A320 cockpit approach - night conditions, terrain proximity

By Paul Toensing  |  Custom GPT Solutions  |  April 2026  |  ~8 min read

The Scenario

Night. Non-precision approach into a terrain-challenged airport. You have flown this arrival six times this month, and on four of those approaches the EGPWS fired a TERRAIN caution that turned out to be nothing. The high rate of descent required by the procedure consistently triggers the alert. You and the captain have developed a shared shorthand for it: a glance, a nod, continue.

Tonight you are configured - gear down, landing flaps, stable at 800 ft AAL. The EGPWS fires again. TERRAIN.

The glance. The nod.

This time, the terrain is real.

Two forces put you here, and understanding them is the difference between a recovery and an accident report.

Two Modes, Two Questions, One Aircraft

The EGPWS is not a single system asking a single question. It is a collection of modes, each asking a different question about your relationship with the ground. The two that matter most on approach are Mode 2 and Mode 4 - and they behave very differently depending on your configuration.

Mode 2: Am I Closing on Terrain Too Fast?

Mode 2 measures radio altitude and radio altitude rate of change - your closure rate with the ground. It has two sub-modes. Mode 2A is active during climb, cruise, and initial approach with gear up and flaps not in landing position. Mode 2B activates during approach and for 60 seconds after takeoff.

Here is where it gets interesting. With gear up, Mode 2 provides both a caution (TERRAIN, TERRAIN) and a warning (PULL UP). Two tiers of protection. But with gear down and landing flaps, Mode 2B reduces to caution only. The PULL UP warning disappears from Mode 2's repertoire entirely.

Read that again. In the configuration where you are lowest, slowest, and closest to terrain, Mode 2 deliberately limits itself to a caution. The warning-level protection is gone.

Mode 4: Am I Too Low for My Current Configuration?

Mode 4 measures terrain clearance against your configuration and speed. But here is the critical distinction the FCOM makes: Mode 4 is defined as "unsafe terrain clearance when not in landing configuration." Its sub-modes each protect against a specific configuration gap:

Mode 4A: gear up (aural: TOO LOW TERRAIN)
Mode 4B: gear down but flaps not in landing position (aural: TOO LOW GEAR or TOO LOW TERRAIN)
Mode 4C: takeoff phase (aural: TOO LOW FLAPS or TOO LOW TERRAIN)

Each sub-mode addresses a configuration gap. Once you are fully configured for landing - gear down, landing flaps - the gaps Mode 4 was designed to catch no longer exist. Mode 4's primary protections are not designed for your situation.

The Configuration Gap

Here is the trap the system creates:

A terrain threat with a stable closure rate can trigger Mode 4 without triggering Mode 2 - you are not closing fast, you are just too low. A high closure rate event can trigger Mode 2 without triggering Mode 4 - you are closing on terrain fast, but your configuration is appropriate for the altitude. The two modes are not redundant. They protect against different threats.

But the critical vulnerability emerges in landing configuration. Mode 2 has already reduced to caution-only. Mode 4's key protections are tied to being not configured for landing. So when you are fully configured, lowest, and slowest, both systems have reduced their sensitivity at the same time.

This is not a flaw. Airbus designed the system this way to reduce nuisance alerts in normal approach profiles where you are intentionally descending close to terrain. The problem is not the engineering. The problem is the pilot who does not know the engineering.

In landing configuration, the remaining terrain protection depends on Mode 1 (excessive descent rate), the predictive Terrain Clearance Floor (TCF) function - if the TERR pushbutton has not been pressed - and the crew's own situational awareness. The TCF is a separate predictive GPWS function (not a Mode 2 function) that warns of descent below a stored clearance floor regardless of aircraft configuration, with the aural TOO LOW TERRAIN. This distinction matters: pressing the TERR pushbutton removes TCF but does not touch Modes 1-5.

The Inhibition Architecture

TERR pushbutton OFF: Inhibits the Terrain Awareness Display (TAD) and Terrain Clearance Floor (TCF) functions. Does NOT inhibit basic GPWS Modes 1-5. Many pilots believe pressing TERR "turns off the GPWS warnings." It does not. Mode 2 and Mode 4 remain active. But TCF - which generates TOO LOW TERRAIN regardless of configuration - is gone. In landing configuration, TCF may have been your most configuration-independent terrain protection. And you just turned it off.

FLAP MODE pushbutton OFF: Inhibits Mode 4 flap-related protection (TOO LOW FLAPS) to avoid nuisance warnings when landing with a reduced flap setting.

LDG FLAP 3 pushbutton ON: Same inhibition specifically for CONF 3 landings.

SYS pushbutton OFF: Inhibits all basic GPWS modes 1-5. This is the nuclear option. It silences Mode 2, Mode 4, and everything else.

The Conditioned Response

The FCOM and FCTM do not use the term "conditioned distrust." But the operational manuals acknowledge that nuisance GPWS terrain warnings occur. Company arrival briefings for terrain-challenged airports explicitly warn crews that high rates of descent "might cause nuisance GPWS terrain warnings." The airline knows the warnings will fire. The crew knows the warnings will fire.

And after the fourth approach where the warning fires and nothing happens, something shifts in the crew's response. The urgency drains out of the alert. It becomes furniture. The startle response - the one that was designed to save your life - erodes precisely because the system worked correctly three times before. The fourth time, it is still working correctly. But the crew's response has changed.

The sim gives you crisp, unambiguous PULL UP scenarios where the correct response is obvious. Real operations give you repeated TERRAIN cautions on familiar approaches where the correct response is to continue - until the one time it is not, and by then the conditioned nod has already replaced the conditioned response.

The Professional Response: The Escape Maneuver

If a PULL UP warning fires, execute the PULL UP escape maneuver immediately:

Simultaneously: AP OFF, PITCH FULL BACKSTICK (and maintain), THRUST LEVERS TOGA, SPEED BRAKES CHECK RETRACTED, WINGS LEVEL.

Do not change configuration (gear/flaps) until clear of the obstacle. Respect stall warnings, not normal pitch attitudes - the maneuver demands approximately 20 degrees or more as required. Do not delay for analysis. There is no step in the procedure that says "check if this is a nuisance first."

The maneuver is engineered for maximum immediate climb performance. Maintaining current configuration is critical - retracting flaps or gear creates a transient sink rate that destroys vertical margin at the exact moment you need it most. Flight Directors and managed modes may not provide escape-optimized commands. Airbus philosophy requires raw pitch and thrust control, prioritizing obstacle clearance even if pitch attitudes exceed approach or go-around norms.

Important: after leaving PULL UP warning conditions but still in a Mode 2 triggered state, the aural changes to TERRAIN (repeated) while the PULL UP red lights remain on. Do not interpret the aural change as an "all clear." The lights are telling you the threat has not resolved.

Test Your Knowledge

If someone asked you right now which EGPWS modes lose protection in landing configuration, which alerts the TERR pushbutton actually inhibits, and what drives TOO LOW FLAPS versus TOO LOW TERRAIN - could you answer without reaching for the manual?

The difference between knowing the system and trusting the system is the difference between reacting to a warning and dismissing it. One of those decisions you can walk away from. The other you cannot.