back course sector
The course sector that is situated on the opposite side of the localizer (LOC) antenna from the runway.
. see also: front course sector
Fr: secteur d’alignement de piste arrière
backtrack
The taxiing of an aircraft on a runway in use in a direction opposite to the landing or take-off direction.
Fr: circulation à contresens
balloon
A non-power-driven lighter-than-air aircraft. 
Fr: ballon
base Other expression for: base leg
base leg A flight path extending from the end of the downwind leg to the extended centreline of the approach end of the landing runway (or landing path).
. also called: base
Fr: étape de base
BCST Abbreviation for: broadcast Fr: BCST
beacon An aeronautical light arranged, either through optical design or mechanical motion, to be visible to all azimuths, either continuously or consecutively, to designate a particular point on the surface of the earth.
. also called: aeronautical beacon
Fr: phare
bearing The horizontal direction to or from any point, usually measured clockwise from true north, magnetic north or some other reference point, through 360°.
. abbreviation: BRG
Fr: relèvement
bedpost Other expression for: terminal area entry fix
below minimums
An expression indicating that the weather conditions are below the minimums prescribed by regulation.
Fr: en dessous des minimums
bird hazard A hazard relating to the conduct of flight operations that results from the presence of birds, primarily in the vicinity of an aerodrome. Fr: péril aviaire
bird strike
An incident deemed to have occurred whenever 
(a)
a pilot reports a bird strike;

(b)
aircraft maintenance personnel identify damage to an aircraft as having been caused by a bird strike; 

(c)
personnel on the ground report seeing an aircraft strike one or more birds; or

(d)
bird remains, whether in whole or in part, are found on an airside pavement area or within 200 ft of a runway, unless another reason for the bird’s death is identified.