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Pilot/Controller Glossary

3/29/18

PCG W−1

W

WA−

(See AIRMET.)
(See WEATHER ADVISORY.)

WAAS−

(See WIDE-AREA AUGMENTATION SYSTEM.)

WAKE TURBULENCE− Phenomena resulting from

the passage of an aircraft through the atmosphere.

The term includes vortices, thrust stream turbulence,

jet blast, jet wash, propeller wash, and rotor wash

both on the ground and in the air.

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

WARNING AREA−

(See SPECIAL USE AIRSPACE.)

WAYPOINT− A predetermined geographical posi-

tion 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 VORTAC station

or in terms of latitude/longitude coordinates.
WEATHER ADVISORY− 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 SIGMET.)

WEATHER RECONNAISSANCE AREA (WRA)−

A WRA is airspace with defined dimensions and

published by Notice to Airmen, 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−

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)− 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.

WIDE AREA MULTILATERATION (WAM)– A

distributed surveillance technology which may

utilize any combination of signals from Air Traffic

Control Radar Beacon System (ATCRBS) (Modes A

and C) and Mode S transponders, and ADS-B

transmissions.  Multiple geographically dispersed

ground sensors measure the time-of-arrival of the

transponder messages. Aircraft position is deter-

mined by joint processing of the

time-difference-of-arrival (TDOA) measurements

computed between a reference and the ground

stations’ measured time-of-arrival.

WILCO− I have received your message, understand

it, and will comply with it.

WIND GRID DISPLAY− A display that presents the

latest forecasted wind data overlaid on a map of the

ARTCC area. Wind data is automatically entered and

updated periodically by transmissions from the

National Weather Service. Winds at specific

altitudes, along with temperatures and air pressure

can be viewed.