Keep dropping below the ILS glideslope? Learn the causes, correct descent-rate and power errors, read the needle, and recover without chasing it.
You keep ending up below the ILS glideslope because your descent begins too early, your vertical speed is too high for groundspeed, or configuration and power changes let the aircraft sink. In real-world aviation and flight simulation, correct it by intercepting from below, stabilising early and making small trend corrections rather than chasing the needle.
Reading a below-glideslope indication
On a conventional raw ILS display, a glideslope pointer above centre means the beam is above the aircraft, so you are below the glideslope. A pointer below centre means you are above it. Do not confuse that pointer with a flight-director command bar, which tells you which way to pitch.
Being below the beam before capture is normal. Remain at the published intercept altitude while the glideslope pointer moves towards the centre; starting down before it arrives is one of the most common causes of remaining low. Our explanation of ILS beam geometry and interception from below covers why this technique prevents false or missed captures.
Why the aircraft drops below after capture
A low ILS path usually comes from an energy-management or guidance error rather than a fault in the glideslope itself.
| Cause | What happens | Correction |
|---|---|---|
| Descending before capture | The aircraft leaves the published intercept altitude while the beam is still above it. | Hold altitude until the pointer centres and the glideslope is captured. |
| Excessive vertical speed | A fixed descent rate is too steep for the aircraft's groundspeed. | Base the initial rate on groundspeed, then adjust using the pointer trend. |
| Late gear or flap extension | The sudden drag increase causes speed decay or a steeper descent. | Configure earlier and add the thrust needed to maintain target speed. |
| Chasing the pointer | Large pitch changes create repeated overshoots above and below the beam. | Use small corrections and wait to see whether pointer movement stops. |
| Wrong guidance mode or source | The autopilot continues in vertical-speed mode or follows another navigation source. | Check the ILS frequency, course, NAV source and captured mode annunciation. |
| Changing headwind | Groundspeed falls while the original descent rate remains unchanged, making the descent angle steeper. | Recalculate from groundspeed and reduce vertical speed as required. |
An incorrect pressure setting can place you at the wrong altitude before intercept and violate procedure constraints, but it does not directly change the radio glideslope indication after capture.
What descent rate keeps you on a 3-degree glideslope?
A three-degree glideslope requires approximately groundspeed x 5.2 in feet per minute. Multiplying groundspeed by five gives a quick cockpit estimate.
| Groundspeed | Approximate descent rate |
|---|---|
| 90 knots | 470 ft/min |
| 120 knots | 620 ft/min |
| 150 knots | 780 ft/min |
| 180 knots | 940 ft/min |
Use groundspeed, not indicated airspeed. Wind changes during the approach can alter the required rate, and some published glideslopes are not exactly three degrees, so the chart and glideslope pointer remain the final references.
Preventing a low ILS path
The most reliable prevention is to establish a stable aircraft before glideslope capture and avoid changing several variables at once.
- Verify the approach: confirm the runway, ILS frequency, inbound course, intercept altitude, minimum altitude and required navigation source.
- Stabilise speed and configuration: select the planned flap, gear and approach speed early enough that capture does not coincide with a major drag change.
- Intercept from below: establish on the localiser and hold the published altitude while the glideslope pointer descends towards centre.
- Confirm capture: check that the expected glideslope mode is captured, not merely armed. When hand-flying, begin the descent as the pointer centres.
- Set an initial descent rate: use groundspeed x 5.2, then trim and set enough power to hold approach speed.
- Watch the trend: if the pointer begins moving upwards, reduce the descent rate before the deviation becomes large.
For the wider procedure around these steps, see our complete ILS setup, intercept and landing sequence.
How should you recover when already below the glideslope?
Recover by making the descent shallower while maintaining approach speed; do not make a large pitch-up input simply to centre the pointer quickly.
- Confirm the indication: verify that the raw glideslope pointer is above centre and moving farther upwards.
- Reduce the sink rate: apply a small pitch correction and add power as needed to prevent airspeed loss.
- Stop the pointer movement: hold the corrected attitude until the pointer starts returning towards centre.
- Resume the normal descent: as it recentres, smoothly return towards the calculated descent rate rather than waiting for an overshoot.
A slight deviation normally needs only a shallower descent, not a climb. If recovering would require an aggressive manoeuvre, leave the aircraft unstable or take it below a published restriction, execute a missed approach instead.
Why does the autopilot still go below the glideslope?
A correctly coupled autopilot should track a valid glideslope, so a continuing low deviation usually means the mode never captured, the wrong source is selected, or the system has reached a control or trim limit.
- Mode: verify that glideslope capture is annunciated. Approach mode being armed is not the same as capture, and vertical-speed mode does not track the beam.
- Navigation source: confirm that the flight instruments and autopilot are using the tuned ILS rather than GPS or another receiver.
- Intercept geometry: establish on the localiser and approach the glideslope from below. Some systems will not capture reliably from above.
- Thrust: many autopilots control pitch but not power. The pilot must still prevent speed decay after flap or gear extension.
- Signal and aircraft state: check the correct runway ILS, identify the facility as required, and look for autopilot disconnects, excessive trim or control-axis interference.
FSX pilots with an armed APR mode that never changes to glideslope capture can work through our FSX-specific APR and glideslope capture checks. A large, persistent disagreement between the ILS and visual approach lights may also indicate the wrong facility or a simulator scenery and navigation-data mismatch; a small difference near the runway can result from antenna and eye-height geometry.
When should you abandon a low ILS approach?
Go around when the aircraft is no longer stabilised, the deviation is approaching full scale, airspeed or configuration is outside the applicable limits, or a safe correction cannot be completed before minimums.
Never descend below the decision altitude without the required visual references. Published procedures and operator stabilisation criteria take priority over trying to rescue an approach that has already become rushed or uncertain.