Landing With Wind Gradient Or Wind Shear

T-39 FLIGHT PREPARATION

STUDENT GUIDE

surface conditions. Some airfields report runway braking characteristics in accordance with

ICAO documents, that is "good", "medium", and "poor". In order to relate these ICAO

categories to an RCR or when RCR values are not available, the following relationship will

be used.

RUNWAY

ICAO REPORT

RCR

CONDITION

Dry

Good

Wet

Medium

Icy

Poor

b. Landing With Wind Gradient Or Wind Shear.

Wind velocity is generally higher a short distance above the runway than it is on the

runway itself. Entering this wind gradient during the landing approach could result in a

change in airspeed which requires correction.

When landing with a headwind, more thrust is required to maintain a desired glide path

than is necessary with no wind. Also, the decreasing magnitude of the headwind in the

gradient can cause a decrease in airspeed which has to be counteracted with the use of

additional thrust to prevent a possible short landing. With a tailwind during the landing

approach, the proper glide slope is maintained with a lower thrust setting, and since the

magnitude of the tailwind is decreasing during penetration of the wind gradient, airspeed may

have a tendency to increase, requiring a reduction in thrust. If these corrective measures are

not taken, there is a possibility of over-shooting the runway, necessitating a go-around.

The effect of crosswind will also be considered during the landing approach. As the

aircraft approaches the runway, less correction for crosswind may be required to maintain the

proper flight path.

The degree of corrective action necessary during an approach is dependent upon the

severity of the wind gradient. With a sharp gradient, the change in airspeed could be very

rapid, requiring an immediate correction. The combination of wind gradient, plus wind that

is intermittent or variable in direction and/or speed, requires caution always be exercised

during the landing approach. The corrections below summarize landing data corrections

required due to wind effects.

c. Wind Corrections

Accounting for wind in planning the landing requires the wind direction and speed be

known. The headwind (or tailwind) and crosswind components can then be determined using

the TAKE-OFF AND LANDING CROSSWIND chart in the PCL.

G-8