Pilot/Controller Glossary 

9/5/24 

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. 
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 determined by joint processing of the 

time-difference-of-arrival (TDOA) measurements computed between a reference and the ground stations’ 

measured time-of-arrival. 

WILCO

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I have received your message, understand it, and will comply with it. 

WIND GRID DISPLAY

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 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. 
WIND SHEAR

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 A change in wind speed and/or wind direction in a short distance resulting in a tearing or 

shearing effect. It can exist in a horizontal or vertical direction and occasionally in both. 
WIND SHEAR ESCAPE

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 An unplanned abortive maneuver initiated by the pilot in command (PIC) as a result 

of onboard cockpit systems. Wind shear escapes are characterized by maximum thrust climbs in the low altitude 

terminal environment until wind shear conditions are no longer detected. 
WING TIP VORTICES

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(See VORTICES.) 

WORDS TWICE

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a. 

As a request: “Communication is difficult. Please say every phrase twice.” 

b. 

As information: “Since communications are difficult, every phrase in this message will be spoken twice.” 

WS

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(See SIGMET.) 
(See WEATHER ADVISORY.) 

WST

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(See CONVECTIVE SIGMET.) 
(See WEATHER ADVISORY.) 

PCG W

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