Originally Posted by
Double Back
In my B744 days I showed many a F/O, during X-wind landings, how the wind vector on the ND or PFD changed dramatically as soon as the PF decrabbed the beast, or when the A/P decrabbed it.
Yes, if you manouevre the aircraft from it's own stable, balanced state, the crosswind portion of the wind vector on the ND begins to become meaningless.
For example, if steadily tracking the localiser of an ILS towards landing, with a notable crosswind component, the wind vector will be shown accurately, as the aircraft will have drift angle into the crosswind, whilst remaining on the ILS centreline. However, should you then decide shortly before landing that you wish to conduct the landing using the wing-into-wind technique i.e. the upwind wing lowered with aileron to stop drift off centreline, then whilst the fore-and-aft axis of the aircraft is aligned with the runway using some opposite rudder, the nav computer cannot 'sense' the drift i.e. it cannot determine the crosswind component.
Consequently, in this now slightly cross-controlled situation, with the aircraft heading the same as runway alignment, maintaining the ILS centreline, and the nav computer not detecting any drift, the ND wind vector will
only display the applicable head or tailwind component, and display it as exactly that - a wind vector aligned with the aircraft heading, which itself is aligned with the runway!