Definition
An instrument approach that uses the back-course signal of an Instrument Landing System (ILS) localizer for lateral guidance to a runway. The localizer transmits a directional signal aligned with one runway, but a usable signal also extends in the opposite direction behind the antenna. A back-course approach uses that opposite-direction signal to line up with the reciprocal runway. It provides lateral (left-right) guidance only, with no glideslope, so descent is flown using published step-down altitudes.
Plain English
An approach that uses the signal coming out the back side of the ILS antenna to line you up with the runway at the opposite end. You get steering left and right, but no automatic up-and-down guidance, so you step down to your minimums using published altitudes.
Context Anchor
Seen on instrument approach charts, often labeled “LOC BC,” meaning localizer back course, and in instrument training discussions about localizer indications.
Derivation
The localizer antenna sits at the far end of a runway and transmits a directional beam down the runway centerline (the front course). The same signal radiates out the back of the antenna, called the back course. An approach flown using that rear lobe is therefore a back-course approach.
Why Pilots Care
The procedure expands usable approach options but produces reverse CDI sensing, requiring pilots to fly away from the needle rather than toward it to stay on course.
Grounding Statement
Picture approaching a runway by following the opposite side of the same radio alignment path normally used from the other direction.
Intuition Check
Back-course does not mean the airplane is flying backward or that the pilot should ignore normal approach procedures. It means the approach uses the opposite side of the localizer signal, and the left-right indication may need special attention.
Example Sentence 1
Because the front course was out of service, the controller cleared us for the back-course approach to the opposite runway.
Example Sentence 2
On the back-course approach the CDI showed reverse sensing, so the pilot turned away from the needle to recenter the course.