Back Course (BC) is defined as which of the following?

• A. The reciprocal of the localizer course for an ILS.
• B. The front course of an ILS.
• C. A heading alignment for a TACAN approach.
• D. The reciprocal of the localizer course for an ILS; used when approaching from the end where the localizer antennas are installed.

Answer: (D)

Back Course means using the localizer in reverse: it is the reciprocal of the ILS localizer course, and it’s used when you’re approaching the runway from the opposite end—specifically from the direction where the localizer antennas are located. Because you’re coming from the far end, you set or interpret the localizer signals in a way that aligns with flying toward the runway centerline from that direction. The localizer still gives lateral guidance, but the sense of the needle is reversed unless you’re using the reciprocal course, so you fly the approach by tracking that reciprocal course to stay on the centerline.