Pilot/Controller Glossary

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 53rd 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.