LU9092
Topic Author
Posts: 107
Joined: Thu Oct 18, 2007 2:09 am

Headwinds On Approach And Landing

Sun Oct 28, 2012 7:59 pm

I know aircraft have a certified max crosswind component for landings and takeoff, but what about headwinds? My girlfriend should be departing RDU for JFK in a half hour or so, and another friend is enroute to LGA from DEN, and I'd been keeping an eye on whether winds had gotten strong enough to constrain LGA and JFK to using their 4's. Winds are forecast to be right down the centerlines the rest of the afternoon into this evening, which made me wonder how much headwind is too much? Are aircraft certified for a certain max, or is it something an airline would define in their SOP? I then wondered if the is a max certified crosswind for taxiing. I imagine a 70 Kt gust could swing the tail of a taxiing airliner.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Headwinds On Approach And Landing

Sun Oct 28, 2012 8:22 pm

Quoting LU9092 (Thread starter):
I know aircraft have a certified max crosswind component for landings and takeoff

No, they don't. They usually have a maximum *demonstrated*, which the airlines then use as the basis for their SOP's (usually with some reduction), but they don't have a maximum certified.

Quoting LU9092 (Thread starter):
but what about headwinds?

Unless they're so high that flight operations are suspended, they're not really a problem.

Quoting LU9092 (Thread starter):
which made me wonder how much headwind is too much?

Well, if the wind was above Vmcg then you couldn't takeoff but Vmcg is usually 100+ knots and that's well into hurricane territory, by which time flight operations would have long since ceased.

Quoting LU9092 (Thread starter):
Are aircraft certified for a certain max, or is it something an airline would define in their SOP?

The latter.

Quoting LU9092 (Thread starter):
I then wondered if the is a max certified crosswind for taxiing.

Not explicitly. Above Vmcg you can't guarantee that the rudder will provide enough sideforce to keep you straight but that assumes that you don't have any nosewheel steering. The practical limit is somewhat above Vmcg but, as noted earlier, you'd have suspended flight operations long before then.

Quoting LU9092 (Thread starter):
I imagine a 70 Kt gust could swing the tail of a taxiing airliner.

If the surface was slick, that is a possibility. The weathervane tendency would certainly be strong. You could battle it with differential thrust but, under those conditions, I'd call of the flight if I were PIC.

Tom.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: Headwinds On Approach And Landing

Sun Oct 28, 2012 8:58 pm

Quoting tdscanuck (Reply 1):

If the surface was slick, that is a possibility. The weathervane tendency would certainly be strong. You could battle it with differential thrust but, under those conditions, I'd call of the flight if I were PIC.

As a matter of fact, there are some limitations one could very well keep in mind : Wind limit for door operations and slide deployment limit . They vary from a model to another but ballpark figures would be 65 and 30 kt .

On the other hand, there are headwind component limits for autopilot Cat II and III approach, land and rollout : around 30 kt.
Contrail designer
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Headwinds On Approach And Landing

Sun Oct 28, 2012 11:22 pm

Quoting Pihero (Reply 2):
On the other hand, there are headwind component limits for autopilot Cat II and III approach, land and rollout : around 30 kt.

Absolutely true. As the headwind increases the flight path in the air has to change to keep the inertial flight path on the approach, which plays directly into how a bunch of the control laws inside the autopilot work. They don't have infinite envelopes so you have to go over to hand-flying at some point. In all likelyhood, the autopilot may be capable of more but it was just never demonstrated for more. When chasing winds for certification, you have to take what you can get.

Tom.
 
LU9092
Topic Author
Posts: 107
Joined: Thu Oct 18, 2007 2:09 am

RE: Headwinds On Approach And Landing

Mon Oct 29, 2012 3:18 pm

I appreciate the info!
 
musang
Posts: 788
Joined: Sun Apr 08, 2001 4:11 am

RE: Headwinds On Approach And Landing

Mon Oct 29, 2012 4:06 pm

And the 737 classic has a limitation of 65 knots wind for ground operations which, due to the need to taxi to the runway, would effectively become a take-off headwind limit.

Regards - musang
 
OldAeroGuy
Posts: 3318
Joined: Sun Dec 05, 2004 6:50 am

RE: Headwinds On Approach And Landing

Tue Oct 30, 2012 3:38 pm

Quoting tdscanuck (Reply 1):
Above Vmcg you can't guarantee that the rudder will provide enough sideforce to keep you straight but that assumes that you don't have any nosewheel steering.

You mean below Vmcg. if the airplane is above Vmcg, the rudder can be used to maintain directional control if an engine fails and is able to continue the takeoff.

Below Vmcg, an engine failure means the good engine must be cut and the takeoff must be be aborted.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Headwinds On Approach And Landing

Wed Oct 31, 2012 1:28 am

Quoting OldAeroGuy (Reply 6):
You mean below Vmcg.

Yes. Yes I do.

Tom.

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