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 MIL-HDBK-1021/1
d) Wind Distribution. Determine wind distribution to accompany
instrument flight rule (IFR) conditions when considering orientation of an
instrument runway.
3.1.3
Use of Wind Rose Diagrams. For a typical wind rose diagram (relative
frequency and average strength of winds from different directions), components,
and supporting data, see Figure 1. Prepare a wind rose diagram for each new
runway in the planning stage.
a) Special Conditions. Wind rose diagrams for special meteorological
conditions, such as wind velocities and directions during IFR conditions, should
be prepared when necessary for local airfield needs.
(1) Wind Direction. Use radial lines to represent compass
directions based on true north, and concentric circles, drawn to scale, to
represent wind velocities measured from the center of the circle.
(2) Calm Wind. Use the innermost circle to encompass calm periods
and wind velocities up to the allowable crosswind component for the airfield
under consideration (15 knots or 17.3 miles per hour on Figure 1).
(3) Computations. Compute percentages of time that winds of
indicated velocities and directions occur, and insert them in the segments
bounded by the appropriate radial direction lines and concentric wind velocity
circles. Express percentages to the nearest tenth, which is adequate and
consistent with wind data accuracy.
b) Desired Runway Orientation. For the use of wind rose diagrams in
determining desirable runway orientations with respect to wind coverage, see
Figure 2.
3.2
Wind Coverage Requirements for Runways.
Place runways to obtain at
least 95 percent wind coverage.
3.2.1
Primary Runways. Orient a primary runway for the maximum possible wind
coverage. See Figure 2 for the method of determining wind coverage.
3.2.2
Secondary Runways. Where wind coverage of the primary runway is less
than 95 percent or in the case in some localities where during periods of
restricted visibility the wind is from a direction other than the direction of
the primary runway, a secondary (crosswind) runway is required. Normally
secondary runways will not be planned without prior authorization from Naval Air
Systems Command. The secondary runway will be oriented so that the angle
between the primary and secondary runway longitudinal centerline is as near 90
degrees as is feasible considering local site conditions and the need to provide
maximum crosswind coverage.
3.2.3
Maximum Allowable Crosswind Components. Select these components
according to type of aircraft, as follows: (1) tricycle gear aircraft, 15.0
knots, and (2) conventional gear aircraft, 10.4 knots.
3.2.4
Allowable Variations of Wind Direction.
See Figure 3 for allowable
wind directions.
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