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When a plane comes into an airport to land, they will attempt to land on
the runway which is best aligned with the wind. This means that when landing,
pilots attempt to land "into the wind" as much as possible. This
gives the plane the greatest amount of airflow over the wings, and
therefore greater lift, without an increase in speed.
Before landing, pilots obtain weather
information, either from ATIS (automatic terminal information service),
ASOS (automatic surface observation service),
AWOS (automated weather observation system), HIWAS (hazardous inflight
weather advisory service), or from ATC.
The wind is reported as the magnetic direction
that the wind is blowing from, followed by the speed in knots (Nautical
miles per hour). There is other important information obtained as well, but
for this discussion, we will talk about the wind part only.
For example:
An ATIS broadcast for Hobby airport may sound
like this:
"Hobby airport information sierra,
two two five zero
Zulu weather, wind one five zero at eight, visibility one zero, sky
condition, few clouds at three thousand, temperature two eight, dew point
two six, altimeter two niner niner eight."
The reported wind is "one five zero at eight",
which means that the wind is coming out of the south, from a bearing of
150° degrees, at 8 knots. The preferred landing
runway should be oriented toward the south, as close to this bearing as
possible. If we look at the
diagram for Hobby airport, we see that there is one runway that is
predominately to the south, and that is runway 17/35. When landing
on this runway, with a wind from 150°, the pilot would have a slight
left headwind do deal with, but still aligned "into the wind", more than
any other runway, and this would be the best choice for landing in this
situation.
If runway 17/35 were not available (due to
closure or other traffic reasons), then the next best runway would be
one of the 12 runways (12R or 12L), giving the pilot a right headwind.
Some airports have different criteria for landing and departing traffic,
based on approach / departure requirements, ground handling, or other
issues. At KIAH airport, the 15/33 runways are almost always used
for takeoffs, and the 26's and 27 are almost always used for landing.
This works well due to the layout of the airport, since the terminal is
in the middle, they land and taxi right up to the terminal, and when
they depart, they taxi right out to 15L or 15R and depart without any
extended taxi. Even if the wind is somewhat out of the south, they will
usually continue to
operate this way. The reasoning is this:
The runway selection at a
large airport based on wind is predicated by the planes taking off,
not the planes that are landing. The
planes in the air are already airborne, and if a problem arises,
they can go around. However, a plane on the ground needs all
the help it can get (by being as much "into the wind" as possible)
to takeoff.
This usually works well at Bush
airport, the larger jets can handle a pretty strong crosswind and not
have too many problems landing on a runway that is not perfectly aligned
with the wind. Pilots flying into larger tower controlled airports
will follow the instructions of ATC as to which runway to land on.
However, if a pilot is flying into an uncontrolled field, both takeoff
and landing will be into the wind as much as possible.
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