A320 Alpha Floor and A/THR Protection Loss: The 15-Second Rule, TOGA LK Cancellation, and the On-Ground Reset
Press to disconnect. Hold to regret.
Fifteen seconds. That is all it takes.
Hold the A/THR instinctive disconnect pushbutton one moment too long during an upset - trying to silence audio chatter, trying to buy quiet, trying to take control - and you have permanently disabled the autothrust system for the remainder of the flight. Alpha Floor is gone with it. Reset is an on-ground, before-taxi action only per the QRH. Not a mid-flight recovery. Not something you fix by pressing another button. On the ground. Before taxi. That is the reset window.
Most pilots have pressed the instinctive disconnect pushbutton thousands of times without ever knowing that holding it too long strips a critical safety net for the rest of the flight. The button is honest about what it does in the moment. It is quiet about the price of holding it too long. This page names the price, walks the mechanism, and cites the FCOM, FCTM, AFM, and QRH sections that carry the authority.
This is Spoke 3 of the Auto Flight Foundation Series. Spoke 1 walked the Auto Flight architecture. Spoke 2 walked the AP/FD modes and the go-around trigger. Spoke 3 closes the arc with the A/THR system, Alpha Floor, and the two operational traps examiners specifically probe: the 𝗧𝗢𝗚𝗔 𝗟𝗞 levers-are-decorations trap and the 𝟭𝟱-𝘀𝗲𝗰𝗼𝗻𝗱 permanent-disconnect trap. The full architectural context sits in the Foundation Guide.
Alpha Floor, A/THR, and the Traps Examiners Probe
What is the A320 15-second rule on the instinctive disconnect pushbutton?
If the flight crew pushes and holds one instinctive disconnect pushbutton for more than 15 seconds, the A/THR system is disconnected for the remainder of the flight. All A/THR functions, including Alpha Floor, are lost and can be recovered only at the next FMGC power-up on ground.
Hold > 15 seconds → 𝗔/𝗧𝗛𝗥 𝗢𝗙𝗙 for the remainder of the flight.
All A/THR functions lost, 𝗔𝗹𝗽𝗵𝗮 𝗙𝗹𝗼𝗼𝗿 𝗹𝗼𝘀𝘁 with it.
Recoverable only at the next FMGC power-up 𝗼𝗻 𝗴𝗿𝗼𝘂𝗻𝗱, 𝗯𝗲𝗳𝗼𝗿𝗲 𝘁𝗮𝘅𝗶.
Reset is an on-ground, before-taxi action only per the QRH. There is no mid-flight recovery path.
References: WZZ A320-A321 FCOM DSC-22_30-90 Autothrust p. 8/16; A320 QRH ABN-02 System Reset Table AUTO FLT A/THR OFF.
What triggers Alpha Floor on the A320?
Alpha Floor is activated through the A/THR system by 𝘁𝘄𝗼 𝗽𝘂𝗯𝗹𝗶𝘀𝗵𝗲𝗱 𝗿𝗼𝘂𝘁𝗲𝘀. Both are FCOM-defined; both are examinable.
Route 1 · AoA Threshold
Angle of attack > the alpha-floor threshold.
The FAC sends the trigger when AoA is above a predetermined threshold that is a 𝗳𝘂𝗻𝗰𝘁𝗶𝗼𝗻 𝗼𝗳 𝗰𝗼𝗻𝗳𝗶𝗴𝘂𝗿𝗮𝘁𝗶𝗼𝗻. In 𝗖𝗢𝗡𝗙 𝟯 and 𝗖𝗢𝗡𝗙 𝗙𝗨𝗟𝗟, the threshold decreases as a function of aircraft deceleration rate.
Route 2 · Sidestick Deflection
Sidestick deflection > 14° nose up 𝘄𝗶𝘁𝗵 either pitch attitude protection or angle-of-attack protection active.
Full aft sidestick is part of windshear escape technique. Under the two protection conditions above, sidestick input activates Alpha Floor.
References: WZZ A320-A321 FCOM DSC-22_40-30 Flight Envelope Function p. 3/4; A320 FCTM SI-010 Adverse Weather p. 13/16.
How does A320 Alpha Floor command TOGA thrust?
Alpha Floor protection automatically sets 𝗧𝗢𝗚𝗔 thrust when the aircraft reaches a very high angle of attack. The FAC generates the signal that triggers alpha-floor mode. This sets TOGA thrust on the engines 𝗿𝗲𝗴𝗮𝗿𝗱𝗹𝗲𝘀𝘀 𝗼𝗳 𝘁𝗵𝗿𝘂𝘀𝘁 𝗹𝗲𝘃𝗲𝗿 𝗽𝗼𝘀𝗶𝘁𝗶𝗼𝗻.
References: WZZ A320-A321 FCOM DSC-22_40-30 Flight Envelope Function p. 3/4; DSC-22_30-90 Autothrust pp. 11/16-12/16.
Under what conditions is A320 Alpha Floor lost or inhibited?
Alpha Floor loss and inhibit conditions are 𝗱𝗶𝘀𝘁𝗶𝗻𝗰𝘁 categories in the FCOM. Lost means the function is unavailable; inhibited means the function is suppressed by another active mode or condition.
The FCTM adds a 𝗱𝘂𝗮𝗹 𝗙𝗠𝗚𝗖 𝗻𝘂𝗮𝗻𝗰𝗲: dual FMGC failure disconnects AP/FD and A/THR, with possible recovery of AP and A/THR if flight guidance parts are still available.
References: WZZ A320-A321 FCOM DSC-22_40-30 Flight Envelope Function p. 4/4; A320 FCTM AO-022 FMGC Failure p. 1/2.
How is TOGA LK cancelled after an Alpha Floor event?
The FCTM is explicit on the cancellation. 𝗧𝗢𝗚𝗔 𝗟𝗞 can only be cancelled by setting A/THR OFF with the 𝗶𝗻𝘀𝘁𝗶𝗻𝗰𝘁𝗶𝘃𝗲 𝗱𝗶𝘀𝗰𝗼𝗻𝗻𝗲𝗰𝘁 pushbutton. After cancellation, thrust is recovered 𝗺𝗮𝗻𝘂𝗮𝗹𝗹𝘆 according to lever position. There is no universal three-step recovery sequence the manuals teach.
General FCTM Cancellation
Applies below 1,000 ft or outside CAT II/III conditions.
- 1. Disconnect A/THR via instinctive disconnect button
- 2. Thrust follows lever position from that point
CAT II/III Above 1,000 ft (AFM)
Distinct procedure per the AFM:
- 1. Check speed
- 2. Disconnect
- 3. Re-engage autothrust mode
References: A320 FCTM OP-030 TOGA LK Cancellation; A320 AFM ABN-22-CATII and ABN-22-CATIIIDH.
How is A/THR reset after the 15-second permanent disconnect?
Reset is an 𝗼𝗻-𝗴𝗿𝗼𝘂𝗻𝗱, 𝗯𝗲𝗳𝗼𝗿𝗲-𝘁𝗮𝘅𝗶 action only. There is no in-flight recovery path. The QRH gives two procedural branches depending on engine state at reset time.
Branch A · No Engine Running
- 1. Press FCU A/THR pushbutton to re-engage A/THR
- 2. Press A/THR instinctive disconnect pushbutton
Branch B · At Least One Engine Running
- 1. Apply external power or APU generator power
- 2. Set ENG MASTER OFF for running engines
- 3. Press FCU A/THR pushbutton to re-engage A/THR
- 4. Press A/THR instinctive disconnect pushbutton
Both branches restore A/THR and Alpha Floor availability for the next departure. 𝗡𝗲𝗶𝘁𝗵𝗲𝗿 𝗯𝗿𝗮𝗻𝗰𝗵 𝘄𝗼𝗿𝗸𝘀 𝗶𝗻 𝗳𝗹𝗶𝗴𝗵𝘁.
Reference: A320 QRH ABN-02 System Reset Table AUTO FLT A/THR OFF, 02.02D.
What is the SPEED SPEED SPEED low-energy warning envelope?
The 𝗹𝗼𝘄-𝗲𝗻𝗲𝗿𝗴𝘆 𝗮𝘂𝗿𝗮𝗹 𝗮𝗹𝗲𝗿𝘁 is computed by the FACs using real-time flight path angle, deceleration trends, and flap and slat configuration. Its availability and inhibit envelope is FCOM-published in full.
Available In
- • CONF 2
- • CONF 3
- • CONF FULL
Inhibited When
- • Below 100 ft RA
- • Above 2,000 ft RA
- • TOGA selected
- • Alpha Floor or GPWS alert triggered
- • Alternate or direct law
- • Both radio altimeters failed
The pilot's immediate action when the warning sounds is to 𝗮𝗱𝘃𝗮𝗻𝗰𝗲 𝘁𝗵𝗲 𝘁𝗵𝗿𝘂𝘀𝘁 𝗹𝗲𝘃𝗲𝗿𝘀 𝗽𝗿𝗼𝗺𝗽𝘁𝗹𝘆.
Reference: WZZ A320-A321 FCOM DSC-22_40-30 Flight Envelope Function p. 4/4.
Primary Documentation
Every citation on this page is drawn from one of the following primary sources. Wizz Air operators should consult the WZZ-specific FCOM revision (653645391-WZZ-FCOM-19May2021.pdf) where noted. Other operators consult the equivalent fleet-specific revision.
- [FCOM] §DSC-22_30-90, Autothrust (Wizz Air rev. 19 May 2021) - 15-second rule, TOGA thrust command
- [FCOM] §DSC-22_30-100, Flight Mode Annunciator (FMA)
- [FCOM] §DSC-22_40-30, Flight Envelope Function - Alpha Floor triggers, thresholds, loss/inhibit conditions, SPEED SPEED SPEED envelope
- [FCTM] §OP-030, A/THR Cancellation and TOGA LK Cancellation (Issue 18 MAR 15)
- [FCTM] §SI-010, Adverse Weather - windshear escape technique, sidestick as Alpha Floor route
- [FCTM] §AO-022, FMGC Failure - dual FMGC recovery nuance
- [AFM] §ABN-22-CATII, CAT II Alpha Floor procedure above 1,000 ft
- [AFM] §ABN-22-CATIIIDH, CAT IIIDH Alpha Floor procedure above 1,000 ft
- [QRH] §ABN-02, System Reset Table AUTO FLT A/THR OFF, 02.02D - on-ground before-taxi reset (Branches A and B)
