julesmusician
Posts: 378
Joined: Sun Aug 28, 2005 3:25 am

Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 1:40 am

What are the rules on runway inclines and winds? If the runway is inclined and the pilot could take off downhill but there is a strong tail wind is there some kind of balance that pilots work out the advantage of going one way or the other? Is it better to go uphill into a wind or downhill with a tailwind component? I am told that HYDERABAD (HYD) has a substancial incline is such an airport..
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
IFACN
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Joined: Sun Nov 20, 2005 7:14 am

RE: Runways On Inclines Go Downhill Even If Tailwi

Mon Nov 21, 2005 1:58 am

I'm curious about that too.

In Northern Italy, Torino Caselle (LIMF) airport has a pretty inclined rwy and landings/takeoffs are always uphill (rwy 36, 3300 meters).

I never saw or heard about any plane land or takeoff on rwy 18.

What's worth noting is that rwy 36 is in the direction of the nearby hills and taking off from Caselle requires an immediate hard turn to right
a) to avoid the highest hills and mountains
b) to reduce noise levels on the nearby towns
 
SlamClick
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RE: Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 1:59 am

You do not want to take off downhill if it can be avoided.

In the first place just about all airliners have a type limitation of 2% runway gradient. That is two feet of incline per hundred feet of runway length, or "rise over run" to calculate it. Very few airports in the devleoped world have slopes that exceed this. Aspen Colorado does, and airlines have to get a waiver by "demonstating an equivalent level of safety" in order to operate there. What it really means is that they are severely weight-restricted there. I believe that it is customary to take off downhill because of rising terrain at the uphill end.

Remember that takeoff performance is not all about getting off the ground. It is largely based on safety with an engine failure. Taking off downhill seriously increases stopping distance in the event of a reject. So down slope decreases V1 and we would, if anything, prefer to take off up hill. We just don't want to go wallowing out over rising terrain if we lose an engine.

edit: I answered the above from an airline, or multiengine point of view. In singles, and particularly STOL ops, taking off down a hill would probably be better in most cases. Most extreme runway I ever used regularly was about 1200' long and sloped a full 200' in that distance. I landed up the hill and took off down the hill. If there was any wind at all I did not go in there. The first plane to use the strip crashed on takeoff. They took a Cat back and knocked down a couple of humps and I was the second plane to use it. (Cessna 206 with a STOL kit) The good news was, it was not necessary that you be able to climb because the canyon sloped away sharply from the bottom end of the strip. I forgot to mention that it was roughly seven thousand feet above sea level.

[Edited 2005-11-20 18:02:43]

[Edited 2005-11-20 18:05:59]
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
julesmusician
Posts: 378
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RE: Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 2:27 am

Interesting - I can't imagine a fully loaded 747 - 400 with max take off weight heading uphill with a tailwind but I am sure it happens, well I suppose you could have to take off some weight in that case. How does all the relevant V speeds calculate the fact that the runway has an incline or do they not need to take that into account? Does going uphill change how quick you want to get off the ground?
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
IFACN
Posts: 149
Joined: Sun Nov 20, 2005 7:14 am

RE: Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 2:34 am

Thanks, SlamClick, you made it really clear.

At Torino Caselle airport (both domestic and European routes, so it's an airline/multiengine issue rather than a single/STOL) the slope is about 1.5%.

Speaking of engine failures, in 1997 (or '96) an Antonov jet trying to land at Caselle had some serious problem and called for a go-around, but failed to climb and smashed on the hills 2km north of rwy 36, killing the crew and other four on the ground.

After this, the take-off or go-around procedure was changed to make the hard turn to right.
 
jspitfire
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RE: Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 4:54 am

Powell River airport, which isn't too far from Vancouver, has a 2% slope. There is a picture in the terminal of a Hercules taking off downhill with about a 15 kt tailwind. The runway is only 3600' long, but I don't understand why he wouldn't take off up hill with a headwind...From The explanations given here, that sounds like the better course of action.

Jason
 
SlamClick
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RE: Runways On Inclines Go Downhill Even If Tailwind?

Mon Nov 21, 2005 5:05 am

Quoting Jspitfire (Reply 5):
From The explanations given here, that sounds like the better course of action.

What is best is not always intuitive. That is why the bigger airlines employ perfomance engineers who run a small department that does this stuff, runway by runway through their entire route structure. There are also freelance engineers who sell airport analysis information. Some airlines have it in laptops for their crews, some send it via ACARS and some still have a big three-ring binder in each airplane. And when I say runway-by-runway I mean that 09L and 27R are two different runways even though they are the same strip of concrete.
Happiness is not seeing another trite Ste. Maarten photo all week long.

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