Learn what an ILS hold line protects, how to recognise it, when to stop and how it differs from a runway holding position.
An ILS hold line is a marked holding position on a taxiway that keeps aircraft and vehicles outside an instrument landing system’s protected critical or sensitive area. When ATC instructs you to hold short of it, stop before the marking; crossing could distort the localiser or glide-slope signal used by landing aircraft.
In aviation and real-world flying, this is a signal-protection boundary, not a second runway edge. The protected area prevents nearby metal objects from reflecting or blocking the radio signals described in our explanation of how an ILS approach provides runway guidance.
How do you recognise an ILS hold line?
An ILS hold line is usually identified by a distinctive pavement marking, an adjacent mandatory sign and the airport chart. Its formal name may be ILS critical-area holding position marking or ILS sensitive-area holding position.
- Pavement marking: at many airports it resembles a yellow ladder, with two parallel solid lines joined by pairs of transverse bars across the taxiway.
- Sign: a red sign with white lettering may show ILS, CAT II, CAT III or a runway designation with category information.
- Chart: the airport diagram may label an ILS holding position, critical area or sensitive area boundary.
Markings and sign wording vary between countries. Use all three clues rather than assuming that every yellow ladder marking follows exactly the same local procedure.
Why must aircraft stay behind the ILS hold line?
The hold line prevents aircraft and vehicles from disturbing the radio guidance received by an aircraft on approach. The localiser antenna is normally beyond the far end of the runway, while the glide-slope antenna is positioned beside it; a large metal object in the wrong place can reflect their signals and produce erroneous cockpit indications or autopilot commands.
The critical area is the zone where an obstruction can cause unacceptable interference. A sensitive area is generally a larger protected zone used when tighter signal integrity is required. In everyday radio calls, “ILS critical area” is sometimes used for the protected area as a whole.
Protection becomes especially significant during low-visibility approaches and automatic landings. Our guide to ILS categories and their operating requirements explains why Category II and III procedures often require more restrictive holding positions.
When must a pilot stop at an ILS hold line?
Stop whenever ATC instructs you to hold short of the ILS critical or sensitive area, or when published local procedures require that holding position to be used.
- Identify the correct marking. An ILS hold line may be considerably farther from the runway than the normal runway holding position.
- Keep the whole aircraft clear. Stop with the nose, wings and tail on the holding side; merely keeping the nosewheel behind the paint is not enough.
- Wait for onward authorisation. Do not cross simply because the approaching aircraft has landed. Another protected approach may be following.
- Resolve any ambiguity. If the taxi clearance, sign and pavement marking appear to conflict, stop and ask ATC.
The marking remains painted throughout the year, but its operational protection may depend on visibility, the approach in use and local rules. At a non-towered aerodrome, follow the published airport procedure rather than inventing a visibility threshold yourself.
How is an ILS hold line different from a runway hold line?
An ILS hold line protects radio guidance, while a runway holding position protects the runway itself from an incursion.
| Feature | ILS holding position | Runway holding position |
|---|---|---|
| Purpose | Protects the localiser and glide-slope signals | Keeps aircraft and vehicles off an active runway |
| Common marking | Two solid yellow lines with ladder-like crossbars | Two solid and two dashed yellow lines |
| Typical location | May be well back from the runway | Near the runway entry or protected strip |
| Associated wording | ILS, critical area, sensitive area or CAT II/III | Runway designation |
At some airports one holding position serves both purposes. Never taxi to the more distant-looking line by guesswork; the chart, signs and ATC instruction determine which boundary applies.
Does an ILS hold line matter in a flight simulator?
Following an ILS hold line still matters for realistic simulator procedures, even when built-in ATC does not mention it. Many consumer simulators do not fully model signal disturbance from taxiing aircraft, and older or third-party scenery may contain missing or misplaced markings.
Use the charted position and signage when practising low-visibility operations. Our guide to finding ILS frequencies, courses and airport chart data covers the information needed to match an approach with its runway. If a simulator chart and rendered scenery disagree, treat that as a scenery or navigation-data mismatch; in real flying, the approved current chart and ATC instructions take precedence.