Learn what PULL UP and GLIDESLOPE aircraft warnings indicate, how their urgency differs, and the correct pilot or simulator response.
In real-world aviation, “PULL UP” is an urgent GPWS or TAWS command indicating an immediate terrain or obstacle threat and requiring the aircraft’s published escape manoeuvre. “GLIDESLOPE” is a caution that the aircraft has descended significantly below the ILS glidepath; correct safely or go around if the approach is unstable.
How are PULL UP and GLIDESLOPE warnings different?
PULL UP demands immediate terrain avoidance, while GLIDESLOPE warns that the aircraft is below its intended vertical approach path.
| Callout | What it means | Priority | Normal response |
|---|---|---|---|
| PULL UP | The aircraft is closing with terrain or an obstacle at an unsafe rate. | Immediate command warning | Execute the aircraft’s published terrain-escape manoeuvre. |
| GLIDESLOPE | The aircraft is excessively below the selected ILS glideslope. | Corrective alert that may become more insistent | Correct smoothly if the approach remains stable; otherwise go around. |
What exactly triggers a PULL UP warning?
PULL UP sounds when the ground-proximity system calculates that normal flight could result in contact with terrain or an obstacle. It is not simply a low-altitude announcement and should never be treated like the routine height callouts heard during landing.
Depending on the installed GPWS, enhanced GPWS or TAWS equipment, possible triggers include:
- Excessive descent rate for the aircraft’s height above the ground.
- Rapid terrain closure, even when the aircraft is not descending steeply.
- Predictive terrain or obstacle conflict derived from position and terrain-database information.
The exact escape procedure is aircraft-specific. It commonly involves maximum available thrust, the prescribed automation changes, minimal bank, an increase in pitch and retraction of speed brakes, while delaying flap or landing-gear changes until clear of terrain. Pilots must follow the aircraft flight manual and operator procedure rather than substitute a generic sequence.
What does GLIDESLOPE mean on an ILS approach?
The GLIDESLOPE aural alert normally means the aircraft is below the ILS glideslope by more than the warning system permits at that height. Traditional GPWS calls this Mode 5 protection.
It generally monitors deviation below the beam, not above it. On many installations the callout becomes louder or repeats more urgently as the deviation increases or the aircraft gets closer to the ground; the exact thresholds vary by system and aircraft.
The warning does not automatically mean that the glideslope transmitter or autopilot has failed. It reports excessive deviation from the signal being received. Our explanation of the difference between ILS vertical guidance and a localizer-only approach covers what remains available if the vertical component cannot be used.
Should the pilot correct the glideslope or go around?
A small, early deviation may be corrected smoothly, but a persistent or emphatic warning near the ground normally makes the approach unstable and calls for a go-around under operator criteria.
- Cross-check the guidance. Confirm the correct ILS, navigation source and approach indications, then compare the glideslope with altitude and distance checks.
- Correct without chasing the beam. If permitted by the stabilised-approach criteria, reduce the descent rate smoothly and regain the path without abrupt pitch or power changes.
- Go around when unstable. Discontinue the approach if the warning persists, the correction would be aggressive or any required approach gate is missed.
- Treat invalid guidance appropriately. If the glideslope fails or becomes unreliable, continue only when an authorised localizer-only procedure has been briefed and its separate minima can be met.
What if PULL UP and GLIDESLOPE sound together?
PULL UP takes priority over GLIDESLOPE because avoiding terrain is more urgent than recovering the ILS path. Execute the terrain-escape manoeuvre immediately; do not continue trying to recapture the glideslope or follow normal missed-approach altitude restrictions that compromise terrain clearance.
Can these warnings be false or misleading?
Both warnings can be false or operationally unnecessary, but crews initially treat them as genuine. A nuisance alert occurs when the equipment operates as designed during an unusual but understood flight path; a false alert can result from erroneous sensor, position, database or radio information.
PULL UP nuisance alerts may occur around steep terrain, unusual approved approaches or with faulty radio-altimeter or navigation data. GLIDESLOPE alerts can result from the wrong ILS being tuned, a localizer-only or back-course approach, receiver faults or disturbed ILS transmissions. Aircraft and vehicles near the antennas can affect the signal, which is why protecting the ILS critical area against guidance interference matters.
Some aircraft provide an approved glideslope-inhibit or cancellation function for approaches where that alert would be inappropriate. It is used according to procedure, not merely to silence a valid warning. At low altitude, the required safety response comes before fault diagnosis.
Why do these warnings sound in flight simulators?
In FSX, MSFS, X-Plane and Prepar3D, the same phrases may be generated by simplified gauge logic rather than a complete aircraft-standard GPWS or TAWS model. Troubleshoot them by examining what the simulated system believed at the moment of the alert.
- Check the flight path. Review radio altitude, vertical speed, terrain clearance and landing configuration. A scenery or terrain-elevation mismatch can produce a spurious PULL UP warning.
- Verify the ILS setup. Confirm the correct frequency, navigation source, inbound course and approach mode. Intercepting from above is a common reason the aeroplane fails to establish properly; our FSX glideslope-capture checklist covers the usual setup errors.
- Identify the source of the sound. A panel gauge, aircraft add-on or sound package may supply warnings independently of the simulator’s default avionics. The distinction between FSX GPWS warnings and ordinary landing-height callouts helps determine whether the alert represents actual terrain logic or a scripted sound.