Alpha Floor and TOGA Lock

The angle-of-attack protection keeps the aircraft from stalling by working the surfaces: pull full aft and Normal Law holds the angle of attack between αPROT and αMAX. But holding off the stall is not the same as having the energy to fly away. If the engines are at idle and the aircraft is sinking, you can be not stalled and still bleeding energy with no flight path left to recover by pitch alone — and at that point the elevators cannot save you. Only thrust can.

Alpha floor is the one place on the A330 where the system adds thrust for you. When the angle of attack crosses the alpha-floor threshold, the autothrust drives the engines to TOGA — regardless of where the thrust levers are sitting, and regardless of whether the autothrust was even engaged. It is the energy backstop at the bottom of the low-energy protection chain, and it exists only in Normal Law. This article takes that chain apart: how alpha floor is triggered (two ways, not one), the five things it does at once, how TOGA thrust then locks and the single action that releases it, the availability window and the five inhibitions, and the "SPEED SPEED SPEED" alert that comes one step before.

One framing warning up front, because it governs everything else:

[!warning]- Alpha floor is a Normal-Law-only, low-speed protection — it is switched off in high-speed cruise, and that is not a fault.

Pilots often carry a mental model of alpha floor as a universal stall backstop that is always watching. It is not. It is inhibited above M 0.53, it is inhibited in some one-engine cases, it is inhibited below 100 ft on landing, and it disappears entirely the moment you leave Normal Law. Seeing no A.FLOOR capability in cruise is the designed state, not a malfunction. Treat alpha floor as a low-speed, low-level energy rescue — not a full-envelope safety net.

1. Where alpha floor sits — the low-energy chain

Alpha floor is not a single kick of thrust standing on its own. It is the middle link of a graded low-energy chain that escalates as energy falls: first an aural warning, then automatic thrust, then a thrust lock. Each stage intervenes harder than the last.

   ENERGY FALLING ──► the system intervenes progressively harder

  ┌──────────────────────────────────────────────────────────┐
  │ STAGE 1   LOW ENERGY AURAL ALERT  "SPEED SPEED SPEED"      │
  │           repeated every 5 s                               │  pure warning
  │           "pitch alone can no longer recover the           │  (no surface,
  │            flight path — add thrust"                       │   no thrust)
  │           only CONF 2 / 3 / FULL · 100–2 000 ft · Normal   │
  └───────────────────────────┬──────────────────────────────┘
                              │  ignored / decelerating further
                              ▼
  ┌──────────────────────────────────────────────────────────┐
  │ STAGE 2   ALPHA FLOOR fires → 5 events at once (§3)        │
  │           · A/THR activates (engaged or not)               │  automatic
  │           · A.FLOOR mode engages                           │  thrust
  │           · TOGA commanded (levers ignored)                │
  │           · FMA: A.FLOOR flashing amber box, line 1        │
  │           · EWD: A.FLOOR                                   │
  └───────────────────────────┬──────────────────────────────┘
                              │  aircraft accelerates, α falls
                              ▼  "leaves the alpha-floor conditions"
  ┌──────────────────────────────────────────────────────────┐
  │ STAGE 3   TOGA LK — TOGA thrust frozen and held            │
  │           FMA: TOGA LK flashing amber box, line 1 col 1    │  thrust held
  │           α is normal again, but thrust will NOT back off  │  until crew
  │           ONLY release: A/THR instinctive disconnect pb    │  acts
  └──────────────────────────────────────────────────────────┘

Three things to read off the chain before the detail:

1. It is one escalating system, not three independent features. The aural alert tries to make you fix the energy; if you do not, alpha floor fixes it; once fixed, TOGA LK keeps it fixed until you confirm a safe state.
2. The split between "can it fire" and "what it does" matters. Section 2 is the trigger logic; sections 3–4 are the consequence; section 5 is the availability logic — in many perfectly normal situations alpha floor is simply not armed.
3. TOGA LK is the back half of one event, not a separate protection. Alpha floor adds the thrust; TOGA LK stops it falling away once the angle of attack has recovered.

Who does what

Alpha floor is the hinge between two systems that otherwise stay apart: the flight-control protection brain (PRIM) and the autothrust (A/THR). The PRIM senses the angle of attack and owns the threshold; the A/THR owns the throttles. Alpha floor is where the first reaches across into the second.

2. The trigger — a threshold between αPROT and αMAX, reached two ways

2.1 Where the threshold lives

The alpha-floor threshold is not a fixed angle. It sits between the two angle-of-attack lines you already know from AoA protection. Per FCOM DSC-22_30-50-50:

ALPHA FLOOR avoids flying at low speed with a low thrust.

and the mechanism in the same passage:

ALPHA FLOOR automatically applies TOGA thrust if the aircraft angle of attack exceeds the ALPHA FLOOR threshold (between αprot and αmax) that depends on the aircraft configuration.

Put it on the angle-of-attack ladder: decelerate, the angle of attack rises, you reach αPROT first (high-AoA protection engages, the amber-and-black strip), a little higher you cross the alpha-floor threshold (TOGA is applied), and only at the top is αMAX (the hard ceiling you reach on full back stick). The flight-controls chapter is explicit that the two events come almost together. Per FCOM DSC-27-20-10-20:

Between αPROT and αMAX, the αfloor protection may automatically set go-around thrust. The αfloor will usually be triggered just after entering the αPROT, and go-around thrust will automatically be applied.

That "usually triggered just after entering αPROT" is the practical pilot intuition: in real life, entering the amber-and-black strip and the throttles slamming forward happen all but back-to-back.

How is the threshold computed? The flight-controls chapter names the computing authority and why the value moves. Per FCOM DSC-27-20-10-20:

Vα PROT, Vα MAX, and αfloor condition are mainly computed based on the AOA, and therefore they vary with configuration, weight and load factor.

and:

The αfloor activation logic is provided by the PRIM.

So the threshold is an angle-of-attack-derived value that shifts with configuration, weight and load factor, and the PRIM is the computer that owns the logic.

2.2 The second path — manoeuvre, not just deceleration

Most pilots remember only the "decelerate until the angle of attack reaches the threshold" path. There is a second, faster path: a hard pull at high attitude calls alpha floor straight out, before any slow deceleration. Per FCOM DSC-22_30-50-50:

Note: A.FLOOR is activated through the autothrust system, when: ‐ α is greater than a threshold depending on the aircraft configuration, the ground speed variation, and the difference between ground speed and air speed, or ‐ Sidestick deflection above 14 ° and the: • Pitch attitude is greater than 25 °, or • AOA protection active.

Two details are worth digging out of that note:

• The first path quietly carries wind information. The threshold depends not only on the angle of attack but on the ground-speed variation and the difference between ground speed and air speed — and ground speed minus airspeed is a wind component. The practical effect is that in windshear the threshold is reached earlier, which is exactly the case alpha floor exists to rescue (§6, scenario).
• The second path is the manoeuvre trigger: stick deflection beyond 14°, with either pitch attitude over 25° or AoA protection already active. In a violent escape pull, you do not have to wait for the angle of attack to creep up to the threshold — TOGA arrives early.

[!warning]- "Alpha floor only fires when I decelerate slowly into the threshold." Wrong — a hard pull at high attitude triggers it too.

Predict first: you haul the sidestick to do an avoidance pull at 30° nose-up, and the angle of attack has not yet reached the threshold. Does alpha floor fire? Yes. The second path (stick > 14° with attitude > 25°, or AoA protection active) is built precisely for the manoeuvre case — the aircraft is clearly about to need energy even though the slow-deceleration threshold has not been crossed. Remembering only the first path means understanding only half of alpha floor.

3. What alpha floor does — five events, bypassing the thrust levers

Once the condition is met, the system does five things together. Per FCOM DSC-22_30-50-50:

If A.FLOOR activates, all the following events occur: 1. The A/THR automatically activates, independently of the previous A/THR engagement status 2. The A.FLOOR mode of the A/THR engages 3. The A/THR commands TOGA thrust, regardless of the thrust lever positions 4. The FMA displays A.FLOOR with a flashing amber box on Line 1 of the "A/THR Messages and Modes" column 5. The EWD displays A.FLOOR

Events 1 and 3 are the teeth of the protection:

• Event 1 — "independently of the previous A/THR engagement status." You may have the autothrust off, flying the throttles entirely by hand — alpha floor still force-engages the A/THR and takes the throttles.
• Event 3 — "regardless of the thrust lever positions." The levers can be at IDLE while the thrust goes to TOGA. The levers and the actual thrust are decoupled. The FCTM's worked example states it plainly. Per FCTM AS-FG-10-2:

When the speed decreases, so that the angle-of-attack reaches the ALPHA FLOOR threshold, A/THR activates and orders TOGA thrust, despite the fact that the thrust levers are at IDLE.

In the A/THR mode table this is logged as a reversion that any starting mode falls into. Per FCOM DSC-22_30-50-50:

Whatever A/THR mode. The A/THR can be armed, active, or disconnected.

— armed, active, or disconnected, the mode reverts to A.FLOOR. There is no autothrust state from which alpha floor cannot reach you.

3.1 A third constraint it ignores — degraded navigation

There is a deeper layer of robustness that does not appear in the FCOM at all; it only surfaces in the autothrust engagement logic in the AMM. Normal A/THR engagement carries a hidden hard gate: the flight-guidance side must see two valid air-data/inertial reference units, and losing the second one drops the autopilot and flight director. Alpha floor steps over even that. Per AMM 22-31-00:

The Flight Guidance and Envelope (FGE) portion must receive two valid Air Data/Inertial Reference Units (ADIRU). When a second ADIRU is lost, the IR/ADR condition disengages the AP/FD. In alpha floor condition the A/THR is independent of the IR/ADR monitoring status.

What that means for the crew: imagine you have already lost a second ADIRU — the AP/FD have been dropped by the IR/ADR condition, and the normal A/THR engagement condition (two valid ADIRUs) is not satisfied. Enter the alpha-floor condition anyway, and the A/THR still force-engages and still commands TOGA. Stack this against events 1 and 3 and the picture is complete: alpha floor bypasses "the A/THR was not engaged," "where the levers are," and "navigation has degraded far enough to drop the AP/FD" — three constraints at once. That is why it is the most stubborn energy backstop on the aircraft: it is designed to deliver that one TOGA push even while much of the rest of the system is shedding capability.

The FMA annunciation has a precise meaning of its own. Per FCOM DSC-22_30-80-20, the conditions for the A.FLOOR box are:

A/THR is active and the engines apply maximum thrust, while A.FLOOR conditions are applicable.

4. TOGA LK — thrust frozen after the condition clears

This is the most easily confused point in the topic: A.FLOOR and TOGA LK are not two protections — they are the front and back halves of one event. Front half (A.FLOOR): the condition is live and TOGA is being applied automatically. Back half (TOGA LK): the condition has cleared, but TOGA is held rather than allowed to fall away. Per FCOM DSC-22_30-50-50:

If the aircraft leaves the ALPHA FLOOR conditions, the FMA displays TOGA LK with a flashing amber box on the first line of the first column. This indicates that the TOGA thrust is maintained.

The FMA chapter pins the word "locked" down to frozen thrust. Per FCOM DSC-22_30-80-20, the conditions for the TOGA LK box are:

A/THR is active and TOGA thrust is frozen (A.FLOOR conditions are no longer applicable).

Why lock it? The design logic is conservative with energy: alpha floor pulls you out of the low-energy state, the aircraft accelerates, and the angle of attack naturally falls back below the threshold. If thrust were dropped the instant the condition cleared, the energy you had just clawed back could collapse again. So TOGA is deliberately held until you confirm a safe state and release it yourself.

4.1 The single way out

Both the flight-controls chapter and the FCTM give exactly one release path. Per FCOM DSC-27-20-10-20:

To recover a normal flight condition, the αPROT should be exited by easing forward on the sidestick, as described above, and the αfloor should be cancelled by using the disconnect pushbutton on either thrust lever as soon as a safe speed is regained.

The FCTM is blunter — the only way to recover the thrust you want is to set the A/THR off. Per FCTM AS-FG-10-2:

TOGA thrust is maintained or locked. TOGA LK appears on the FMA to indicate that TOGA thrust is locked. The desired thrust can only be recovered by setting A/THR to off, with the instinctive disconnect pushbutton.

The FCTM also gives the technique for that disconnect, so the thrust does not jump. Per FCTM AS-FG-10-2, the recommended way to set A/THR off is to:

Return the thrust levers to approximately the current thrust setting, by observing the TLA symbol on the thrust gauge

then press the instinctive disconnect pushbutton and check AUTO FLT A/THR OFF on the ECAM with no annunciator in the first FMA column. Lead with the levers, then disconnect — otherwise the thrust steps to whatever the lever position commands.

  TOGA LK on FMA, safe speed regained
        │
        ▼
  ┌──────────────────────────────────────────────────────┐
  │ 1. Move thrust levers to ≈ current actual thrust       │  (read TLA
  │    (so thrust will not step on disconnect)             │   on gauge)
  │ 2. Press A/THR instinctive disconnect pushbutton       │
  │ 3. Check "AUTO FLT A/THR OFF" on ECAM, FMA col 1 clear │
  │ 4. Adjust thrust as required                           │
  └──────────────────────────────────────────────────────┘

There is a double-edged side effect to know. Per FCOM DSC-22_30-50-50:

CAUTION The A.FLOOR mode will disconnect, if the flight crew manually disconnects the A/THR.

The same pushbutton that releases TOGA LK will also kill A.FLOOR while it is still live and still saving you. That is why the release condition is always FCOM's "as soon as a safe speed is regained" — disconnect too early, while the alpha-floor condition still holds, and you have hand-cancelled the very TOGA that was rescuing you.

[!warning]- "Once it accelerates, TOGA will back off on its own." It will not — and pushing the levers forward does nothing.

Predict first: alpha floor rescues you, speed recovers to 150 kt, you touch nothing. What does the thrust do? It stays at TOGA — that is TOGA LK, and it holds until you press the A/THR instinctive disconnect pushbutton. Advancing the thrust levers from IDLE will not help: the levers are decoupled from the thrust. The only key is the instinctive disconnect.

5. The availability window and the five inhibitions

Alpha floor is not armed all the time. First the window. Per FCOM DSC-22_30-50-50:

ALPHA FLOOR is available from the lift-off to 100 ft RA in approach if the A/THR is available.

The 100 ft RA floor on landing is deliberate: in the flare you are meant to decelerate and raise the angle of attack, so a TOGA kick down low would be exactly wrong — alpha floor steps off at 100 ft (and that is also inhibition 2 below).

Now the five inhibitions, verbatim. Per FCOM DSC-22_30-50-50:

ALPHA FLOOR is inhibited if one of the following is applicable: ‐ A/THR is failed, or ‐ The aircraft altitude is below 100 ft during landing, or ‐ The aircraft speed is above M 0.53, or ‐ One engine is failed with the flaps extended or with Derated Takeoff selected, or ‐ AP/FD TCAS mode engages.

Reading each one for why:

• A/THR failed. Alpha floor works the throttles through the A/THR — lose that hand and there is no protection. The same point shows up in operator MEL entries: with the A/THR inoperative, all A/THR functions including ALPHA FLOOR protection are lost.
• Below 100 ft during landing. As above — no TOGA kick in the flare. This is the same boundary as the window's lower edge.
• Above M 0.53. Alpha floor is a low-speed protection — for approach, climb-out, windshear. In high-speed cruise the angle of attack is low and you should not be relying on it; M 0.53 is the "lights-off" line. Seeing nothing in cruise is normal.
• One engine failed with flaps extended or Derated Takeoff selected. On one engine in a low-speed, high-drag configuration you are already managing thrust and gradient against V2 by procedure; an unbidden TOGA kick would interfere with that management, so in these one-engine low-speed cases the protection stands down and hands thrust control back to the crew.
• AP/FD TCAS mode engaged. A TCAS RA needs precise vertical guidance; an alpha-floor TOGA push would corrupt the resolution trajectory. So TCAS takes priority (the exact, more nuanced logic is in §6).

[!warning]- "If I stall at high speed in cruise, alpha floor will catch me." It is switched off above M 0.53.

Predict first: cruising at M 0.78, a sudden large deceleration — does alpha floor add thrust? No (inhibited above M 0.53). What protects you up high is the surface side of the angle-of-attack / high-speed protections plus your own thrust input. Do not carry alpha floor into the cruise as a full-envelope talisman; it is a low-speed tool.

6. The TLA < 5° trap — disabling the protection without knowing it

The one-engine inhibition (number 4) hides a trap, because the system infers "engine failed" from thrust lever angle, and it can read two misaligned levers as a dead engine. Per FCOM DSC-22_30-50-50:

CAUTION The system may consider an engine as failed if the corresponding Thrust Lever Angle (TLA) is below 5° and another TLA is above 5°. The system may therefore inhibit ALPHA FLOOR. In manual thrust control, the flight crew should check that all the thrust levers are correctly aligned above 5° to avoid an undue inhibition of ALPHA FLOOR.

Work it through. Alpha floor has no direct "engine shut down" input for this test — it infers a failure from lever angle: "one lever near idle (< 5°), the other clearly working (> 5°) — probably an engine out." The problem is that if you are flying manual thrust with both engines healthy but the levers not set together (say one at 4°, one at 8°), the system mis-reads it as a one-engine failure and inhibits alpha floor along with it. So in the low-speed approach where you most need it, the protection can quietly vanish because of an unremarkable lever misalignment — and there is no dedicated annunciation telling you alpha floor is now gone.

The takeaway is a habit: in manual thrust, keep the levers aligned and both above 5°. That is not tidiness for its own sake — it is keeping an invisible, potentially life-saving protection alive.

7. TCAS RA — a more precise inhibition than "off"

Inhibition 5 is not a blunt "engaged = permanently off." It depends on where the thrust levers are. Per FCOM DSC-22_30-40-100:

When AP/FD TCAS mode is engaged, ALPHA FLOOR is temporarily inhibited: ‐ If all thrust levers are set to CLB detent when the RA is triggered, ALPHA FLOOR is inhibited while AP/FD TCAS mode is engaged. ‐ If at least one thrust lever is below the CLB detent when the RA is triggered, LVR CLB flashes on the FMA and ALPHA FLOOR is inhibited during 5 s, then: • If all thrust levers are set to the CLB detent, ALPHA FLOOR inhibition is maintained while AP/FD TCAS mode is engaged. • If at least one thrust lever remains below the CLB detent, ALPHA FLOOR is reactivated.

The one-line version: on a TCAS RA, levers in CLB → alpha floor stays inhibited (let TCAS guide); levers not in CLB → inhibited for 5 s with LVR CLB flashing, after which you either push to CLB and keep it inhibited, or alpha floor reactivates as the backstop. It is the compromise that lets TCAS guidance take priority without leaving you with no energy protection at all.

8. The front of the chain — "SPEED SPEED SPEED"

Five-or-so seconds before alpha floor, there is a pure-warning stage that touches neither surface nor throttle. Per FCOM DSC-27-20-10-20:

A low energy aural alert "SPEED SPEED SPEED" repeated every 5 s indicates to the pilot that the aircraft energy becomes lower than a threshold under which to recover a positive flight path angle through pitch control, the thrust must be increased.

The heart of it is "through pitch control… the thrust must be increased": at this energy, pulling no longer works — only thrust does. The alert exists to drag your hand from "pull a little more" to "add power." Its window is narrow. Per FCOM DSC-27-20-10-20:

It is available in configuration 2, 3 and full between 100 and 2 000 ft.

and it is computed by the PRIM from aircraft configuration, air-speed deceleration rate and flight path angle. The inhibitions, per FCOM DSC-27-20-10-20:

It is inhibited when: ‐ TOGA is selected ‐ Below 100 ft RA ‐ Above 2 000 ft RA ‐ Alpha floor or GPWS alert is triggered ‐ In alternate or direct law ‐ If both RA are failed

Reading them: landing configurations only (it is an approach protection); 100–2 000 ft (lower is too late, higher is not its case); silent once TOGA is selected (you are already at full thrust); silent once alpha floor or GPWS triggers (a higher protection has taken over — no duelling warnings); Normal Law only, like alpha floor; and gone if both radio altimeters fail, since it depends on RA for its window.

The FCOM quantifies how it leads alpha floor. Per FCOM DSC-27-20-10-20:

For example, if the aircraft decelerates at 1 kt/sec, and: ‐ The FPA is -3 °, the alert will trigger at approximately VLS -8, ‐ The FPA is -4 °, the alert will trigger at approximately VLS -2.

and its place in the chain. Per FCOM DSC-27-20-10-20:

The low energy aural alert is triggered during deceleration before alpha floor (unless alpha floor is triggered by stick deflection), the delay between the two alerts depends on deceleration rate.

Note the parenthesis: if alpha floor is fired by the manoeuvre path (§2.2), the aural alert may not come first — a sudden hard pull leaves no slow deceleration for it to lead. The FCTM gives the standard response. Per FCTM PR-AEP-MISC:

The "SPEED, SPEED, SPEED" aural alert announces a low energy situation. This situation requires a flight crew action to increase the energy.

and:

Increase the thrust or/and adjust the pitch depending on the situation, until the aural alert stops.

[!warning]- "SPEED SPEED SPEED is a stall or overspeed warning." It is neither — it is an energy warning, and the answer is thrust.

Predict first: it sounds — do you pull or add power? Add power ("through pitch control… the thrust must be increased"). It is not a stall warning (Normal Law will not let you stall) and not an overspeed warning; it is a low-energy cue telling you that the elevator can no longer recover the flight path and the throttles must. That is its mental difference from a stall warning.

9. Across an approach — the chain in motion

Six short scenes turn the static logic into a moving picture:

1. Slow deceleration on approach, "SPEED SPEED SPEED" sounds (CONF FULL, ~800 ft). Stage 1. Do not pull for altitude — per the FCTM, add thrust (adjust pitch as needed) until it stops. Get this right and it never reaches alpha floor.
2. Ignored, the angle of attack reaches the threshold, A.FLOOR fires. A.FLOOR appears in the flashing amber box on FMA line 1, the EWD shows A.FLOOR, the levers are still in your hand and unmoved while the thrust runs to TOGA. Let it work — fly the aircraft.
3. Accelerated, FMA shows TOGA LK. The angle of attack has dropped below the threshold and A.FLOOR has become TOGA LK — TOGA is locked. Pushing the levers forward does nothing. Once speed is back to a safe value, use the FCTM technique: levers to ≈ current thrust, then the instinctive disconnect pushbutton, and the lock releases smoothly.
4. Avoidance pull, 30° nose-up. This is the §2.2 manoeuvre path (stick > 14°, attitude > 25°). The angle of attack may not yet be at the threshold — alpha floor gives you TOGA early. This is the GPWS/windshear case where the protection extracts maximum performance. Per FCOM DSC-27-20-10-20: In the case of application of GPWS or windshear procedures, the aircraft protections provide maximum lift / maximum thrust / minimum drag. Therefore, CFIT escape maneuvers will be much more efficient.
5. Cruise at M 0.78, sudden large deceleration. Alpha floor does not fire (inhibited above M 0.53). Do not wait for it — at high speed it is your own thrust plus the surface side of the angle-of-attack protection. Once you drop out of Normal Law into Alternate Law, alpha floor and the low-energy alert both disappear entirely. Seeing no A.FLOOR is normal.
6. Manual thrust on approach, levers not aligned (4° and 8°). The system mis-reads a one-engine failure and inhibits alpha floor (§6), with no dedicated cue. Habit: keep both levers aligned above 5°. And if a TCAS RA arrives now with a lever below CLB, §7 applies — a 5 s inhibition with LVR CLB flashing.

Self-test

[!note]- Q1. Where is the alpha-floor threshold, and besides slow deceleration what else triggers it?

The threshold sits between αPROT and αMAX, varies with configuration, weight and load factor, and the activation logic is provided by the PRIM. It is "usually triggered just after entering αPROT," so it follows angle-of-attack protection almost immediately. There are two paths: (1) the angle of attack exceeds a threshold that also depends on ground-speed variation and the difference between ground speed and airspeed — i.e. it carries wind information, so it fires earlier in windshear; (2) sidestick deflection above 14° with pitch attitude above 25° or AoA protection already active — the manoeuvre path, which fires before any slow deceleration. Remembering only the first path is remembering half of it.

[!note]- Q2. List the five things alpha floor does, and name the two that give it teeth.

(1) The A/THR activates automatically, regardless of its previous engagement status; (2) the A.FLOOR mode engages; (3) the A/THR commands TOGA regardless of thrust lever position; (4) the FMA shows A.FLOOR in a flashing amber box on line 1; (5) the EWD shows A.FLOOR. The teeth are 1 and 3: you can have the autothrust off and the levers at IDLE, and it still force-engages and runs to TOGA — levers and thrust are decoupled. A deeper layer of robustness: in the alpha-floor condition the A/THR is independent of the IR/ADR monitoring status, so even with a second ADIRU lost (AP/FD dropped, the normal two-ADIRU A/THR gate unmet) it still engages and gives TOGA.

[!note]- Q3. What is TOGA LK, is it a separate protection, and how do you get out of it?

It is not a separate protection — it is the back half of the same event. A.FLOOR is "condition live, applying TOGA"; once the aircraft accelerates and leaves the alpha-floor conditions, the FMA shows TOGA LK, meaning TOGA thrust is frozen and held (so the just-recovered energy cannot collapse). The only way out: once a safe speed is regained, press the A/THR instinctive disconnect pushbutton on either thrust lever to set the A/THR off — "the desired thrust can only be recovered by setting A/THR to off." Advancing the levers does nothing; the FCTM technique is to first set the levers to ≈ current thrust, then disconnect, so the thrust does not step.

[!note]- Q4. What are the five inhibitions, and why M 0.53 and why the one-engine-with-flaps case?

Inhibited if: (1) A/THR failed; (2) below 100 ft during landing; (3) speed above M 0.53; (4) one engine failed with flaps extended or Derated Takeoff selected; (5) AP/FD TCAS mode engaged. M 0.53 because alpha floor is a low-speed protection — in high-speed cruise the angle of attack is low and you should not lean on it, so above M 0.53 it stands down (seeing nothing in cruise is normal). The one-engine-with-flaps case because in that low-speed, high-drag, single-engine state you are already managing thrust and gradient by procedure against V2; an unbidden TOGA kick would interfere, so the protection hands thrust control back to the crew.

[!note]- Q5. How can a thrust-lever angle below 5° disable alpha floor, and what is the low-energy alert?

Alpha floor infers a one-engine failure from thrust lever angle: if one TLA is below 5° while another is above 5°, it may judge an engine failed and inhibit alpha floor — with no dedicated annunciation. So in manual thrust, keep all levers aligned above 5° or you can lose the protection unawares. The low-energy alert is "SPEED SPEED SPEED" every 5 s — the front of the chain — meaning "pitch alone can no longer recover the flight path, increase thrust." It is available only in CONF 2/3/FULL, 100–2 000 ft, Normal Law, and is inhibited by TOGA selected, below 100 / above 2 000 ft RA, alpha floor or GPWS triggered, alternate/direct law, or both RAs failed. It comes immediately before alpha floor — unless alpha floor is triggered by stick deflection.

[!note]- Q6. Why is TOGA deliberately locked rather than allowed to back off when the condition clears?

Because the strategy is conservative with energy. Alpha floor pulls the aircraft out of a low-energy state; as it accelerates, the angle of attack falls back below the threshold. If thrust were dropped the instant the condition cleared, the energy just clawed back could collapse again. So TOGA is frozen (TOGA LK) and held until the crew confirms a safe state and releases it via the instinctive disconnect — "give more, don't take it away early." The lock is a feature, not a fault.

Key takeaways

References

Per FCOM DSC-22_30-50-50 (ALPHA FLOOR — definition; threshold between αprot and αmax; two-path activation note; the five events on activation; A/THR mode reversion to A.FLOOR; TOGA LK on leaving the conditions; CAUTION that manual A/THR disconnect also drops A.FLOOR; availability lift-off to 100 ft RA; the five inhibitions; TLA < 5° CAUTION). Per FCOM DSC-27-20-10-20 (relationship of alpha floor to αPROT — "usually triggered just after entering αPROT"; threshold computed by the PRIM and varying with configuration/weight/load factor; the only cancel path via the disconnect pushbutton; the GPWS/windshear "maximum lift / maximum thrust / minimum drag" statement; the full LOW ENERGY AURAL ALERT passage — meaning, CONF/altitude window, inhibitions, VLS example, computed by PRIM, position before alpha floor). Per FCOM DSC-22_30-40-100 (AP/FD TCAS consequence on ALPHA FLOOR — CLB-detent cases, 5 s, LVR CLB). Per FCOM DSC-22_30-80-20 (FMA display conditions for A.FLOOR and TOGA LK — active + maximum thrust; TOGA frozen). Per FCTM AS-FG-10-2 (worked example — levers at IDLE while TOGA commanded; "desired thrust can only be recovered by setting A/THR to off"; the recommended disconnect technique of returning the levers to current thrust before pressing the instinctive disconnect). Per FCTM PR-AEP-MISC (low-energy recovery — increase thrust and/or adjust pitch until the alert stops). Per AMM 22-31-00 (A/THR engagement logic — in the alpha-floor condition the A/THR is independent of the IR/ADR monitoring status). Operator MEL entries make the same point that an inoperative A/THR leaves ALPHA FLOOR protection inoperative.

Design-rationale statements presented as interpretation rather than verbatim manual text — that TOGA is locked specifically to stop the just-recovered energy collapsing; that the ground-speed/airspeed term amounts to wind information and so triggers earlier in windshear; that M 0.53 marks the low-speed-protection cut-off; and that the one-engine-with-flaps inhibition exists to avoid interfering with crew thrust/gradient management — are integrative synthesis built on the cited facts, not direct manual quotations.

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.