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Pilot/Controller Glossary

WA

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(See AIRMET.)
(See WEATHER ADVISORY.)

WAAS

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(See WIDE-AREA AUGMENTATION SYSTEM.)

WAKE RE

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CATEGORIZATION (RECAT)

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 A set of optimized wake separation standards, featuring an

increased number of aircraft wake categories, in use at select
airports, which allows reduced wake intervals.

(See WAKE TURBULENCE.)

WAKE TURBULENCE

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 A phenomenon that occurs when an aircraft develops lift and forms a
pair of

counter

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rotating vortices.

(See AIRCRAFT CLASSES.)
(See VORTICES.)
(Refer to AIM.)

WARNING AREA

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(See SPECIAL USE AIRSPACE.)

WAYPOINT

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A predetermined geographical position used for route/instrument
approach definition, progress

reports, published VFR routes, visual reporting points or points for
transitioning and/or circumnavigating

controlled and/or special use airspace, that is defined relative to a V
ORTAC station or in terms of

latitude/longitude coordinates.
WEATHER ADVISORY

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 In aviation weather forecast practice, an expression of hazardous
weather conditions

not predicted in the Aviation Surface Forecast, Aviation Cloud
Forecast, or area forecast, as they affect the

operation of air traffic and as prepared by the NWS.

(See AIRMET.)
(See GRAPHICAL AIRMEN'S METEOROLOGICAL INFORMATION.)
(See SIGMET.)

WEATHER RECONNAISSANCE AREA (WRA)

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 A WRA is airspace with defined dimensions and published

by Notice to Air Missions, which is established to support weather
reconnaissance/research flights. Air traffic

control services are not provided within
WRAs. Only participating weather reconnaissance/research aircraft

from the 53

rd

 Weather Reconnaissance Squadron and National Oceanic and Atmospheric
Administration

Aircraft Operations Center are permitted to operate within a WRA. A WRA
may only be established in airspace

within U.S. Flight Information Regions outside of U.S. territorial
airspace.

WHEN ABLE

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a.

In conjunction with ATC instructions, gives the pilot the latitude to
delay compliance until a condition or

event has been reconciled. Unlike "pilot discretion," when instructions
are prefaced "when able," the pilot is

expected to seek the first opportunity to comply.

b.

In conjunction with a weather deviation clearance, requires the pilot
to determine when he/she is clear of

weather, then execute ATC instructions.

c.

Once a maneuver has been initiated, the pilot is expected to continue
until the specifications of the

instructions have been met. "When able," should not be used when
expeditious compliance is required.
WIDE-AREA AUGMENTATION SYSTEM (WAAS)

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 The WAAS is a satellite navigation system consisting

of the equipment and software which augments the GPS Standard
Positioning Service (SPS). The WAAS

provides enhanced integrity, accuracy, availability, and continuity
over and above GPS SPS. The differential

correction function provides improved accuracy required for precision
approach.

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