Learn what a back-course ILS approach is, how reverse sensing works, which mode to use, and how to fly the step-downs, MDA and missed approach.
A back-course ILS approach uses the localizer signal on the opposite side of its antenna from the normal front-course approach, providing lateral guidance towards the reciprocal runway. Fly only a published LOC BC procedure, configure the receiver or back-course mode correctly, ignore glideslope indications, follow charted step-down altitudes, and observe the MDA and missed-approach point.
In Aviation & Real-World Flying, the formal chart title is usually LOC BC, meaning localizer back course. Calling it an ILS is convenient shorthand, but it normally supplies lateral guidance only and is therefore a non-precision, or 2D, approach. Our explanation of how full ILS and localizer-only guidance differ covers that distinction in more detail.
How the back-course localizer works
An ILS localizer aerial normally radiates a front-course signal along the runway centreline and a signal behind the aerial in the reciprocal direction. A published back-course procedure uses that rear signal for an approach to the opposite runway end.
A receivable back-course signal does not by itself create an approach. The procedure must be published, available and suitable for the aircraft; in real-world flying, any applicable outage or restriction must also be checked. Do not improvise one by tuning the reciprocal runway's ILS.
The charted back-course final approach course is roughly reciprocal to the front course, but use the published figures rather than calculating them from the runway number. For an ordinary approach from the front side, follow the standard front-course ILS technique instead.
How to fly a back-course ILS approach
The safe sequence is to brief the complete LOC BC procedure, establish the correct lateral sensing before descent, then fly the charted fixes and altitudes to the published minimum.
- Confirm that LOC BC is published. Check the chart or simulator procedure list for the correct runway and localizer. A runway with an ILS in the opposite direction does not automatically have an authorised back-course approach.
- Brief the whole procedure. Note the localizer frequency and identifier, final approach course, required course-selector setting, intercept altitude, fixes, step-down restrictions, category-specific minimum, missed-approach point and missed procedure.
- Tune and identify the localizer. Select the correct NAV receiver or allow the approved avionics to tune it, then confirm the identifier where the simulation models it. Make sure the flight display is using NAV, LOC or VLOC rather than GPS/FMS guidance alone.
- Configure the course and sensing. Follow the aircraft or avionics manual. A traditional HSI commonly requires the front-course heading—the reciprocal of the LOC BC inbound course—to be selected. A basic CDI may retain reverse sensing regardless of its OBS setting, while an EFIS or dedicated BC mode may correct the indication automatically.
- Intercept at the charted altitude. Use the published procedure or ATC vector, normally with a modest intercept angle. Do not descend merely because the needle has become active.
- Verify the capture direction. Before relying on the indication or autopilot, confirm that the commanded correction leads towards the published centreline. If the aircraft turns away or the deviation grows, the source, selected course or back-course mode is wrong.
- Follow every altitude restriction. Cross each fix at or above its charted altitude and descend only when the procedure permits. There is no valid ILS glideslope to follow.
- Observe the minimum and MAP. Level at the published minimum—normally an MDA—unless the required visual references permit continued descent. If those references are absent at the missed-approach point, execute the published missed approach immediately.
Why does a back-course ILS show reverse sensing?
Reverse sensing occurs because a conventional localizer indicator is designed around the front course, so its needle may point towards the side from which a back-course pilot must turn away.
| Equipment configuration | Expected indication | Pilot action |
|---|---|---|
| Basic CDI without BC correction | Usually reverse sensing inbound | After confirming the installation's behaviour, correct away from the needle. The OBS knob often does not change localizer sensing. |
| Traditional HSI | Normally correct when configured as specified | Many installations require the front-course heading to be selected. Check the aircraft documentation rather than assuming. |
| EFIS or FMS with a coded LOC BC procedure | May provide normal left-right commands automatically | Verify the loaded procedure, active NAV source, selected course and BC or LOC mode annunciation. |
The mistake we see most often is memorising “fly away from the needle” and applying it to every cockpit. That rule is valid only when the instrument is actually displaying uncorrected reverse sensing. Dedicated back-course logic turns it into a normal command display, where the pilot follows the needle or flight director.
Does a back-course ILS have a glideslope?
A normal LOC BC approach has no authorised glideslope, even if the cockpit's glideslope pointer moves. Rear lobes, false signals or simulator modelling can produce a plausible-looking indication that must not be used for descent.
Use the barometric altimeter, charted distances or fixes, step-down altitudes, MDA and MAP. A charted descent angle, advisory VNAV path or calculated continuous descent may help with vertical planning where permitted, but it remains advisory and does not turn LOC BC into a precision ILS.
Can the autopilot fly a back-course approach?
An autopilot can fly the lateral portion only when its approved modes support back-course sensing or the loaded procedure supplies the correct guidance. A dedicated mode may be labelled BC or BCRS; other systems handle LOC BC through their approach database and flight-guidance logic.
Do not assume that pressing APP is correct. On some avionics, APP is part of the documented method for arming a coded back-course approach; on others it commands front-course localizer and glideslope capture and can produce the wrong turn. Verify the flight-mode annunciation, watch the first capture command and manage altitude or vertical speed separately.
If the aircraft has no supported BC mode and its LOC indication is reversed, hand-fly the lateral guidance. Disconnect immediately if an autopilot turns away from the centreline or commands an unexpected descent.
Common simulator failure modes
- The CDI moves the wrong way: the display is showing raw reverse sensing, the wrong course is selected, or the expected BC logic is not active. Confirm the specific aircraft's procedure before continuing.
- The localizer never captures: check the frequency, identifier, receiver, active NAV source and interception geometry. In MSFS 2024, the same source-selection checks used for NAV/VLOC and approach-mode setup apply here.
- The moving-map line and raw needle disagree: the aircraft's navigation database and the simulator's radio-navigation or scenery data may not match. Do not chase two conflicting guidance sources.
- APP captures an unexpected glideslope: disengage the mode and return to the documented LOC BC configuration. Any glideslope indication on a standard back-course approach is unusable.
- The procedure is missing: the simulator's navigation data may not contain it, or the real procedure may no longer exist. Do not substitute an improvised reciprocal ILS; choose another published approach.