A320 questions

[JeanV]

Could someone answer to these questions about A320 ? Il would greatly help me.

1/ How works fcu speed/mach, heading/track, and altitude knobs : Have they three positions : Selected (pulled) Managed (pushed) and the inactive position(disengage selected or managed mode). Or are they only used to engage a selected or managed mode. In this case, how disengage them ?

2/ What exactly is Vls ? when is it represents 1.13 Vs or 1.23 Vs ? is it depends on load factor like Vs, Alpha protection and alpha max spd ?

3/ About the Engine rating limit control : FLEX power can be used for takeoff if a FLX temperature has been entered via the MCDU. When Flex power becomes inactive ? Is it replaced by maximum continuous thrust ?

4/ Finally, what is the conditions needed for a LOC and GS capture ?

All explanations would be appreciated !

[Boxer]

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1/ "How works fcu speed/mach, heading/track, and altitude knobs : Have they three positions : Selected (pulled) Managed (pushed) and the inactive position(disengage selected or managed mode). Or are they only used to engage a selected or managed mode. In this case, how disengage them ?"

ANS... It has a neutral position and you engage/activate eitheir mode by pulling or pushing. After the action it will return to neutral. To disengage a mode just activate a different one.. i.e. if you have selected a speed then just PUSH it and it will reverte to Managed and vice versa

2/ What exactly is Vls ? when is it represents 1.13 Vs or 1.23 Vs ? is it depends on load factor like Vs, Alpha protection and alpha max spd ?
:)
ANS... VLS is the minimum selectable clean speed. 1.13 (V2) as far as I remember is on departure where as 1.23 (Vapp) on approach. They are multiples of Vs1g. Alfa prot is a high angle of attach protection..... too long to explain all the protections. As for Alfa Max...well this is the min speed/angle of attack the A/C will fly at depending on config... it really onlys gives you enough speed so as to give you enough air flow to give a roll rate. Level flight may not be achivable.
:)
3/ About the Engine rating limit control : FLEX power can be used for takeoff if a FLX temperature has been entered via the MCDU. When Flex power becomes inactive ? Is it replaced by maximum continuous thrust ?
:)
ANS..Engine rating limit... basically it is like a govener... it wont let you over boost the engine... Flex..no you firstly get an ECAM warning to tell you to select toga but it should give you climb power... a bit vague at this hour I'm afraid
:) :)

[atomic]

Hi!

1. I know what Boxer means by saying 'neutral' position, but looking at your question, I have to deny this. The knob itself always stays where it is, it never stays in or our. If you push, you're in manged mode, if you pull, it's selected mode.
Pull on the knob and you see the current speed displayed in the FCU window and the airspeed indicator shows you a blue little arrow/ triangle. Push the button and the numbers in the FCU window disappear, a white dot shows up and the symbol on the PFD turns magents and moves to the managed speed calculated for the phase of flight: managed mode. If you just turn the speed knob without pushing or pulling, it shows the current speed. You can now go, select a speed and when you're ready, you pull and this becomes your selected speed. If you don't pull, this number will disappear after maybe 30 secs and the dashes reappear since you're still in the managed mode. You can pre-select some speeds in the MCDU during preflight. If you want a managed climb speed, as calculated by the FMGC per cost index etc but you want a constant M.80 cruise speed, you just enter this into the PERF page for cruise (anytime before the mode becomes active) and when you reach cruise altitude, the FCU window shows .80 (mach) AND the white dot, indicating that even though you told it what speed to fly, it is still in the managed mode. It manages speed now with your preset speed instead of its own calculated. But: either managed mode or selected, nothing in between, no situation not being in either mode.

2. Vls is the minimum maneuvering speed for the current configuration. You will find two different Vls speeds on the plane. One is on the PERF APPR page in the MCDU. This is a static number and is calculated as Vref for landing using Flaps FULL (unless you tell the box to use Config 3).This provides 1.23 Vs protection . Then there is Vls as it shows up on the PFD airspeed tape. This constantly varies according to the current configuration and flight condition.
It is the minimum speed the airplane will fly with the autoflight system on. If it's e.g. 140 kts and you select a speed of 120 kts, the autoflight system will slow to 140 kts and stay there. In itself, Vls has nothing to do with Alpha Prot or Alpha max.

3. First, when you think max continous, think engine failure. You don't use it for normal flight. The detent is called FLEX/MCT, which means that during normal ops, it provides FLEX power as long as there is a FLEX temp entered on the PERF page and it is higher than the current TAT. If one engine fails, the airplane thinks differently now and the same setting now provides MCT as soon as you reach the acceleration altitude during climb. If there is no FLEX temp entered or if the FLEX temp is equal to or lower than the current TAT, the ECAM will tell you use TOGA if you set the thottles to the FLEX/MCT detent during take-off.

4. I'm not really sure what you're asking here. The GS and LOC act like any other airplanes receivers. They do false captures etc. like on any other airplane, no difference there, let me know if there is something specific , related to the FMGC etc. that you're looking for.

[JeanV]

Boxer/ atomic, thanks for your replies. :)

1/ Concerning FCU, your explanations have really enlightened me. Only two positions : managed or selected. It means that as soon as an autopilot is active (AP switches on FCU), all guidance mode becomes active, (Speed, Heading/Track,, Alt, Vertical spd/flight path angle) in either managed or selected mode. Therefore, I can't engage only speed or altitude, without having other modes active ?

2/ For Vls = 1.23 Vs as a Vref for full flap landing, ok.
Atomic, you said " Vls as it shows up on the PFD airspeed tape. This constantly varies according to
the current configuration and flight condition. "
Does " flight condition " used to compute this Vls include the load factor ?
I mean : will Vls value change between a 1G flight and a 1.3G flight.

3/ No problems. http://www.pprune.org/ubb/NonCGI/cool.gif

4/ I saw that with APPR switch armed above 8200' AGL, glide slope capture was disengaged because of the loss of Radio Alt signals above this altitude. I would like to know if others constraints exists concerning LOC and GS capture, especially considering relative runway / airplane positions.

[Boxer]

With regard to Vls.... I think (correct me if I'm wrong Aomic) Atomic means config and bank angle, as for load factor in wings level no change but while in the turn then your Vls will incrase. The side stick is demanding a constant load factor of 1G and only if Abruptly used will you increase your load factor.
As for mode engagement... I'm not quite sure of your question, but I'll try, you can select or manage speed without ever having activated the vertical (alt) mode. You can do this with AP engaged or disconnected, same is true for ALT modes.
With regard to Appr mode, I think I now get your question...... loc has no limit (with in reason 25nm or so) for engagement whereas GS is predicated on which RA system is fitted. Collins as far as I know use 5000' as a limit for GS capture.
Atomic.. correct me if I'm wrong but if during take off and V1 failure occurs there is no change in power setting even at acc alt. It is only activated (mct) after you move thrust levers out of the flex gate and back into to them. :)

[This message has been edited by Boxer (edited 01 October 2000).]

[atomic]

You're absolutely correct, Boxer, and i forgot about the MCT thing: Yes, you have to briefly move the throttles out of the detent and then back into to get MCT after engine failure in FLEX.
The basic autopilot engagement mode is Speed mode with Vertical Speed as the vertical mode, and HDG. When you handfly around the sky and turn on the autopilot without flight directors on, it will engage in this basic mode. If a flight director was already on when you turn on the autopilot, it will engage in the current active modes.
For the GS/LOC thing: Our manual says not to arm the Approach above 8000' AGL (used to be 8200') due to, as Boxer said, lack of Radio Altimeter signal. If you still arm it, the system will revert to HDG and V/S upon Glide Slope intercept. Also, you have to have an ILS Approach selected from the database. If you select a non-ILS approach and push the ILS button, you get a flashing 'V/DEV' on the PFD. You always do something in the vertical direction (at least ALT or V/S up or down) and something in the horizontal plane (HDG ) So as a basic mode, the autopilot always engages in one lateral mode, which must be a HDG if the managed mode (NAV) is not active, and it engages in one vertical mode, and that must be either being level at a constant altitude (ALT) or going up or down with a certain V/S . The autothrottles engage either in SPEED when you fly V/S since this is a range of speeds so the autothrottles can adjust thrust to maintain this rate. Then there are the 'fixed' modes of CLB, MCT, TOGA which are fixed thrust settings. I think the basic idea is that when you turn the autoflight system on, it just keeps on flying what the airplane was doing at the time of engagement.
That's why it goes into Speed, V/S, HDG to just keep on doing what the airplane is doing this very moment. If a Flight director is on and you follow a managed guidance, then the autopilot engages in this current managed mode since it now knows what the airplane will be doing since it already knows where the plane will go, vertically and laterally.
For the sidestick: Pitch is a function of load factor demand. The system trims for 1 g level flight when the stick is in neutral. Whenever you move the stick in the pitch axis, you demand a loadfactor , up to the maximum allowed when you go to full deflection. If you yank the stick back, you immediately demand a high load factor and the bus will probably do something close to the limits for the current configuration (+2.5 to - 1.0 g for clean or slats extended and +2.0 to 0g for flaps extended).
Yes, configuration and bank angle for Vls. I've seen this, taking off with a heavy airplane with a turn toward the airfield after take off. When you accelerate to 'S' speed the Vls is not much of a factor ,but 'S' is very close to Vmax with the heavy weight, so you want to initiate the retraction right when you get to 'S' speed. If you are in a , let's say 20 degree or more ,bank, you might see Vls shoot right up through your current speed and the FOQA Swat Team (Flight Ops Quality Assurance) will storm your house the same night interrogating you as to why this happened.
I then usually fly at a slower speed until I can fly straight ahead and then accelerate to 'S' Speed and retract the Flaps/Slats.
G/S and LOC in the US are described in the AIM with the certified service areas. I think your standard LOC is good for intercept around 18 NM out. The question that came up: At ORD, Approach clears you to intercept the loc for let's say 14R about 45 NM out. Even though you get a good ID, you wonder: If there is a deviation out here tracking this LOC, am I then responsible for accuracy outside those 18NM?? No, some localiser facilities are certified to navigate at far greater distances. So it all depends.

[JeanV]

Boxer and Atomic, thanks again !
I understood and appreciated your explanations. I just would like to add something about sidestick : As you said,
the Stick, on pitch axis, demands a load factor (limited to +2.5/-1 or +2.0/0), and neutral position corresponds to 1G flight.
However, i've noticed a little contradiction: In normal law Roll mode, up to 33° bank angle, roll attitude is held if
the sidestick is in neutral position. Therefore, during a turn, neutral position corresponds to the load factor
created by the bank angle (n = 1 / cos(bank angle)) and not 1G as indicated on the manual. http://www.pprune.org/ubb/NonCGI/confused.gif
If Pitch mode maintained 1G in a turn, a pitch-down tendency would exist, in order to compensate load factor increase.

[atomic]

You are absolutely correct and that's why our manual says that it maintains 1 g with the stick neutral in level flight.

[Royan]

Very much enjoyable discussion .

[Three-Twenty]

My ha'pennorth..

atomic, as for the heavy aeroplane/slat retraction thing, good thinking with flying a slower speed until level for slat retracation, but do you use the 'flaps auto retract' when Vmax is reached?

In my experience this moves Vmax right out of the way and allows for F zero selection at S speed in the normal way, so you can create a bit more of a margin between your speed and VLS.

Also, haven't felt the need to try it myself, but with THR CLB and Managed SPD, can't you just leave it alone? It 'should' pitch up to prevent overspeed at VMAX + something or other. And would you get a ECAM warning before the pitch-up or after? Must check the books.

FWIW my company has no problem with arming APPR at greater than 8000'agl, in fact, it is often (though with a few drawbacks) used to slow to green dot for the hold, particularly on the A321. Or are you referring to arming it with a view to capturing ther GS/LOC at 8000'+/long way out?
I've found that on some very long straight in apps it sort of rocks from side-to-side with LOC* at very long ranges. Best thing to do, either go HDG or just fly using that little black handrest on the Right hand side (or left!).

TTFN

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So what's my left hand for?

[Boxer]

Just to interject a little if I may Three twenty.. I think atomic was refering to wings level rather than LEVEL FLIGHT. I have no doubt atomic will correct me if I assume too much. As for the auto retract system.... well there are a few different opinions on this, firstly you are flying the flaps to their limit and there fore stressing them unnessarily. The other being "Alfa Lock" in other words if they are not supposed to be retracted (too slow) then they will not come in.
Vmax and VFE are two totally things and by bringing in the trailing edge you have not changed any limits you are just accelerating to the next limit and is only relevant when S speed is greater than 215kts. As some others may agree (or not) it is never good to fly an A/c at its limits.
As far as I remember you can overspeed the flaps in THR clb and managed speed and yes you get an overspeed warning AT the limit.
Arming the approach DOES not slow the A/C to GD speed!! Activating the approach does!!!!
As to why the A/C rocks from side to side on the approach you will probably notice you have traffic ahead and therefore he/she is also flying the ILS and the signal is reflected around the preceeding A/C.
I hope you dont take this as being too inflamatory......
Happy Hunting.... :) :)

[This message has been edited by Boxer (edited 09 October 2000).]

[Three-Twenty]

fatigue takes its' toll!

I meant wings level.

And I misread arming APPR for activating appr phase. D'oh!

Interesting about the ILS rocking thing.

Flaps limits...shall have to have a think. (Company trng capts think it OK tho')

..or wasn't I paying attention then either?

Thanks mate! :)

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So what's my left hand for?

[atomic]

...for all the goodies on the tray table.
Flaps: Our performance section in the manual lists a 'S' speed of 214 kts at max weight. 'S' speed is defined in my manual as the minimum slat retraction speed. Since we are in Config 1 + F , no matter if we take off in Config 1, 2 or 3 , we then have to wait until we reach 214 kts before we can initiate the retraction to Config 0. But we know that the flaps start to autoretract at 210 kts. I ws just about to write a note to our fleet, when I ckecked the limitations section in our manual. There is a note next to the flap limit speeds that says: Do not exceed the limit for any flap setting (except as directed by a procedure or during flap retraction) to prevent excessive wear on the flap assembly. That says it all. Even though getting an auto retract on other aircraft means that you must have gotten too fast for the given config and the plane is trying to save itself from you, here it is OK, there even is no way around this. I was told (engineers, please confirm or deny) that the loads on flaps are not really that severe at a setting like 1+F , this only gets to be a big factor when the flaps are out much further , like in Config 3 or FULL.

[atomic]

Two more comments:

1. Alpha Lock: It only prevents retraction of the slats , not the flaps when you're in the AOA protection range.

2. My experience is that not the flap movement changes the Vmax indication on the PFD but the handle position. Whenever you move the flap handle, the Vmax indication immediately jumps to the new value for the selected setting. Other than the Vls which reflects the current situatiion at any given time. You can see that when you use various speed brake positions: Vls dynamically adjusts.

[Boxer]

Atomic.... Vmax.... sorry but I lost you on that, are we talking about VFE or V ALFA MAX?
Just a little slow on the pick up tonight...on the S speed thing.... you said that slat retraction is done at 210 knots,as a max yes but not a constant, I would have thought that S speeds varies relative to weight which we assume the AC to be, as for green dot and VLS well while flat/slats are extended I think Let me stress the think bit that these indications are calculated by the FAC from our inputted weight. It is at Slat 0 that there can be a change in the computed speeds as the FAC recalculates the weight of the AC via C of G , Alfa, fuel flow etc.... it does this while the AC is 250 kts or below and below 13500 or 14500 (cant quite recall whic alt) How does that sound Atomic or did I jump the gun?

[This message has been edited by Boxer (edited 11 October 2000).]

[atomic]

Boxer! By saying Vmax I meant the maximum speed for the current configuration, be it Vfe, Vle. I am talking about the bottom of the red and black barberpole, wherever it is at the time. The comment about Alpha lock comes from your comment on it in a previous post, regarding the auto retract system. You mentioned the stress on the flap system and then talked about 'Alfa lock' as another consideration. But Alpha lock only relates to inhibition of slat retraction in a low speed/ high AOA situation and that confused me a bit , I guess,since we were talking about the auto retract in relation to high speeds/ exceeding flap limit speeds.And this is a slat function only, not the flaps. S speed is constant for a given weight. If you take off at max gross on a A320, the tables list S speed as 214 kts for that weight. For 150K pounds it lists at 200 kts etc. Sure, you will burn a few hundred pounds by the time you get there, but unless your weight drops to less than 166K pounds , your S speed will be above 210 kts (remember, this is a performance book exercise here) , and 210 kts is listed as the speed at which the flaps start to auto retract ,not the slats since they stay out until you move the handle to Config 0 . For our exercise: we weigh 167k pounds right this moment, S speed is 214 kts, we reach 210 kts, the FLAPS start to auto-retract, the SLATS stay where they are. We reach 214 kts, S speed, the MINIMUM speed to initiate SLAT retraction.
We move the handle to position 0 and the SLATS now retract, while the FLAPS are either up already or still retract, don't know if the auto-retract system retracts them quicker than the normal process with the handle.

[Boxer]

OK got ya this time... Vmax being VFE... no argument on the Alfa lock, I referred to it in relation to auto flap retraction V too early on the flaps...one extreme to the other and only meant to referr to SLATS , aploigies if misleading, on the matter of 210 v 214... I wasnt quite sure in your text if you had meant the speed was fixed... as for the perf A lesson, always willing to learn new things!

Happy Hunting.....

[This message has been edited by Boxer (edited 11 October 2000).]