Definition
A non-precision instrument approach that uses the back (reverse) signal of an ILS localizer antenna to provide lateral guidance to a runway opposite the one the localizer normally serves. It provides course guidance only — there is no glideslope — so the pilot descends using published step-down altitudes to a minimum descent altitude (MDA).
Plain English
An instrument approach that lines you up with the runway by using the signal coming out of the back side of an ILS antenna installed at the other end of the airport. It only gives you left-right guidance, not up-down, so you step down to published altitudes until you can see the runway.
Context Anchor
Seen in instrument approach procedures where a runway uses the reverse side of a localizer signal rather than the normal front-course localizer approach.
Derivation
Localizer' comes from 'localize' — to pinpoint a position — because the antenna pinpoints the runway centerline. 'Back course' simply means the signal radiating out the back of that antenna, opposite to its normal (front course) direction.
Why Pilots Care
Expands the number of runways that can be used for instrument approaches at airports equipped with only one localizer array, increasing access in low-visibility conditions.
Intuition Check
Back course does not mean flying backward, and approach does not mean any general arrival toward an airport. Here, it means a specific published instrument procedure using the opposite side of a localizer radio signal.
Example Sentence 1
With the ILS to Runway 27 out of service, the crew briefed and flew the localizer back course approach to Runway 9.
Example Sentence 2
During the localizer back course approach the crew flew headings opposite the published front-course inbound heading to stay on the localizer centerline.