Do you need an ADF for an ILS approach? Learn why the answer is usually no, when an NDB changes it, and what to check on the chart.
No. An ADF is not part of the basic ILS: the aircraft uses a VHF NAV receiver to receive localiser and glideslope guidance. You need an ADF only when the published procedure uses an NDB for a required fix, transition or missed approach and no approved substitute is available.
In aviation and real-world flying, an ADF and an ILS are separate radio-navigation systems. The ADF points towards an NDB; it does not receive either component of an ILS.
What equipment actually receives an ILS?
An ILS-capable NAV receiver receives the approach guidance. Selecting the published localiser frequency also pairs the associated UHF glideslope channel automatically, including on integrated flight decks where the radio may be tuned through a management system.
| Signal or aid | Purpose | Receiver | Required for a basic ILS? |
|---|---|---|---|
| Localiser | Lateral guidance | VHF NAV/ILS receiver | Yes |
| Glideslope | Vertical guidance | Paired glideslope receiver | Yes, for full ILS minima |
| NDB | Bearing or fix identification | ADF | Only when the procedure requires it |
| DME | Distance and fix identification | DME equipment or an authorised substitute | Only when specified |
The autopilot is optional; the indications can be hand-flown. If the glideslope is unavailable, the procedure may be flown only as a localiser approach when the chart provides localiser-only minima. Our explanation of how the glideslope and localiser work together covers the signal behaviour in more detail.
When does an ILS approach require an ADF?
An ILS can require an ADF when an NDB supports another part of the published procedure rather than the final ILS guidance itself. Common examples include:
- An NDB used as an initial approach fix or holding fix.
- A locator outer marker or other NDB used to identify a procedure point.
- An NDB transition feeding the localiser.
- A missed-approach instruction requiring tracking to or from an NDB.
- A chart note explicitly stating that ADF is required.
An NDB symbol appearing on the chart does not automatically make the ADF mandatory. It must be required for the route or fix being flown, and there must be no permitted alternative way to identify that point. Radar vectors or an RNAV transition may avoid an NDB segment, but only when the clearance and procedure allow it.
How can you tell whether the approach needs an ADF?
The approach chart determines the equipment requirement, not the fact that the procedure is labelled ILS.
- Read the equipment notes. Look for wording such as
ADF required, particularly where an NDB supports the missed approach. - Trace the route you will fly. Check the transition, holding pattern, plan view, profile and missed-approach path for an NDB fix.
- Check how each fix is identified. DME, marker beacons, crossing radials or approved GNSS may provide an alternative, depending on the chart and operating rules.
- Verify aircraft capability. In real operations, the substitution must be permitted by the installed equipment, applicable authority and operator procedures.
- Check chart and navigation-data agreement. In a simulator, mismatched scenery, chart and navigation-data cycles can leave an NDB or waypoint missing.
Can GPS replace the ADF on an ILS approach?
Approved GNSS equipment can sometimes substitute for an NDB used to identify a fix, but that permission is procedure- and jurisdiction-dependent. The fix must be present in the navigation database, and the aircraft installation and operating rules must allow the substitution.
GPS does not replace the ILS localiser or glideslope. If flying to ILS minima, final guidance still comes from the ILS receiver; GPS may supply the route to the approach or help identify supporting fixes.
What should you set in a flight simulator?
For a normal simulated ILS, tune or confirm the published ILS frequency, set the inbound course where the aircraft requires it, verify the identifier and select the NAV or VLOC source rather than GPS before capture. A mistake we see constantly is a correctly tuned frequency with the display still sourcing its deviation needle from GPS.
Intercept the localiser on a sensible angle and join the glideslope from below at the charted altitude. Use the ADF only if the selected transition, fix or missed approach needs an NDB. For the complete sequence, follow our practical ILS tuning and capture procedure.