Heavy A321
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Heavy A321
There was rather hot day and we perform TO on A321 with mass of 82tons. after an accel hight we engage AP and retract flaps in pos 1. The S speed was 211 and upon reach it there was autoflap retraction. So the next step Flaps 0 and... the Vls of clean configuration arose up to 220. Due to very slow a/c acceleration we were forced to disconnect the AP and handle the a/c so as not to be below Vls clean. In addition there was turbulence.
May be you have some thoughts how avoid AP disconnection!
Any comments appreciated.
May be you have some thoughts how avoid AP disconnection!
Any comments appreciated.
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The FCTM has a reference to the problem you encountered, it is under supplementary information, adverse weather, turbulence.
It states that during take off in high turbulence the flight crew must wait for the target speed +20 kt (limited to Vfe -5 kt) before retracting slats/flaps.
It is quite normal that S speed on take off will be almost equal to Vls once the slats are retracted, hence in turbulence you are likely to dip below Vls, that is why they recommend to keep that extra speed buffer.
Of course you will get close to your Vfe when on a heavy take off.
We only fly the A320, so S speed for us is usually much less than what you saw on that take off, but we do the same thing on the A330/A340 on heavy take off weights in turbulence.
Safe flying!
It states that during take off in high turbulence the flight crew must wait for the target speed +20 kt (limited to Vfe -5 kt) before retracting slats/flaps.
It is quite normal that S speed on take off will be almost equal to Vls once the slats are retracted, hence in turbulence you are likely to dip below Vls, that is why they recommend to keep that extra speed buffer.
Of course you will get close to your Vfe when on a heavy take off.
We only fly the A320, so S speed for us is usually much less than what you saw on that take off, but we do the same thing on the A330/A340 on heavy take off weights in turbulence.
Safe flying!
Pensador- You answered your own question. You were not forced to disconnect th A/P you used the appropriate level of automation as prescribed by Airbus. That is, disconnect the A/P when it is not coping with the conditions and it is putting you in a situation that you don't want to be in. Under the conditions you describe, manually control the aircraft until you are accelerating and you are comfortable with your margin over Vls. Then continue to enjoy the art of flying or let the A/P do it.
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Toby, consider that even in the event of an EFATO, you push to level off and accelerate in level flight. They had 2 engines, thus they would be both higher and acceleration would be correspondingly quicker. I expect that there would be more than enough margin climb performance.
Is it a requirement to disconnect if the aircraft does not maintain VLS? I often see pilots 'adding a few knots onto Vapp' because they are worried about reducing below Vls - but Vls is the lowest selectable speed, not the stall speed. The aircraft might lag a bit when heavy but give it a chance...a few knots below Vls for a few seconds while it adjusts the pitch attitude isn't going to kill you.
However, as ALK said, the key is/was (with 20/20 hindsight and knowledge of the FCOM), wait until well above S speed before retracting in the case of turbulence and/or very heavy weights.
Is it a requirement to disconnect if the aircraft does not maintain VLS? I often see pilots 'adding a few knots onto Vapp' because they are worried about reducing below Vls - but Vls is the lowest selectable speed, not the stall speed. The aircraft might lag a bit when heavy but give it a chance...a few knots below Vls for a few seconds while it adjusts the pitch attitude isn't going to kill you.
However, as ALK said, the key is/was (with 20/20 hindsight and knowledge of the FCOM), wait until well above S speed before retracting in the case of turbulence and/or very heavy weights.
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Gary Lager, you know, if we wait till speed will be well above S speed the OVERSPEED warning may be trigged. But about the short flight slightly below Vls I am rather positive. Thanks a lot 
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ALK A343б I didn't find any recommendations in our suplementary adverse weather.
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Gary Lager.I agree about VFE but the overspeed warning doesn't depend on th flaps leather position. The slats retracts so slowly!!! If actual speed is grater than 230kt and a system detects the actual slats/flaps position more than 0, be sure about he overspeed warning coming on.
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Pensador, It is in our FCTM (flight crew training manual) not the FCOM.
But maybe we could be having different FCTMs as Airbus has customized ours.
As far as Vfe displayed on the PFD is concerned Gary Lager is right, it depends on the Flap Lever position.
The actual overspeed warning, i.e. the CRC, is based on the actual slat position, so as soon as the surfaces retract the warning threshold increases above 230 kts. So if you follow the Airbus recommendation and retract the slats before Vfe - 5kts, you should not get an overspeed warning unless there is a slats fault or lock.
Also think about this, when the flaps autoretract at 210 kts you are only 5 kts below your Conf. 1+F Vfe of 215 kts. How often did you get an overspeed warning in that situation?
But maybe we could be having different FCTMs as Airbus has customized ours.
As far as Vfe displayed on the PFD is concerned Gary Lager is right, it depends on the Flap Lever position.
The actual overspeed warning, i.e. the CRC, is based on the actual slat position, so as soon as the surfaces retract the warning threshold increases above 230 kts. So if you follow the Airbus recommendation and retract the slats before Vfe - 5kts, you should not get an overspeed warning unless there is a slats fault or lock.
Also think about this, when the flaps autoretract at 210 kts you are only 5 kts below your Conf. 1+F Vfe of 215 kts. How often did you get an overspeed warning in that situation?
Last edited by ALK A343; 14th May 2009 at 03:22.
This will happen, do you need to worry about it... no.
FCOM states Flap retraction at s speed AND accelerating.
S speed is 1.29 Vs, while Vls in clean config is 1.28 VS so on a normal day there shouldn't be any overlap.
Only my opinion but consider a Config 1 + F Take-off. At you ACC ALT you are well below S speed but the aircraft will accelerate towards S speed. This is similar, but you are accelerating to and past you manouvring speed of Green Dot instead.
At S speed when you select Flap 0 it may be just below VLS, though it is about 56kts above the stall speed. Just relax. you will find its one of those French Autoflight laws regarding negative G's. It has fully authority but usually wont command the full and abrupt pitch down until you get to about VLS -5 or so.
If it doesn't fix itself up, yeah sure follow the golden rules, disconnect, and manually pitch down as you did... good call. In my experience, it would "eventually" pitch down, just beware the "Garfield" (Alpha Prot) during the turbulent and hot conditions in this scenario because this may make things a little bit trickier.
FCOM states Flap retraction at s speed AND accelerating.
S speed is 1.29 Vs, while Vls in clean config is 1.28 VS so on a normal day there shouldn't be any overlap.
Only my opinion but consider a Config 1 + F Take-off. At you ACC ALT you are well below S speed but the aircraft will accelerate towards S speed. This is similar, but you are accelerating to and past you manouvring speed of Green Dot instead.
At S speed when you select Flap 0 it may be just below VLS, though it is about 56kts above the stall speed. Just relax. you will find its one of those French Autoflight laws regarding negative G's. It has fully authority but usually wont command the full and abrupt pitch down until you get to about VLS -5 or so.
If it doesn't fix itself up, yeah sure follow the golden rules, disconnect, and manually pitch down as you did... good call. In my experience, it would "eventually" pitch down, just beware the "Garfield" (Alpha Prot) during the turbulent and hot conditions in this scenario because this may make things a little bit trickier.
Gary Lager,
I doubt people add to their Vapp because they are worried about reaching stall speed.
I add to Vapp often and that's for other reasons.
Remember Vapp = VLS+5 (or 1/3 of headwind component)
And when I see a discrepency between the Fac computation and fmgc I will manually correct this.
The problem is, that a reduced gap between Vapp and VLS on the PFD is due to a slightly over estimated gross weight in the FAC computation and therefore an overestimated VLS on the PFD compared to the FMGC VLS which is more accurate. For that reason in light headwind you can increase the managed Vapp to avoid having a small gap between the two "values".
Correct you don't stall by going below VLS but on the day with a bit of turbulence at the wrong time being below your VLS and your AOA limit is being reached you will get Alpha Floor and you are now in the middle of a go around.
In fact I have been told by a technical management pilot in EZY that they recommend you to use a minimum speed of Vapp+5 until a new retrofit of FAC is introduced.
I doubt people add to their Vapp because they are worried about reaching stall speed.
I add to Vapp often and that's for other reasons.
Remember Vapp = VLS+5 (or 1/3 of headwind component)
And when I see a discrepency between the Fac computation and fmgc I will manually correct this.
The problem is, that a reduced gap between Vapp and VLS on the PFD is due to a slightly over estimated gross weight in the FAC computation and therefore an overestimated VLS on the PFD compared to the FMGC VLS which is more accurate. For that reason in light headwind you can increase the managed Vapp to avoid having a small gap between the two "values".
Correct you don't stall by going below VLS but on the day with a bit of turbulence at the wrong time being below your VLS and your AOA limit is being reached you will get Alpha Floor and you are now in the middle of a go around.
In fact I have been told by a technical management pilot in EZY that they recommend you to use a minimum speed of Vapp+5 until a new retrofit of FAC is introduced.
The FAC computed speeds are only accurate to 3kts so there is no need to get `overanxious` about preserving the Vapp / Vls 5kt gap! In fact with manual thrust there is not even the requirement to add the 5kts - Vls is quite acceptable. The 5kt increment comes from the autoland and ATHR use requirements.
