.
Does not necessarily reflect the aircraft maximum crosswind capability; and,
.
Generally applies to a steady wind.
Nevertheless, a survey conducted by Airbus Industrie indicates that 75% of operators consider the maximum demonstrated crosswind as a limitation.
When no demonstrated gust value is available:
.
50% of operators consider that only the ATIS and tower average-wind must be lower than the maximum demonstrated crosswind; and,
.
50% of operators consider that the ATIS and tower gust must be lower than the maximum demonstrated crosswind.
The majority of operators have published and implemented reduced crosswind limits for operation on contaminated runway.
The crosswind limits published by operators for dry or wet runway and for runway contaminated with standing water, slush, snow or ice often are lower ( by typically 5 kt ) than the demonstrated values or recommended values published by Airbus Industrie.
Maximum Computed Crosswind
The maximum computed crosswind reflects the computed design capability of the aircraft in terms of:
.
Rudder authority;
.
Roll control authority; and,
.
Wheel-cornering capability.
Factors Affecting Crosswind Capability
The following factors, runway conditions or configurations affect the crosswind capability:
.
Runway condition (i.e., nature and depth of contaminant);
.
Systems malfunctions (e.g., rudder jam); or,
.
MEL conditions (e.g. nose wheel steering inoperative).
Wind Information on Navigation Display
Wind information on the navigation display (ND) consists of two elements, as shown on Figure 4:
. A wind arrow:
. The direction of the wind arrow is referenced to the magnetic north ( because the magnetic north is the reference for the ND map ) and reflects the wind direction;
. The length of the wind arrow is fixed (i.e., the length does not vary with varying wind velocity).
The wind arrow is the primary wind visual-cue during the final approach ( together with the ground speed [GS] display ).
. A digital wind information that provide the wind direction (referenced to the true north) and wind velocity.
The digital wind information is primarily used to compare the current wind to the predicted wind provided on the computerized flight plan.
Depending on aircraft models and standards, the wind information may be computed either by the inertial reference system (IRS) or by the flight management system (FMS).
Depending on the wind source, different time delays are applied for smoothing (i.e., averaging) the wind value.
What’s Your Current Wind ?
Page 3
The wind information on the ND is refreshed typically 10 times per second.
Figure 4
(Typical display)
IRS Wind
The IRS wind is assessed geometrically using the triangle consisting of the true air speed (TAS) vector, ground speed (GS) vector and wind vector.
The TAS vector and GS vector are defined by their velocity and direction, as follows:
.
TAS vector: . velocity: TAS from the air data computer
(ADC);
. direction: magnetic heading from IRS.
.
GS vector: . velocity: GS from IRS; . direction: magnetic track from IRS.
The IRS wind is computed and transmitted to the aircraft electronic flight instrument system (EFIS) for display on the navigation display (ND) typically 10 times per second.
The IRS wind display is therefore a near-real-time wind information.
FMS Wind
The FMS wind is computed similarly to the IRS wind but with the following differences:
.
The accuracy of the ground speed received from the IRS is increased by including a correction based on the DME-DME position or GPS position, when available; and,
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