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.
What does your POH/AFM says?
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 ...
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.
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.