ALPHA PROT/FLOOR/MAX
 

Hi everyone,
I know that there are some posts on this but I just would like to check all these:

Alpha floor is a protection and thrust goes to TOGA.
At alpha max (if you reach it :)), it will remain like this but when you will leave the stick, it will go towards Alpha protection and give the alpha floor.

But is the Alpha prot basically where Alpha floor arms? Or does alpha floor come in Alpha protection?

Is there something for take-off? I had read something with 5 seconds...

Alpha protection: Around 15 degrees AoA
Alpha Max: Around 18 degrees AoA
And at which angle does the alpha floor bring you?

Please clear me in these doubts!

Thanks

Go to smartcockpit.com, pick any of the FBW Buses system manuals and download the Flight Controls chapter. Your questions will be answered in fairly good detail.

Hi AF330,

it works like this.

You fly level, with stick released, and set throttles to idle. The aircraft will start decelerating toward speed Valpha prot (the yellow band). At Vaprot the low speed protection activates, and in order not to go any slower, the aircraft will pitch down to maintain Vaprot.

If you then pull on the stick and raise the nose, the speed will decay down to V alpha max (the red band). This means you will override the AlphaProt logic and fly slower than V alpha prot. The aircraft will keep descending, as you do not have a sufficient thrust to maintain level flight, but at speed V aplha max.

Actually, no. Because you asked for the aircraft to go upwards with your side stick command, a few moments before reaching V alpha max the A/THR system will command full thrust, irrespective of throttle levers position. This is called the A.FLOOR function of the autothrust system. Unless it is disabled beforehand by a specific trick, it will give you full power from the engines anytime the speeds gets too low (just above Valpha max).

So, eventually you will be climbing after all, with TOGA thrust and at speed V alpha max - provided you keep pulling on the stick. If you release the stick then, your override of AlphaProt function will cease to exist, and the AlphaProt function will lower the nose just a little in order to accelerate twards Valphaprot (the top of yellow band). When Valpha prot is regained, with released stick the aircraft will keep this speed, whilst climbing. The climb is the result of excess energy provided by the TOGA thrust from the engines.

I know this does not really answer all the questions you asked, but I would like to suggest you digest the above first, before going any deeper.

Sounds good?

Cheers,
FD.

Hi FlightDetent!

Thanks a lot for your great post! Yes, I had to read it 10 times to understand it! Yes, lot's of questions, like - I am sure- you had expected!
Well, this is what I have understood:

- When you are at level and you decrease the speed, if it reaches alpha protection, the plane will pitch down to get back speed.

QUESTIONS AT LEVEL

1) At which speed will it fly? The upper limit of Alpha protection?
2) But what if you had entered a speed in the FCU, and that speed was bellow VLS, will the plane maintain that speed or the alpha protection one?
3) The plane will go down, but what happens if you had your altitude managed?
4)Will "that" speed be managed by pitch?

- When you pull your stick, the plane will reach Alpha max, but Alpha floor will give max TOGA, till we leave the stick where alpha protection will pitch down and maintain the upper speed of alpha protection.

QUESTIONS GOING UP:

1) If we have climbed, I imagine that our altitude was not managed, or not even selected (open climb), the altitude function has disconnected, am I right? If yes, no questions about altitude!
1) Same question, will it maintain that speed by pitch?
2) What if we had entered a speed in the FCU? Will it still fly that one?

QUESTIONS WITH AN EXAMPLE

We are flying A320 and here are our waypoints:

-AGOPA: FL80- 220 knots
-LORNI: FL60- 210 knots
-MOPAR: FL50- 205 knots
-MANOX: FL30- 180 knots

We are at AGOPA, FL80 entered in the FCU, speed managed.
We forget do enter FL29 managed in the FCU, speed reaches 185 knots, and hits alpha protection and pitch goes down to regain speed...

1) At which speed will the plane fly?
2) Will it then leave our managed speed? Or still try to reach it?
3) At which altitude will it stabilize? Will it leave the managed altitude?

EXTRA QUESTIONS

I just would like a approximative number for these questions: (A320- A330)

1) What is generally a take-off angle?
2) A climb angle?
3) A cruise angle?

See what I read!
"Pitch during descent is only slighty negative e.g. at low altitude (e.g. 5000ft) at 64500kgs and 250kts the rate of descent is 1660ft/min which results in a pitch attitude of -0.6deg
At 214kts (approx green dot) the pitch attitude is +2.3deg during an idle descent!"

4) A descent angle?
5) After green dot angle?
6) Rotation altitude?

EXTRA QUESTIONS PART 2

1) Why during take-off the Alpha protection and alpha max is equal for 5 seconds?

QUESTION WITH A SADLY CRASH:

1) Why did AF447 stall? Didn't alpha floor react? Or was it too late?

Thanks a lot Flight Detent!
Thanks to clear me on these questions (very important for me!)...

With my kind regards,
AF330

AF330,

I ommited one very important fact in the first post for you. Everything I tried to describe was for a situation, where the guidance (the flight director) is completely off. So no ALT mode, or selecting speed on FCU.

Cheers,
FD.

Yes you are right flight detent. But could you please give me an approximation for the angle? At which angle does alpha protection come, at which angle does alpha max come? Thanks and regards

Let me give a try. :ooh: I may need to be quite picky with terminology, in order not to confuse one thing for another.

Rephrase needed: If you fly level and select thrust idle, the aircraft will initially maintain altitude but obviously deccelerate. Once the speed gets as low as V alpha prot (the top of the amber band), the alpha protection activates and will pitch nose down as necessary to maintain this Valphaprot.

1) Yes, see above.
2) Forget VLS this time, that's for Autothrust. We assume A/THR is off.
3) in my scenario, as the aircraft is not able to maintan level due too little thrust, the activation of alpha prot (nose down command) will disregardt the "ALT HOLD".
4) Yes, the aircraft will pitch up or down to maintaint V alphaprot.

Fair. Note that TOGA is commanded by the A.FLOOR feature, the max thrust will remain selected irrespective of stick position.

1) Your use of words "managed" and "selected" seem to indicate a different meaning to them compared to what I am used to. But my example assumes no altitude functions connected in a first place. :ok:
1) Yes, the alpha prot function, unless overriden by push/pull on the stick, will always adjust pitch so that aircraft will not fly slower than Valpha prot (top of the amber band). This may cause increase of descent (e.g. with thrust at idle), or a reduction in climb (e.g. with TOGA). The resulting trajectory will always depend on how much thrust is available from the engines in any particular moment.
2) See above, FCU speed selection is for guidance modes of autopilot and/or autothrust. I assume none are used.

From my point of view, the example you give involves interaction of speed protection function with altitude guidance, speed orders and, more over, the flight navigation computer's vertical features. To explain properly, we'll end up writing full FCOM. I'll need to pass. :bored:
Still
2) see above. The alpha prot will, at any time, reduce the pitch so that speed never goes below Valpha prot (top of amber band). Irrespective of any FCU or FMS settings. The only way to not pitch down is to pull on the stick, and override alpha prot. Then the speed would most likely drop all the way to V aplha max (top of the red band) at which point the alpha max protection will reduce the pitch to maintain V aplha max. This cannot be overriden.
3) Unless some action is taken, the unavoidable final altitude will be AGL=0. (joke, but true).


I assume by "angle" you mean pitch. My best guess for A320:
1) 13-18 deg nose up. Depends on speed / weight.
2) 3 to 12 deg nose up. Depends on speed / weight / altitude.
3) 1,5 to 3 deg nose up. Depends on speed / weight / altitude.
4) 3 deg up to 4 deg nose down. Depends on speed / weight / altitude.
5) Question not understood.
6) Likewise.

That is the way the software is designed. Probably to allow for dynamics of takeoff itself.

Very simplified: The sensors were providing erratic information. In such case, the protections were de-activated by internal logic.

Take care,
FD.

Oh!!!! Great!!!!!!!!! Thanks a lot Flight Detent!!!!! You are simply great!!!!!!!
I thought that when someone will read the size of my question, he won't even try to answer it!!!!!!!

Ok, less questions this time! But I am really getting it...

1) Is all the alpha stuff related to AoA or pitch?
2) What is the difference between pitch and AoA?

3) Could you just answer my question with angles with the AoA?
I had read something with 33 degrees, 45 degrees...
At what angle (pitch and AoA if possible!) does alpha protection come? alpha max?

4) Will that alpha protection speed controlled by our last lever position? (I don't think it will control it with TOGA!!!!) maybe climb ( if we were in A/THR) or IDLE...

5) Ok so basically you have to do something, and to remove alpha protection, or you put back the autopilot and everything in managed mode (so no problem!) or you try to take speed (pitch down or throttle..)

Thanks a lot Flight Detent! You really have helped me! Once again:
THANK YOU!

Take care,
With my kind regards,
AF330

You can tell your angle of attack with the FPV (bird) on. It's the angular difference between the 'bird' and the airplane symbol (pitch attitude) on your PFD. Hope that helps.

Thanks yardman...


1) So is the AoA between the chord line and the relative wind?
2) So I imagine that the alpha stuff is related to AoA...
3) But I just saw a video where they had reached alpha max and TOGA THRUST came, and brought them at 220 knots and then the video finished. But will the plane go to alpha protection speed by pitch? Well it's what I thought...
4) Is that speed, i imagine the alpha protection one, controlled by our last lever position (with pitch of course...)?
5) To remove alpha protection, you need to take speed by yourself, am I right?
6) Could you please give me the angles for AoA, and at which angle does alpha protection and max happen? ( pitch and AoA, if possible!)

Thanks a lot Flight detent and yardman!

FCOM:

Alpha-floor protection automatically sets the thrust at TOGA thrust, when the aircraft reaches a very high angle of attack.
The Flight Augmentation Computer (FAC) generates the signal that triggers the alpha-floor mode. This, in turn, sets TOGA thrust on the engines, regardless of the thrust lever positions (Refer to DSC-22_30-90 A/THR Modes - General).
The FAC sends this signal when:
‐ The angle of attack is above a predetermined threshold, that is a function of the configuration.

Once again, thanks Flight Detent!
But I think that I have understood that part...

Ok, let me explain myself:
We have our thrust IDLE, autopilot off, we reach alpha protection, and the plane pitches to maintain the alpha protection speed. But then we pull on the stick and the plane reaches alpha max, and alpha floor gives you full TOGA thrust. We release the stick and the plane stops at 220 knots, it then goes back to alpha protection speed, by the speed controlled by thrust. Then it maintains that by pitch.

1) Am I right till here?

Well, I hope...
My question, with which thrust levers is the alpha protection speed controlled with pitch? Is it IDLE, because we were in IDLE?

Same question:

We have our thrust CLIMB, autopilot off, we reach alpha protection, and the plane pitches to maintain the alpha protection speed. But then we pull on the stick and the plane reaches alpha max, and alpha floor gives you full TOGA thrust. We release the stick and the plane stops at 220 knots, it then goes back to alpha protection speed, by the speed controlled by thrust. Then it maintains that by pitch. My question, with which thrust levers is the alpha protection speed controlled with pitch? Is it CLIMB, because we were in CLIMB?

PS: Could anyone give me the angles at AoA? Rotation, climb, cruise, descent, alpha prot, alpha max...

Thanks a lot,
AF330

Well, let's say that I want to know which amount of thrust will be given? If our thrust levers WERE in IDLE, will it give IDLE thrust and maintain tge alpha protection speed with thrust IDLE+ pitch. Am I right?

Thanks

Ok, I have more or less got the concept. But could anyone give me this answer:
Alpha floor speed= alpha protection-.....knots.

So it will give alpha protection is from a "speed" to .....knots after that speed, alpha floor gives you TOGA thrust.

PS: for A320- A330
Thanks

I honestly have no idea what you're asking.

Hi FD,

You had said that at Vprot, the plane pitches down and maintains Vprot.
Vfloor is a function of A/THR. A/THR will never go below VLS.
So what is maintaining Vprot? Or does it simply pitch down to take back speed (and doesn't manage Vprot).
Or do the FAC send signals to the FADEC system and the other F-CTL? Does it manage Vprot by speed mode or thrust mode?

Thanks

It might help you to think of the thrust and pitch separately.

1)with low thrust, you let speed decay to Vprot. Then aircraft pitches down to maintain Vprot. Then you pull stick back and it allows you to go to V.a.max, but no lower. You release the stick again and it pitches down to accelerate to and maintain Vprot.

2) At some stage between Vprot and V.a.max, you get A.floor. This only does one thing. Orders TOGA from the engines which remains until you remove the thrust lock by pushing the instinctive disconnect. The position of the levers has no effect on the thrust at this stage. Even if you move them up and down, the thrust from the engines is locked at TOGA. This is not an autothrust function and there is no speed mode.

Thanks a lot!

So to maintain Vprot, FAC's send signals to the other F-CTL (to pitch down....etc) and also directly to FADEC? FAC's will basically do what A/THR does?

I understood your thing. But you say "to maintain Vprot"
When the plane pitches down, it can take speed. So if it is maintaining Vprot, something has to command.

So what is controlling speed at Vprot?

Thanks

at the stage it is maintaining vprot, it will do so by pushing nose down. This function is commanded by whichever computer is controlling the elevators and THS (Normally ELAC2 but redundency provided by ELAC1, SEC2, SEC1). As soon as there is enough thrust to exceed V.prot, it will maintain 1G as it is still in normal law... where zero sidestick commands 1G. this means if you get A.floor and leave the stick alone, you will accelerate (Rapidly) while maintaining 1G (and a level or slightly nose down attitude i imagine)

the FAC (there are 2 of them) monitors angle of attack and simply sends the message for TOGA... not sure if it sends it directly to the FADECs or through some intermediary...

If you maintain full back stick with A.floor, the plane will use pitch (Commanded by ELAC2) to keep V.a.max, pulling the nose up just as much as it can without letting the speed drop below V.a.max. The plane then climbs like a homesick angel.

The thrust is commanded to TOGA by the A.floor function of the FACs... when you are no longer in A.floor, this changes to TOGA LOCK... the only difference between the two is that you can get out of TOGA LOCK by pushing the instinctive disconnect, then take back manual control of the thrust, and re engage autothrust if you so desire In A.FLOOR you cannot get out of TOGA until the conditions (AoA) are no longer met for A.floor.

complicated i know....

Thanks,

1) Didn't reaaly get the 1G thing, could you explain please?

2) Ok, so Vprot is managed by ELAC. They know Vprot, they know the plane's IAS. Am I right or is it the FAC's who send signals of pitch to ELAc's?
It would mean that FAC's know Vprot, the IAS of the plane and it's attitude. It can then send signals of pitch to ELAC's

3) Ok Vfloor = managed by FAC's
Right?

4) TOGA LOCK = Given by A/THR
So once outside Alpha floor range, FAC's send signals to A/THR to give TOGA
Right?

Thanks

1. If everything is normal, the stick commands a g loading... 1g is normal gravity, 0g is weightless, 2g is pulling back real hard. with the stick neutral, the plane maintains 1g.

2. If everything is normal, elac2 gives the orders to the elevators to maintain vprot if the thrust is insufficient. Fac has nothing to do with it. elac knows v.prot.

3. Actually is A.floor... not a speed, but an angle of attack. Calculated by the Facs, yes.

4. The autothrust is not on. in fact it will even disengage at A.floor if it was on. the TOGA command is sent straight to the engine . Autothrust is off throughout the whole thing... just the fac tells the engines to hit toga power and stay there.

helping?

Yes! Thanks a lot!

So in normal law:

Vprot calculated and mainatained with ELAC.
Alpha floor range calculated and managed with FAC's till....
we exit the range: TOGA LCK.

1) Right?

2) But do at least FAC's send a signal to ELAC to tell him that it has to do something because we are at Vprot? Or do FAC's only come when we hit Alpha Floor?

Thanks a lot!

Good night...

haha i am really having to read the book in depth to get clear on all this now!

Firstly I must apologise for an error on point 4... you were correct and I was completely wrong, the thrust going to TOGA at A.floor is in fact an autothrust function!

Quote from FCOM DSC-22-30-90-A/THR ACTIVATION
"When ALPHA FLOOR is activated, regardless of the initial status of A/THR and the position of the thrust levers, the A/THR activates."


Next, the FACs do talk to the ELACs.
Quoting FCOM DSC-22-40-10-GENERAL
"Each FAC interfaces with the elevator aileron computers (ELACs) when the APs are disengaged, or with the FMGS when at least one AP is engaged."

Next, the book is slightly unclear whether these FAC calculated speeds (V.a.prot and V.a.max) are sent to the ELAC for use... it seems to suggest not, but i am certainly unaware of any capability of the ELACs to calculate these speeds themselves.
Quote from FCOM PRO-SUP-10-PROTECTION SPEEDS.
"Vα PROT, Vα MAX and VSW are computed by the FAC, based on aerodynamic data. They are only used for display on the PFD, and not for flight control protection (the activation of the protections is computed by the ELAC)."

More on A.floor, Quote from FCOM DSC-22-40-30 ALPHA FLOOR PROTECTION
"The FAC sends this signal (for A.floor) when :‐The angle of attack is above a predetermined threshold, that is a function of the configuration.‐In CONF3 and CONF FULL, this threshold decreases as a function of the aircraft deceleration rate (down to – 3 °)."

does that go some way to answering your questions?

Also I had a look today at the pitch attitude on the PFD in a moderately loaded A320. Cruise about 2deg up. Steep descent (High altitude, idle thrust, no speedbrake) 1deg nose down. Approach with flaps full, 3deg up.

Ok...so more questions now!

1) If we hit Vfloor, A/THR gives TOGA. Can we exit leave A/THR at Vfloor (by pressing red button on levers e.g)?

2) So how does it happen? FAC knows Vfloor. FAC sends a signal to A/THR to give TOGA?

3) Well...confused for Vprot....

What maintains Vprot???? Is it FAC or ELAC? Your F-COM says:
" and not for flight control protection (the activation of the protections is computed by the ELAC)."

It's pretty confusing. It says that FAC only displays Vprot...etc. So just 1 question here:

Option 1: ELAC knows Vprot. It knows it's IAS, it knows it's attitude --> No need of FAC's. ELAC's are managing Vprot.
Option 2: ELAC knows nothing (of course, it does but does not take any decision itself), FAC knows Vprot, our IAS and the attitude --> It sends to ELAC pitch command to maintain Vprot.

Your F-COM tends to say that ELAC do it alone. Of course, FAC's do other things such as stoping trim at Vprot. (Normal Law)
What do you think? (Option 1 or 2?)

Thanks a lot!

1) Don't understand your question. What do you mean by "Can we exit leave A/THR at Vfloor"?
(Also it is A.floor, not V.floor - is an angle of attack, not a speed. It is possible to get A.floor protection activate at a speed well above Vls, by pulling back hard enough to increase angle of attack to above the A.floor value)

2) Yes. FAC knows current angle of attack from the probes. FAC also calculates the value of A.floor from the config of the aircraft. FAC makes a simple comparison of the two, and any time AoA > A.floor, activates the protection by signalling the Autothrust to give TOGA.

3) It is confusing and I am not entirely sure. My best guess is option (1). What remains unknown to me is whether the FAC tells the ELAC the value of V.a.prot or whether the ELAC calculates it itself.

Ok...confused.

Are you a real airline pilot? ;)
Well, I really appreciate your help! Thanks a lot! Here are my doubts:

How can you get alpha floor above VLS?
VLS is the lowest speed you can select. Vprot is the speed where the maximum AoA at which Alpha protection becomes active (the plane pitches down and maintains Vprot with ELAC).

You can only reach Vprot if your thrust levers are at IDLE.

At Vmax, your plane is stalling so your speed is below VLS.
I haven't seen any stall with TOGA thrust... (so why is Vprot and Vmax BELOW VLS????)

You say that Aloha floor is a special AoA where you basically start stalling (between Vprot and Vmax - VSW). I agree with you.
But then you say that you can have Afloor above VLS.
If you are stalling, you don't have enough lift ---> Your speed is low.
So at a special AoA, you get TOGA from A/THR.

Do you have a video where you hit Afloor and you get TOGA LCK above VLS???

My question: Can we stop A/THR to give us TOGA when we are at Alpha Floor? Or can we only stop A/THR when we have left the critical AoA (A.floor)?

Thanks a lot!

haha yes I am... well at least i try to be one. What is your interest in these questions? they are very detailed!

Did a youtube search and came up with this. It is only a microsoft flight sim vid (and is not mine) but illustrates the point. Thrust does not need to be at idle to activate A.floor. I have done it myself in full flight sims a few times (normally associated with a gpws manoevre which requires full backstick and manually selecting toga, which is quickly replaced by A.floor (also toga)) but obviously never in the real aircraft.

The actual stall speed is always below V.a.max. At A.floor you still have a reasonable margin above the stalling AoA.

Your question - answer is the second one. You cannot stop it giving you TOGA and can only get out of TOGA when AoA is above A.floor. That is if you have protections... if you have some failures that put you in alternate law without protections then you will not see A.floor at all.

Thanks a lot,

Yes....

1) Basically, Alpha prot is also an AoA. The plane just shows where your Alpha prot/floor/max AoA is if you keep this attitude. Do you agree? But he/she pulled the stick, the attitude changed ---> A new Alpha protection AoA. Right?

2) Something very intresting in your video:
A/THR doesn't go below VLS. So it remains ON.
So what happens? Ok...here he reaches Alpha Floor AoA.
--> As A/P is OFF, the default mode is SPEED. When you pull the stick, as you are still above VLS, A/THR tries to maintain that speed. But as you pull the stick, you reach Vprot (A/THR still ON). So I had said that as A/THR is OFF, Vprot managed by ELAC (completely wrong for the first part).

---> As, A/THR is ON, can Vprot be managed by A/THR? Or is it ALWAYS ELAC?
Ok, so you can NOT disconnect A/THR at AoA Alpha floor.

Question 2:

---> In that case, Afloor was over VLS.
We can also notice that 2 things come on the FMA:
- A.FLOOR (I think that at that moment you can NOT disconnect A/THR)
- TOGA LCK (You can disconnect TOGA).
But I imagine that Alpha max is BELOW VLS.
But I can not see the VLS bar. (maybe it's hidden in the red part!)
What do you think?

Question 3:
What are the ways to leave A/THR.? In his case, we didn't even see what happens to the thrust levers! We just see that he goes back to SPEED mode!!!!
Do the levers move to TOGA? How does he come back to A/THR range??
Well, he disconnects A/THR ~ 140kts. So it's enough (and I think that his levers are already at CLB - A/THR range)

Thanks a lot,
AF330

1. Almost. V.a.prot and V.a.max take account of current load factor (LF).

To correct your quote "But he/she pulled the stick, the LOAD FACTOR changed ---> V.a.prot moved up the scale to a speed that would now (with the big LF) result in.... Alpha protection AoA"

I am not aware of athr disengaging below Vls... do you have a reference for that? What does disengage is the autopilot, at alpha.prot +1°

The high AoA protection works by reducing pitch attitude only. This is ELAC control, Athr has nothing to do with it. However Athr, when engaged will always try to maintain target speed. Min target speed is Vls, so when engaged it is always trying to maintain a higher speed than v.a.prot anyway.

Also, the athr is limited to how far advanced the levers are. so if you have them near idle, with athr on, maybe it cannot even maintain Vls. Normally they are in CLB detent, giving the athr authority to command anything from idle to climb thrust.

2. Because Vls doesnt change with load factor, it stays constant, while V.a.prot and V.a.max shoot up the speed scale. For a brief moment, V.a.max is above Vls.

3.The levers are not back driven, so they stay where the pilot put them.

The whole sequence breaks down...

Athr on, speed mode, target 165kt selected.
Vls 135kt, constant.
Pulls stick back, big LF generated.
Airspeed decreases and V.a.max shoots up. Athr still targetting 165.
Airspeed and V.a.max meet at 158kt, and the ELAC forces nose down to keep AoA at V.a.max
A.floor activates simultaneously. Thrust goes TOGA.
Pilot relaxes the stick, allowing LF to decrease, V.a.prot/max go back down.
No longer in A.floor, thrust still in TOGA, FMA changes to TOGA LK
Pilot pushes instinctive disconnect, Athr disengages. Thrust now manually controlled.
Pilot pushes the Athr button to re engage. It engages, in THR LVR mode which indicates thr levers are below the CLB detent. Target speed now 165kt.
Pilot puts levers in CLB detent, FMA changes to SPEED

Thanks a lot,

1) What is load factor?

2) But at AoA alpha protection, ELAC maintains Vprot. But you say that A/THR is still trying to manage the selected speed. That is impossible. One is trying to manage Vprot, the other one is trying to maintain 165kts!!!!! Does FAC's send a signal to A/THR to stop sending orders to FADEC/FMGS at Vprot?

3) How do A/THR signals work? FMGS sends the next speed/altitude (constraint). A/THR knows the plane's IAS. A/THR calculates the fuel required and sends it to FADEC (ECU). It then sends a signal to FMGS to tell him the pitch required if in CLB/DES mode.
What do you think?

I also have some questions about Airbus laws, would you mind If I ask them?

I am just waiting for your answer and normally we will be good for AoA protections! ;)

1. Load Factor is the vertical g force the aircraft experiences. (Lift/Weight).

2. ELAC controls pitch. Athr controls thrust. The ELAC will only need to pitch down to avoid stall if the autothrust is insufficient to accelerate the aircraft. The autothrusts target is higher than V.a.prot or V.a.max... they are both moving to accelerate the aircraft.

It would only be a problem if their targets were in opposite directions.

Practically, the only was to activate this protection is to 1. disengage autothrust and use low thrust, or a steep climb to reduce speed. 2. Keep autothrust on, but retard the thrust levers far enough back that you restrict the autothrusts authority so much that the aircraft reduces speed even though autothrust is giving its max thrust. 3. Pull back on the stick so hard that the V.a.prot/max go above your airspeed.

3. Quoting FCOM-DSC-22-30-90-GENERAL
"The autothrust (A/THR) is a function of the FMGS, it includes two independent A/THR commands, one per FMGC. Each one is able to control the thrust of both engines simultaneously through two Engine Interface Units and two Electronic Engine Controls (IAE engines) or two Engine Control Units (CFM engines). Only one FMGC controls the active A/THR, it is called the master FMGC."

So the Athr is a part of the FMGS. FMGS knows the target speed (Managed or selected), and current speed. The ATHR part then works out how much thrust it wants, and sends this to the EIUs, which in turn tell the FADECs, which work out how much fuel to put in the nozzles.

Separately, the FMGS calculates the pitch required and sends this to the FD

Another quote, this time about how the FD pitch mode and Athr mode relate.
FCOM-DSC-22-30-10-INTERACTION BETWEEN AP/FD AND ATHR MODES.
"The AP and FD pitch modes can control a target SPD/MACH or a vertical trajectory, and the A/THR mode can control a fixed thrust or a target SPD/MACH. However, the AP/FD and the A/THR cannot both control a target SPD/MACH simultaneously. Therefore the AP/FD pitch modes and A/THR mode are coordinated as follows:‐If an AP/FD pitch mode controls a vertical trajectory, the A/THR mode controls the target SPD/MACH.‐If an AP/FD pitch mode controls a target SPD or MACH, the A/THR mode controls the thrust.‐If no AP/FD pitch mode is engaged, the A/THR mode reverts to controlling the SPD/MACH mode. In other words, the selection of an AP/FD pitch mode determines which mode the A/THR controls.


Go ahead Ill see if i can help.

What makes you so interested in these things?

Thanks for your answer.

I just love Airbus! ;)

1) Ok, but I still don't get it.

If ELAC is controling pitch and A/THR is controlling thrust, do you mean that if A/THR is ON and if we reach Vprot, ELAC will just pitch down at a certain programmed value and A/THR will keep trying to maintain the selected speed but if A/THR is OFF, when we reach Vprot, ELAC will pitch down and manage itself the Vprot? So:
A/THR ON = ELAC pitches down at X° (programmed) - target speed managed by A/THR.
A/THR OFF = ELAC pitches down and maintains Vprot.
Am I right??

2) What is EIU's use?

3) Ok, A/THR will send X fuel amount to FADEC.
A/THR is part of the FMGS. FMGS knows the target speed.

Ok so you are saying this:

If A/THR is in SPEED/MACH mode, AP/FD control pitch.
I really don't understand then...what do you mean by vertical trajectory??
Do you mean to say what I have written before?

Well, for me, If A/THR is in SPD mode, pitch is then controlled by FMGS.
If A/THR is in CLB/DES mode, pitch and thrust are controlled by A/THR. What is FMGS doing?? He always controls the trajectory...A/THR never controls HDG/CRS.
How can AP/FD control a target SPD? Or do you mean, FD/AP controls pitch?
Don't get your last F-COM quote.
Please explain,

EDIT:

When AP/FD manages vertical trajectory: Does that mean that AP/FD are managing pitch? Or is it simply the route?

When A/THR manages a target SPD/MACH: Does that mean that A/THR is in CLB/DES mode and is pitching up/down to maintain target speed? So - to make it shorter - A/THR controling pitch?

When A/THR is controlling thrust: Well, that's speed mode, isn't it?

When AP/FD is controlling a target SPD/MACH: ???????? A/THR will always control speed (by pitch or by thrust). So what is this???

Thanks a lot

I really want to finish Afloor and stuff before talking about the laws..

Thanks

1. Think of it like this:

ELAC makes sure that the aircraft will not go BELOW V.a.prot/max. It is a minimum speed, not really a target speed as such. It will pitch down just enough to maintain the minimum airspeed. No more, no less. It is not a fixed value, and depends on lots of factors.

Say you are climbing really steeply, and the autothrust is already at Climb power, but you are still decelerating. When you reach V.a.prot/max the ELAC will not allow you to climb that steeply, so will lower the nose so you don't go below and stall.

2. EIU (Engine Interface Unit) is the bit that interfaces between the FMGS and the FADEC. Not sure exactly what that means... I have a picture of the architecture but can't figure out how to post it on here. If you can help, I will post it!

3. By vertical trajectory it means a certain climb rate or flight path angle.

Just briefly (I have to go to work, will be back on Jan 1st)

Set yourself up in the simulator, normal flight, Athr On, FL300. Select speed.
Select FL100, pull for open descent. You will see Athr commands THR IDLE. Select a high speed, watch as the pitch increases, descent rate increases, then reduces as the speed is reached. Then decrease selected speed (say by 20kt) and watch as it increases pitch, reduces descent rate, to decelerate, then steepens up the pitch once the speed is reached.

Now turn off autothrust, set a low thrust value (say 700kg.hr per engine). Do the same. It will pitch to maintain the speed. Thrust is fixed, so it will give whatever pitch is required to maintain the speed.

Now re engage autothrust, and select vertical speed -1000fpm. Again increase and decrease the selected airspeed, and watch how the autothrust compensates to maintain it this time, not the pitch. This is because the FD is controlling the VERTICAL TRAJECTORY.

When you are done, set up a climb and do the same exercises (using climb thrust if Athr is not on) and see how it works there - pretty much the same.

That should give you a good understanding.

Sorry I won't be around for next couple of days!

Thanks,

Well, will come to A/THR when you will be back! ;)

So you said: " ELAC makes sure that the aircraft will not go BELOW V.a.prot/max. It is a minimum speed, not really a target speed as such. It will pitch down just enough to maintain the minimum airspeed. No more, no less. It is not a fixed value, and depends on lots of factors.

Say you are climbing really steeply, and the autothrust is already at Climb power, but you are still decelerating. When you reach V.a.prot/max the ELAC will not allow you to climb that steeply, so will lower the nose so you don't go below and stall."

I agree with you - but - I am 99,9% sure that airbus will maintain Vprot after piching down (Flight Detent said it in his previous posts).
---> So I agree with you if A/THR is ON. ELAC will pitch down the aircraft. A/THR (over VLS!), will still try to maintain the target speed. ELAC has been programmed to pitch down at X° if A/THR is ON.
But what if A/THR OFF? We had said that ELAC will MAINTAIN Vprot by pitching down. I don't think it's more complicated. What do you think? Hope it's right...

Kind regards,
A.Roy

it really doesnt matter iv athr is o or off. The protection works the same way i.e. if speed decelerating to v.a.prot, elac orders pitch down so as yo avoid speed dropping any lower.

As for elac maintaining v.a.prot? Once the plane is capable of flying faster, it will do so, and the high aoa protection is no longer active.

You say "airbus will maintain Vprot after piching down". Are you saying that the elac will maintain v.a.prot even after the plane accelerates, by pitching up??

Hmmm...good point.

Are you 100% sure that ELAC simply pitches down the aircraft? So what happens if ELAC itself hits VMO/MMO?? That will happen if you don't do anything.
If A/THR is ON, then it's fine.
MMO/VMO protection will come if you don't do anything...

So yes, i thought that ELAC could pitch up to maintain Vprot but as the speed is already low, so if it keeps pitching down, it will maintain Vprot. No need to pitch up.

Are you sure?

"Are you 100% sure that ELAC simply pitches down the aircraft?" What else do you think it could do?

When high speed protections activate, the elac commands pitch up to prevent excessive overspeed.

The protections are just maximum/minimums that the elac will not allow the plane to exceed, regardless of thrust setting, stick input etc. Once the speed is within the extremes again, the protections are not active and the plane returns to normal law.

Once again I learn something new.

Quote FCOM-27-20-10-20 HIGH AOA PROTECTION

"To deactivate the angle of attack protection, the pilot must push the sidestick:‐Greater than 8 ° forward, or,‐Greater than 0.5 °for at least 0.5 s when α < α MAX. In addition, below 200 ft, the angle of attack protection is also deactivated, when:‐Sidestick deflection is less than half nose-up, and‐Actual α is less than α prot – 2 °.
Note: 1.At takeoff α prot is equal to α MAX for 5 s.
Note 2.αfloor is activated through the A/THR system, when:‐α is greater than αfloor (9.5 ° in configuration 0; 15 ° in configuration 1, 2; 14 ° in configuration 3; 13 ° in configuration FULL) or‐Sidestick deflection is greater than 14 ° nose up, with either the pitch attitude or the angle-of-attack protection active.
The αfloor function is available from lift-off to 100 ft RA before landing."