4/20/23 

Pilot/Controller Glossary 

W 

WA

−

 

(See AIRMET.) 
(See WEATHER ADVISORY.) 

WAAS

−

 

(See WIDE-AREA AUGMENTATION SYSTEM.) 

WAKE RE

−

CATEGORIZATION (RECAT)

−

 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

−

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

counter

−

rotating vortices. 

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

WARNING AREA

−

 

(See SPECIAL USE AIRSPACE.) 

WAYPOINT

−

 

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 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 GRAPHICAL AIRMEN’S METEOROLOGICAL INFORMATION.) 
(See SIGMET.) 

WEATHER RECONNAISSANCE AREA (WRA)

−

 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

−

 

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. 

PCG W

−

1