Aviation Glossary - W

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w.e.f. - with effect from. Also w.i.e., with immediate effect.

WAAS - Wide Area Augmentation System (in USA)

wake turbulence - wingtip vortices generated behind a wing producing lift. Behind a large heavy aircraft they can be powerful enough to roll or even break up a smaller aircraft.

WAT - weight-and-temperature

wind shear - localised change in wind speed and/or direction over a short distance, resulting in a tearing or shearing effect, usually at low altitude, that can cause a sudden loss of airspeed with occasionally disastrous results if encountered when taking-off or landing.

WIP - work in progress.

WP - waypoint.

wt - weight

Wx - weather.

WX NIL - no significant weather, term used in Met reports.