In article ,
john89 wrote:

Hello everybody,

I got a question regarding the so-called "elevation", i.e. the highest
point of a runway. I have been told that the elevation is usually at
the threshold, right before the touchdown zone, in order to ensure an
easier take-off.
However, as airplanes land in the same direction as they take off,
isn't the descending RWY a problem for landing? My (admittedly
unprofessional) reasoning suggests that it would be better for aircraft
to land on RWYs increasing in altitude.
Am I completely off the track? Any experts out there, please help ;-)

Don't forget that most runways are also used in both directions
depending on wind, so that a sloping runway which is uphill for takeoff
in one direction becomes downhill for takeoff in the other.

Most runways are roughly level. If the money is available and the
terrain is amenable enough to be able to decide that one point on the
runway should be the highest point, then it should be enough to decide
that the runway should be level altogether and not have a single highest
point. This is usually considered the goal of making a runway.

Many runways are only roughly level, and contain small but noticeable
slopes. This is especially true at smaller airports. These slopes are
usually hard to discern from the ground (although I'm sure people will
chime in with counterexamples here) and don't affect aircraft
performance significantly.

There are a few airports whose runways are significantly sloped. You are
correct that aircraft are better off taking off downhill and landing
uphill. On runways like this, the aircraft will do exactly that, and
thus will take off and land in opposite directions. In a case like this,
using the slope appropriately is more important than operating into the
wind, so the typical performance reason for taking off and landing in
the same direction isn't there.

So in short, most runways are more or less level, and so takeoff/landing
direction isn't determined by slope. When the slope is significant, take
off downhill, land uphill.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon