# What is the rule of thumb for land/taking-off on a sloped runway?

Skyvector lists the gradient for KMCI as 0.3%. What is the rule of thumb for how large a gradient needs to be before you always take off downhill and always land uphill like they do at Lukla? Assume winds are not a factor.

• actually the reason for only taking off in one direction is terrain. you won't be able to drop to the tarmac after clearing the hill behind it Dec 3, 2014 at 16:32
• A runway with an uphill grade is equivalent to a shorter runway with no grade. You might ask in Physics for the formula.
– rbp
Dec 3, 2014 at 17:01
• @ratchetfreak: Well, VNLK has 12% gradient and that is itself steeper than both descent and climb gradient of most planes, considering the 9 200 ft altitude. Dec 3, 2014 at 20:09
• 12% is 6.875 degrees! wolframalpha.com/input/?i=12%25+in+degrees
– rbp
Dec 5, 2014 at 14:25

Ignoring winds and other factors, it depends on effective runway length, not just runway length. If you have a runway long (really long) enough, you can takeoff/land in either direction.

As mentioned here:

... advantage or disadvantage of a sloped runway is that a 1% runway gradient — an increase or decrease in altitude of 10’ for every 1000’ of runway length — is equivalent to a 10% increase or decrease in effective runway length ...

Example:

Runway length is 1500' with 3% up-slope gradient

• Landing uphill on it will give us an effective runway length of almost 2000’ (1500’ x 1.3 = 1950’).
• Landing downhill on it will give us an effective runway length of just over 1000’ (1500’ x 0.7 = 1050’).

Just for reference, the runway (6: uphill; 24: downhill) at Lukla Airport has 12% gradient and is 1500' long.

Effective Runway Lengths (using the formula above)

 6: 1500' x |(1+1.2)| = 3300'
24: 1500' x |(1-1.2)| =  300'


Hence, hypothetically speaking, if runway 24 is 48,400' long with no wind, A380 can takeoff too.

• Except that you can't land downhill on anything steeper than your descent gradient at all. And you can't take-off uphill from anything steeper than your climb gradient at all either. And in multi-engine you obviously wouldn't attempt to take off uphill steeper than your one engine inoperative climb gradient. Normal descent gradient is 5%, Lukla has 12% (and Courchevel has 18%). Dec 5, 2014 at 19:17
• @JanHudec Good Point. That's why I said hypothetically, not theoretically or practically. Even with no wind, there are many other factors too. I also started the answer with Ignoring winds and other factors.... Dec 5, 2014 at 19:24
• By the way, how do you justify the absolute value? The rule does not say any such thing. The effective length for takeoff on 10% uphill/landing 10% is 0 according to the rule and for steeper gradient it therefore should be negative (so it is minus 300' for landing on VNLK 24) Dec 5, 2014 at 19:40
• @JanHudec I did that because length is a scalar quantity, but I do agree with your example. Dec 5, 2014 at 20:12

I happened to be looking at some takeoff distance charts, so I looked into this. As Tyler says, the answer will depend on your airplane's performance. With good brakes and plenty of runway, a small plane may not care as much as a larger one. The following applies to the PC-12.

I know you said to assume winds are not a factor, but it may help to roughly relate the effects of slope and wind. It turns out that 4% of slope will either help or hurt about the same amount as 10 kt of wind (within about 7%). Both provide around 10% benefit or 25% penalty on takeoff distance, and landing distance is affected by slope a bit less and wind a bit more. This would provide a good sense of how much a slope will affect the runway length you need. That penalty will certainly start to hurt as slope increases.

There is no firm guideline. It depends on wind conditions and other factors like the surrounding terrain.

I have landed at Jaffrey only uphill, which has a 0.9% grade and a bad surface, but people can and do land there downhill. It is very steep for an air strip. If the wind was strong enough I would have no problem landing downhill there, but with moderate winds I would always go uphill.

• OP wrote "Assume winds are not a factor."
– rbp
Dec 3, 2014 at 21:44
• Well, if there is no wind and no terrain you would normally land uphill on a graded runway if it has a listed gradient. Dec 3, 2014 at 22:14
• OP wanted to know how a grade figures into the aeronautical decision-making to land downhill or take off uphill, and if there's a rule-of-thumb. for example, runway 01 is 2500 feet long and downhill, and you're approaching from the south. Would you make a straight in, or circle at .5%? 1%? 5%?
– rbp
Dec 4, 2014 at 14:14