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AM
Topic Author
Posts: 602
Joined: Sat Oct 02, 1999 8:49 am

Requesting Lower Than 250KIAS Climb Speed

Wed Jan 25, 2006 8:27 am

Hi,

I was spotting at MEX last Sunday when AA1596, a 757 (N175AN), just about to take-off on 05L, requested to tower a 220KIAS climb speed. What could be a reason for this?

The only thing that comes to my mind is that the particular crew aboard that airplane decided to climb slower for that particular flight so they would reach a safe altitude faster, given the terrain obstacles in the Mexico City area.

The tower controller instructed them to ask for that with departure, but after take-off, they didn't mention anything about the request.

AM
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xjramper
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RE: Requesting Lower Than 250KIAS Climb Speed

Wed Jan 25, 2006 9:01 am

My guess would be that they were heavy with high humidity and that they could not climb at their filed airspeed and they had to correct that with tower before they took off.

XJR
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wagz
Posts: 483
Joined: Fri Mar 07, 2003 12:48 pm

RE: Requesting Lower Than 250KIAS Climb Speed

Wed Jan 25, 2006 10:28 am

Quoting XJRamper (Reply 1):
My guess would be that they were heavy with high humidity and that they could not climb at their filed airspeed and they had to correct that with tower before they took off.

Had the airplane been heavy, then it would have to climb with a higher airspeed for a given climb rate. The more the weight, the more lift must be produced by the wings, therefore a higher airspeed must be maintained.

But then climbing at a higher airpseed to acheive an equal rate of climb, will produce a lower angle of climb. Angle of climb can become important if there are obstacle clearance concerns.
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Pihero
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RE: Requesting Lower Than 250KIAS Climb Speed

Wed Jan 25, 2006 9:37 pm

The crew of that airplane wanted to maximize their climb gradient for obstacle clearance purposes.
The max gradient should be achieved on a clean configuration around 200 to 230 kts.
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FredT
Posts: 2166
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RE: Requesting Lower Than 250KIAS Climb Speed

Thu Jan 26, 2006 8:02 am

Minimum speeds are not all that common, in my experience. The 250KIAS <FL100 is not one. There are speed restrictions in place for a lot of procedures though, and you'll find speeds below 220KIAS there. My guess is that this was the reason for their request.

Perhaps you can dig up the plates with the departure procedures for that runway?

[Edited 2006-01-26 00:02:32]
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AM
Topic Author
Posts: 602
Joined: Sat Oct 02, 1999 8:49 am

RE: Requesting Lower Than 250KIAS Climb Speed

Thu Jan 26, 2006 9:13 am

Thanks a lot to everyone for your replies.

Quoting FredT (Reply 4):
Perhaps you can dig up the plates with the departure procedures for that runway?

Actually there are only 2 speed restrictions for that particular departure, but none explains the 220 knots request.

The first one is to keep the speed below 200 knots until reaching a fix called VASOS, which is about 5 miles from the departure runway. So from T/O to MEX D5, don't exceed 200. The other restriction is not to exceed 250 knots below 10000' AAL.
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Stoicescu
Posts: 80
Joined: Sun Sep 11, 2005 2:39 pm

RE: Requesting Lower Than 250KIAS Climb Speed

Thu Jan 26, 2006 1:55 pm

Quoting AM (Reply 5):
250 knots below 10000' AAL.


Do you mean 10000 MSL ?

[Edited 2006-01-26 06:01:16]
 
AM
Topic Author
Posts: 602
Joined: Sat Oct 02, 1999 8:49 am

RE: Requesting Lower Than 250KIAS Climb Speed

Thu Jan 26, 2006 3:04 pm

Quoting Stoicescu (Reply 6):
Do you mean 10000 MSL ?

No. Mexico City's airport has a 7316ft elevation, so there wouldn't be much of a case in establishing 10000' MSL as the 250 KIAS limit. The restriction extends all the way up to 10000' AGL above the airport's elevation.

[Edited 2006-01-26 07:05:48]
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Mr.BA
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RE: Requesting Lower Than 250KIAS Climb Speed

Thu Jan 26, 2006 8:10 pm

I've come across situations where an aircraft requested to climb at 210 knots and when asked for reason the pilot said due to weather and bad turbulence. I suppose they would want to climb above the thunderstorm as soon as possible!
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FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Requesting Lower Than 250KIAS Climb Speed

Fri Jan 27, 2006 4:41 am

Quoting AM (Reply 5):
but none explains the 220 knots request.

The first one is to keep the speed below 200 knots until reaching a fix called VASOS, which is about 5 miles from the departure runway. So from T/O to MEX D5, don't exceed 200.

Hmm... there must be a communication error here somewhere. To me, that sounds like a very good reason for the request. If they wanted to climb out at 220, they'd have to request to be allowed to exceed the 200 knot limit on the first 5 miles.
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Grbld
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RE: Requesting Lower Than 250KIAS Climb Speed

Fri Jan 27, 2006 4:47 am

Quoting Wagz (Reply 2):
Had the airplane been heavy, then it would have to climb with a higher airspeed for a given climb rate. The more the weight, the more lift must be produced by the wings, therefore a higher airspeed must be maintained.

Wagz, that is pertinently not true. Economical max rate of climb (altitude per time unit) for a 757 will be around 280 knots, so that's not the issue here. However, when looking at max angle of time (altitude per distance), the slower you go, the better and it may well be at 220 knots or thereabouts on that day. Go any faster and your angle of climb deteriorates.

Grbld
 
BigJimFX
Posts: 301
Joined: Tue Jun 28, 2005 2:25 am

RE: Requesting Lower Than 250KIAS Climb Speed

Fri Jan 27, 2006 12:45 pm

The Pilot may have been trying to prove a point. Here in the DFW Class B airspace they have reduced the max climbout speed to 220 and a lot of the pilots really dont care for it.
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