Controls and Indications

The landing gear's cockpit interface is minimal: one two-position lever and three places to look. But knowing what to look at and what to trust matters — especially when a light does not agree with the others, and you need to know which indication is the most credible. This article covers the hand (the lever and its interlock) and the eye (the indication panel, the WHEEL SD page, and the red arrow). The information architecture behind the lights is in LGCIU and Position Warning.

1. The indication panel — three states, and "one green is enough"

The indication panel is fed by LGCIU 1, with one light per gear. Per FCOM DSC-32-10-30:

No light: Indicate landing gear is retracted and locked up... ▿ light: Illuminate green if the landing gear is locked down. UNLK light: Illuminate red if the landing gear is not locked in selected position.

Three states: no light = stowed and locked up; green ▿ = down and locked; red UNLK = not in the selected position (in transit or jammed).

A highly practical reading rule for when a UNLK will not extinguish on extension. Per FCOM DSC-32-10-30:

...only one green triangle on each landing gear is sufficient to confirm that the landing gear is downlocked.

Why: each leg has two independent channels (LGCIU 1 / LGCIU 2), and the WHEEL page shows two triangles per gear. If either channel reports "downlocked" (one green triangle), the leg is locked — because downlock is a physical fact, and one sensor confirming it is credible. So if a panel UNLK red light persists, look at the WHEEL page: a single green triangle on that leg confirms it is down and locked (the red light is likely the other channel's sensor). This is the key reading when an indication looks wrong.

        Cockpit landing-gear interface
   ┌──────────────────────────────────────────────┐
   │  Hand (control)            Eye (indication)    │
   │  ──────────────            ─────────────────    │
   │  L/G lever, 2 positions    (1) indication panel │
   │   · UP / DOWN               (fed by LGCIU 1):    │
   │   · one continuous move     no light = up & locked
   │   · interlock locks DOWN    green ▿ = downlocked  │
   │     on the ground           red UNLK = not in posn │
   │   · red arrow              (2) WHEEL SD page       │
   │     (<750 ft + not locked   2 triangles/gear:      │
   │      + landing config)      left LGCIU 1, right 2; │
   │                             doors; L/G CTL; UPLOCK │
   │                            (3) E/WD warnings + memo │
   │                             FLT L/G DOWN (memo)     │
   └──────────────────────────────────────────────┘

2. The lever — two positions, one continuous movement, interlock

The lever has two positions (UP/DOWN) and signals both LGCIUs. Two operating disciplines. Per FCOM DSC-32-10-30:

The flight crew must always move the L/G lever in one continuous movement (i.e. with no stop between both positions).

Why no pause: stopping the lever mid-travel interrupts the continuous sequence the LGCIU is orchestrating and can leave a door or leg in an awkward intermediate state. Move it through in one stroke and let the sequence run to completion.

The interlock prevents an unsafe retraction. Per FCOM DSC-32-10-30:

An interlock mechanism prevents unsafe retraction by locking the lever in the DOWN position, when either: Both main landing gear bogies are compressed (aircraft on ground), or... The nose landing gear shock absorber is not fully extended (aircraft on ground), and the nose wheels are not in the center position.

This is the same mechanism as the baulk in article 04 — the FCOM calls it the interlock, the AMM calls it the baulk, one device: while the aircraft is still on the ground (bogies compressed, absorber not extended) it locks the lever at DOWN, preventing an inadvertent retraction that would settle the aircraft onto its bays. After lift-off the mechanism releases and UP becomes available.

3. Wheel braking on retraction — main versus nose

Per FCOM DSC-32-10-30:

During gear door opening, main... landing gear wheels are automatically braked by the normal braking system. The nose gear wheels are braked by a brake band in the gear bay.

The counter-intuitive point from the Overview: the main wheels are stopped electrically by the BSCU normal braking, the nose wheels by a mechanical brake band in the bay — because the nose wheel has no proper brake and is rubbed to a stop by a band before it enters the bay.

4. The red arrow — the last gear-up-landing alert

Per FCOM DSC-32-10-30:

The red arrow comes on when the aircraft is below 750 ft radio altimeter and the landing gear is not downlocked in landing configuration. Associated with the L/G GEAR NOT DOWN alert.

This is the cockpit-side last reminder against landing with the gear up — the same purpose as the GPWS TOO LOW GEAR (see LGCIU and Position Warning). The handling follows L/G GEAR NOT DOWN (see Gear Not Down or Not Locked).

5. The WHEEL SD page — reading the two triangles

Each gear is shown by two triangles. Per FCOM DSC-32-10-30:

The landing gear is indicated by two triangles for each gear. The left triangle is controlled by LGCIU 1, the right one by LGCIU 2.

Each triangle shows downlocked / in transit / retracted-uplocked / LGCIU failed; door indications show closed-and-locked / in transit / open. Two further cues: L/G CTL INDICATION triggers an ECAM alert if gear and lever positions disagree for more than 30 seconds; UPLOCK INDICATION flags L/G GEAR UPLOCK FAULT if the gear is downlocked but one or more uplocks remain in the closed position.

The same trust rule as the panel. Per FCOM DSC-32-10-30:

When the landing gear lever is down, one LGCIU locked down indication (one green triangle per gear) is sufficient to indicate that the landing gear is down and locked.

6. Auto-display and the FLT L/G DOWN memo

The WHEEL SD page auto-displays. Per FCOM DSC-32-10-30:

automatically displayed: On ground, before takeoff with engine running (flight phase 2). It disappears at engine T.O power application. In approach, at landing gear down selection or below 800 ft radio height (flight phases 7, 8, 9). It disappears at engine shutdown.

Note the two parallel triggers (an OR), not two versions of one number: the gear-down-selection trigger applies with the gear selected DOWN and downlocked, and the page is then held — the AMM adds the window for this trigger as below 10000 ft, held until the last engine stops (flight phase 9). The second trigger is below 800 ft radio height, a low-height backstop that brings the page up even if the gear has not been selected down. So 10000 ft is the window for the gear-down trigger and 800 ft is the low-height backstop — each governs its own branch, and the two agree.

The FLT L/G DOWN memo. Per FCOM DSC-32-10-30:

FLT L/G DOWN: This memo appears in green if the aircraft is operated in 'flight with landing gear down' configuration.

It reminds you that you are flying with the gear down (after a gravity extension, or with a gear that would not retract), and is associated with the related speed limit (MAX SPEED 200 after a gravity extension — see Gravity Extension).

[!warning]- Five misconceptions this article corrects (1) You do not need all green triangles to confirm a leg is locked — one green triangle per gear is sufficient (either of the two channels confirming downlock is credible). (2) The lever may not be moved in two stages — one continuous movement, or the sequence is interrupted. (3) A lever locked at DOWN on the ground is not a fault — it is the interlock/baulk preventing inadvertent retraction (bogies compressed / absorber not extended). (4) The red arrow does not mean a mechanical gear failure — it is the gear-up-landing alert (below 750 ft + landing config + not downlocked), associated with L/G GEAR NOT DOWN. (5) The nose wheels on retraction are not stopped by the braking system — the main wheels are (normal braking), but the nose wheels are stopped by a mechanical brake band in the bay.

Self-test

[!note]- Q1. What do the three indication-panel states mean, and how do you confirm a leg is locked if a UNLK will not extinguish on extension?

No light = up and locked; green ▿ = downlocked; red UNLK = not in the selected position. If a UNLK persists, look at the WHEEL page — a single green triangle on that leg is sufficient to confirm it is down and locked, because either of the two independent channels confirming downlock is credible. The red is likely the other channel's sensor.

[!note]- Q2. Why must the lever be moved in one continuous movement, and what direction does the interlock lock on the ground, protecting against what?

A pause mid-travel interrupts the continuous sequence the LGCIU is running and can leave a door or leg in an intermediate state. The interlock locks the lever at DOWN on the ground (bogies compressed / nose absorber not fully extended), preventing an inadvertent retraction that would settle the aircraft onto its bays. It is the same mechanism the AMM calls the baulk.

[!note]- Q3. On the WHEEL page, which LGCIU controls each triangle, and is one green triangle enough to confirm downlock?

The left triangle is controlled by LGCIU 1, the right by LGCIU 2. Yes — with the lever down, one green triangle per gear is sufficient to confirm the gear is down and locked.

[!note]- Q4. What three conditions light the red arrow, and what warning and GPWS call is it associated with?

Below 750 ft radio altitude, gear not downlocked, and in a landing configuration. It is associated with the L/G GEAR NOT DOWN alert and is the cockpit equivalent of the GPWS TOO LOW GEAR — both protect against a gear-up landing.

[!note]- Q5. On retraction, how are the main and nose wheels each stopped?

The main wheels are automatically braked by the normal braking system (BSCU); the nose wheels are stopped by a mechanical brake band in the gear bay, because the nose wheel has no proper brake.

Key takeaways

References

A330 specifics per FCOM DSC-32-10-30 (Controls and Indicators — three-state indication panel with the "one green triangle is sufficient" rule, two-position lever with continuous movement and interlock, main-vs-nose wheel braking on retraction, red-arrow conditions, the WHEEL page two-triangle reading with L/G CTL and UPLOCK cues, auto-display timing, FLT L/G DOWN memo). The WHEEL-page auto-display branches (gear-down below 10000 ft, held to engine stop, OR below 800 ft radio) are corroborated against AMM 32-61-00. The interface diagram is an integrative synthesis of the FCOM text. The information architecture behind the lights, the proximity sensors and warning generation are in LGCIU and Position Warning; the WHEEL page tyre-pressure section is in Tyre Pressure Indication; individual ECAM warning handling is in the ECAM Warning Family and Gear Not Down or Not Locked.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.