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Aeronautical Information Manual (AIM), page 625

5/26/16
12/10/15

B
BACK-TAXI- A term used by air traffic controllers
to taxi an aircraft on the runway opposite to the traffic
flow. The aircraft may be instructed to back-taxi to
the beginning of the runway or at some point before
reaching the runway end for the purpose of departure

or to exit the runway.

BASE LEG-
(See TRAFFIC PATTERN.)
BEACON-
(See AERONAUTICAL BEACON.)
(See AIRPORT ROTATING BEACON.)
(See AIRWAY BEACON.)
(See MARKER BEACON.)
(See NONDIRECTIONAL BEACON.)
(See RADAR.)

BEARING- The horizontal direction to or from any
point, usually measured clockwise from true north,
magnetic north, or some other reference point
through 360 degrees.
(See NONDIRECTIONAL BEACON.)

BELOW MINIMUMS- Weather conditions below
the minimums prescribed by regulation for the
particular action involved; e.g., landing minimums,
takeoff minimums.

BLAST FENCE- A barrier that is used to divert or
dissipate jet or propeller blast.

BLAST PAD- A surface adjacent to the ends of a

runway provided to reduce the erosive effect of jet

blast and propeller wash.

BLIND SPEED- The rate of departure or closing of
a target relative to the radar antenna at which
cancellation of the primary radar target by moving
target indicator (MTI) circuits in the radar equipment
causes a reduction or complete loss of signal.
(See ICAO term BLIND VELOCITY.)

BLIND SPOT- An area from which radio
transmissions and/or radar echoes cannot be
received. The term is also used to describe portions
of the airport not visible from the control tower.

BLIND TRANSMISSION-
(See TRANSMITTING IN THE BLIND.)
Pilot/Controller Glossary

BLIND VELOCITY [ICAO]- The radial velocity of
a moving target such that the target is not seen on
primary radars fitted with certain forms of fixed echo
suppression.

BLIND ZONE-

(See BLIND SPOT.)
BLOCKED- Phraseology used to indicate that a
radio transmission has been distorted or interrupted
due to multiple simultaneous radio transmissions.
BOTTOM ALTITUDE– In reference to published
altitude restrictions on a STAR or STAR runway
transition, the lowest altitude authorized.
BOUNDARY LIGHTS-
(See AIRPORT LIGHTING.)

BRAKING ACTION (GOOD, MEDIUM, POOR,
OR NIL)- A report of conditions on the airport
movement area providing a pilot with a degree/qual-
ity of braking that he/she might expect. Braking
action is reported in terms of good, fair, poor, or nil.
Effective October 1, 2016, Braking Action will be
categorized in the following terms: Good, Good to
Medium, Medium, Medium to Poor, Poor, and Nil.
(See RUNWAY CONDITION READING.)

BRAKING ACTION ADVISORIES- When tower
controllers have received runway braking action
reports which include the terms "fair," "poor," or
"nil," or whenever weather conditions are conducive
to deteriorating or rapidly changing runway braking

conditions, the tower will include on the ATIS

broadcast the statement, "Braking action advisories

are in effect" on the ATIS broadcast. During the time
braking action advisories are in effect, ATC will issue
the latest braking action report for the runway in use
to each arriving and departing aircraft. Pilots should
be prepared for deteriorating braking conditions and
should request current runway condition information
if not volunteered by controllers. Pilots should also
be prepared to provide a descriptive runway
condition report to controllers after landing.
Effective October 1, 2016, the term "fair" will be
replaced with "medium".

BREAKOUT- A technique to direct aircraft out of
the approach stream. In the context of simultaneous
(independent) parallel operations, a breakout is used

PCG B-1

Page 625 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   624 -- Page 625 -- 626