WA U.S.: Abbreviation for: weather advisory
WAAS
U.S. and Canada: Abbreviation for: wide area augmentation system
Fr: WAAS
WAC Abbreviation for: world aeronautical chart Fr: WAC
wake turbulence
Turbulent air behind an aircraft caused by any of the following:
(a)
 wing-tip vortices;

(b)
 rotor-tip vortices;

(c)
jet-engine thrust stream or jet blast;

(d)
 rotor downwash;

(e)
 prop wash.

Fr: turbulence de sillage
warning area U.S.: A warning area is airspace of defined dimensions, extending from 3 NM outward from the coast of the United States, that contains activity that may be hazardous to nonparticipating aircraft. The purpose of such warning areas is to warn nonparticipating pilots of the potential danger. A warning area may be located over domestic or international waters or both.
WAS
Abbreviation for: Water Aerodrome Supplement
Fr: WAS
Water Aerodrome Supplement A joint civil/military publication concerning water aerodromes that is intended to be used to supplement en route charts and the Canada Air Pilot (CAP). This document is issued once a year.
.
abbreviation: WAS

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see also: Airport/Facility Directory (A/FD)

Fr: Supplément hydroaérodromes
way-point ICAO: Expression for: waypoint (WP)
waypoint A specified geographical location, defined by longitude and latitude, that is used in the definition of routes and terminal segments and for progress-reporting purposes.
. abbreviation: WP
Fr: point de cheminement
weather advisory U.S.: In aviation weather forecast practice, an expression of hazardous weather conditions not predicted in the area forecast, as they affect the operation of air traffic and as prepared by the National Weather Service (NWS).
. abbreviation: WA
weather information Other expression for: meteorological information
WGS-84 Abbreviation for: World Geodetic System 1984 Fr: WGS-84 
“When able…” U.S.: When used in conjunction with ATC instructions, gives the pilot the latitude to delay compliance until a condition or event has been reconciled. Unlike “at pilot’s discretion”, when instructions are prefaced “when able”, the pilot is expected to seek the first opportunity to comply. Once a maneuver has been initiated, the pilot is expected to continue until the specifications of the instructions have been met. Note: “When able” should not be used when expeditious compliance is required.
. see also: “When ready…”
“When ready…” Canada: When used in conjunction with an altitude clearance, means that ATC has offered the pilot the option of commencing the altitude change whenever the pilot wishes. When the change is initiated, the pilot should advise ATC. Pilots may temporarily level off at any intermediate altitude; however, once an altitude has been vacated, the pilot may not return to that altitude because ATC may have reassigned it to another aircraft. Pilots are expected to advise ATC of any temporary level-off at any intermediate altitude. Compliance with any assigned or published altitude crossing restriction is mandatory unless specifically cancelled by ATC. Fr: . Lorsque prêt… .