (Thread starter):
2.) Is there a tailwind "limit" per se for certain aircraft/runways/conditions or do they just crunch the numbers and go with ground roll figures?

Each aircraft has a max tailwind component limitation. For the two jets I'm most familiar with, the EMB-135/145 and the EMB-170/175, it's 10 knots under normal conditions.

That's component though. In this instance, my rough mental math estimates the component would be about 6 knots.

As for the number crunching, there is a certain distance that is to be added for each knot of tailwind component if it gets that close to the actual runway length.

I can't recall off the top of my head what they are because I haven't looked them up in quite some time. To give you an idea, for the E-175 with a normal amount of landing fuel, and say 50-60 pax with their bags, we'll usually show a demonstrated stopping distance of 2200-2500 feet and minimum required of 3500ish for flaps full which we'd probably use for runway 33. So, a 6 knot tailwind component would probably not necessitate adding 2000 feet to what we need.

Quoting Magcheck (Thread starter):
3.) Even if the math works out, why not go conservative and take Runway 1?

It is always an option. It is nice to take the other if able to help ATC but if you can't do it then you can't do it.

It is a bit strange that some of nation's airports are based on not only VFR weather all day long but also ATC pulling every string to create gaps to work more planes in.

Visual 1 circle 33 is fun so I'd do it every time as long as it's safe.  
 
1010101
Posts: 9
Joined: Tue Nov 14, 2006 12:13 pm

RE: Tailwind Landings DCA

Wed Apr 06, 2011 12:27 pm

Quoting loggat (Reply 1):
For my aircraft (E170/E190) I will generally land at flaps 5 on runway 1, and flaps full on runway 33 so I end up using the same percentage of the available runway.

I am curious why you wouldn't use full flaps for all landings. Is it something particular to your aircraft type?
 
ajd1992
Posts: 2390
Joined: Mon Jul 24, 2006 7:11 am

RE: Tailwind Landings DCA

Wed Apr 06, 2011 4:53 pm

Quoting 1010101 (Reply 3):
I am curious why you wouldn't use full flaps for all landings. Is it something particular to your aircraft type?

Sometimes it's a noise issue.

Less flaps = less thrust for the same speed, which = less noise. Does mean a slightly faster landing though.
 
dispatchguy
Posts: 605
Joined: Sun Jan 29, 2006 6:08 am

RE: Tailwind Landings DCA

Wed Apr 06, 2011 5:00 pm

Quoting loggat (Reply 1):
2. Tailwind limit for many airliners is 10kts, regardless of runway length

The standard TW limit is always 10 kts, you can get an operations specification permitting up to 15kt tailwinds for specific aircraft and airports. For example, when I dispatched at Air Wisconsin, we had the 15kt tailwind authorization for one aircraft (N632AW) and at only one airport (Aspen CO).
Nobody screws you better than an airline job!
 
Lemmy
Posts: 243
Joined: Fri Dec 10, 2004 8:40 am

RE: Tailwind Landings DCA

Wed Apr 06, 2011 5:49 pm

Quoting dispatchguy (Reply 5):
we had the 15kt tailwind authorization for one aircraft (N632AW)

Interesting. Why just one airframe and not a whole type? Was there something different about N632AW or was it just easier to get a specification that plane only?
I am a patient boy ...
 
loggat
Posts: 426
Joined: Sat Feb 12, 2000 11:34 am

RE: Tailwind Landings DCA

Wed Apr 06, 2011 7:11 pm

Quoting 1010101 (Reply 3):
I am curious why you wouldn't use full flaps for all landings. Is it something particular to your aircraft type?

There are at least a couple of reasons we don't use full flaps on all of our approaches. The biggest one is fuel conservation. The extra thrust required to overcome the increased drag from full flaps means more fuel burn, which over the course of many flights will add up. The only time we generally use full flaps would be on a short/slick runway.

The difference in Vref speeds for flaps 5 versus flaps full on my plane is about 10 kts. At our general landing weights, that is the difference between 120kts and 130kts. When you have ample runway for landing, then that 10kts doesn't really make a difference, so it goes back to the fuel burn argument.

The last reason is to do with crosswind landings. If there is a pretty stiff crosswind, the aircraft is much easier to control with a lower flap setting. Higher approach speeds from flaps 5 make the ailerons more reactive to the wind.

1. Fuel
2. Ample runway
3. Crosswinds
There are 3 types of people in this world, those that can count, and those that can't.
 
dispatchguy
Posts: 605
Joined: Sun Jan 29, 2006 6:08 am

RE: Tailwind Landings DCA

Fri Apr 08, 2011 11:38 pm

Quoting Lemmy (Reply 6):
Was there something different about N632AW or was it just easier to get a specification that plane only?

It was a lighter airplane - the AFM for the heavier aircraft might not have permitted 15kt tailwind opns, and ASE is a very short runway to begin with...
Nobody screws you better than an airline job!
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Tailwind Landings DCA

Sat Apr 09, 2011 6:01 pm

Quoting dispatchguy (Reply 5):
The standard TW limit is always 10 kts, you can get an operations specification permitting up to 15kt tailwinds for specific aircraft and airports.

Is the 10kt limit coming from the Ops Spec? A 777 AFM gives 15kt limit, and the plane is capable of far more. I've done 30+kts...not particularly good for the brakes though.

Tom.
 
dispatchguy
Posts: 605
Joined: Sun Jan 29, 2006 6:08 am

RE: Tailwind Landings DCA

Sun Apr 10, 2011 5:50 pm

Quoting tdscanuck (Reply 9):
Is the 10kt limit coming from the Ops Spec?

Looking at the FAA website, they actually did away with the OpSpecs paragraph that permitted it - so now, its just the AFM Chapter 1 limitations which apply....

Wow, the FAA doing away with a rule - never saw that coming!
Nobody screws you better than an airline job!
 
MSJYOP28Apilot
Posts: 282
Joined: Tue Jul 21, 2009 2:09 am

RE: Tailwind Landings DCA

Mon Apr 11, 2011 2:29 am

My airline doesnt allow any tailwind on landings on runway 33 at DCA. No wet runways and captain only doing the landing. As a dispatcher, I have to approve them to land on runway 33.

Company tailwind limit though is standard 10 knots with no tailwind for winter airports with contamination on the runways plus for runways that are below a certain standard.
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Tailwind Landings DCA

Fri Apr 15, 2011 8:00 am

Quoting dispatchguy (Reply 8):
and ASE is a very short runway to begin with...

Getting a thousand feet longer in the next few months (work just started).

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