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-   -   Selected Speeds on A320 (https://www.pprune.org/tech-log/600379-selected-speeds-a320.html)

Boyington 5th Oct 2017 16:54

Selected Speeds on A320
 
Why is it that even the VApp is SELECTED in case of failures like Dual hydraulic and Slats/Flaps jammed in the A320.

fpuentegomez 5th Oct 2017 18:17

I'm only speculating here, but it could be due to the fact of being a high workload situation for the pilot flying, in such case a fixed selected speed is less workload than following a managed target affected by GS MINI.

Sciolistes 5th Oct 2017 18:20

To reduce speed, sometimes below maneuvering speed to avoid over speed,or to only reduce speed once the flap is extended and to ensure minimum speeds are maintained when going around or diverting.

Sidestick_n_Rudder 5th Oct 2017 21:46

Also because the approach and maneuvering speeds with partial flaps/slats can be different than the FMS target speeds - and the FMS might not necessarily know it.

Bottom line: non standard config - non standard speeds have to be used.

vilas 6th Oct 2017 04:45

Boyington is asking why Vapp also flown selected when it can be easily flown managed since we have corrected it in MCDU.fpuentegomez seems to have given logical answer

sierra_mike 7th Oct 2017 22:04

i don't see any wording explicitly prohibiting the use of GS mini in mentioned cases once you're in LDG config given VAPP is amended accordingly in MCDU

KingAir1978 8th Oct 2017 02:24

Because the autothrust system will not allow the speed to decrease below the manoeuvring speed, if you keep the speed managed.

If you have the flaps stuck at 1+f for example, you'll need flap lever position 2 for landing. (to get the slats extended in position 2) The calculated Vapp will be lower than the manoeuvring speed, so it needs to be selected.

Boyington 8th Oct 2017 02:49

What exactly do you imply by manoeuvring speed? Do you mean VLS? Thanks.

Chrome 8th Oct 2017 05:36

F and S speeds are manoeuvring speeds.

Check out the abnormal procedure from the FCTM as it is also explained there.

vilas 8th Oct 2017 05:51

sierra_mike

i don't see any wording explicitly prohibiting the use of GS mini in mentioned cases once you're in LDG config given VAPP is amended accordingly in MCDU
Since the QRH recommends use of select speed it takes out the GS mini out of equation. No need to expressly ban GS mini.
KingAir1978

Because the autothrust system will not allow the speed to decrease below the manoeuvring speed, if you keep the speed managed.
If you have the flaps stuck at 1+f for example, you'll need flap lever position 2 for landing. (to get the slats extended in position 2) The calculated Vapp will be lower than the manoeuvring speed, so it needs to be selected.
What you are saying is exactly opposite of what happens. S and F speeds come from flap lever position and not actual surface. So with flaps jammed at 1+F if you move the lever to position two the speed will come down to F which will be unsafe because one of the surface hasn't extended and that is why you use select speed. But the question asked is after you have configured to Vapp why can't the rest of the approach be flown in managed speed?

Cough 8th Oct 2017 09:00

Been a while since I was on the Bus, but...

I always understood a part of the reason for using selected in these instances was due to the fact you were in direct law for landing hence had no autotrim. As GS mini oscillates the speed around the workload is going to increase for the PF as he has to retrim for each change in speed, which isn't something which is regularly practiced on the Bus... Nor is convenient if you are in manual thrust too..

sierra_mike 8th Oct 2017 10:38


Since the QRH recommends use of select speed it takes out the GS mini out of equation. No need to expressly ban GS mini.
my current QRH only mentions to select VFE-5kt in order to configure safely. once in LDG config i don't see the procedure speaking against managed speed. purely speaking about being in LDG config, no question about the other phases.
since we use managed SPD for landing in normal daily ops i would expect airbus to explicitly tell us not to use it if they don't want us to. i.e. as they do for overweight landing procedure "SPEED AT RUNWAY THRESHOLD: VLS"

vilas 8th Oct 2017 12:07

Cough
I think in direct law to stay in trim for a fixed Vapp speed is a very valid point. However the new QRH creates an impression that managed speed can be used at Vapp. It only says decelerate to calculated Vapp.
sierra_mike
As you correctly noted there are some changes to Landing with slats or flaps jam QRH procedure. Following notes have been deleted:
1. Use of selected speed is recommended.
2. Autopilot may be used down to 500ft AGL.
3. ATHR is recommended except B+G LO PR warning.
However in VLS greater than VFE next case is retained which can be interpreted as ATHR can be used. Below from QRH:
If VLS is greater than VFE NEXT (overweight landing case), the FLAPS lever can be set in the required next position, while the speed is reduced to follow VLS reduction as surfaces extend. The VFE warning threshold should not be triggered. In this case, disconnect the A/THR . A/THR can be re-engaged when the landing configuration is established.

sierra_mike 8th Oct 2017 15:06


If VLS is greater than VFE NEXT (overweight landing case), the FLAPS lever can be set in the required next position
true that vilas! i have the impression that i might not have expressed myself clearly before with


since we use managed SPD for landing in normal daily ops i would expect airbus to explicitly tell us not to use it if they don't want us to.
what i meant: if airbus doesn't want us to touchdown with a managed speed target utilizing GS mini (as we normally do) they would specifically point it out as they do for example in the overweight landing procedure "SPEED AT RUNWAY THRESHOLD: VLS"

LHRPony 9th Oct 2017 08:59


Originally Posted by Chrome (Post 9917935)
F and S speeds are manoeuvring speeds.

Check out the abnormal procedure from the FCTM as it is also explained there.

Chrome,
Unless our fcom's ar different, F &S are min speeds for retraction not manoeuvring. Pro sup 10

VLS is however a manoeuvre speed. 1.13 vs after take off, 30 degree bank turn stall speed increase is approx 1.08,
1.23 vs after retraction of 1 stage, 1.28 vs clean
Stall speed increase for 45 degree bank is 1.19, so you've got at least 30 bank avail + 15 over bank at VLS

vilas 9th Oct 2017 12:28

I stand corrected. According to Airbus they are manoeuvre speeds but not limitations. It is safe to fly between VLS and Vmax (VMO, VLE, VFE). The required aerodynamic margin is properly ensured. Also in Slat/flap jam Autopliot use upto 500ft. is relocated and not removed.

Chrome 13th Oct 2017 20:22


Originally Posted by LHRPony (Post 9919013)
Chrome,
Unless our fcom's ar different, F &S are min speeds for retraction not manoeuvring. Pro sup 10

Hi LHRPony,

Taken from the FCTM that I have;
Abnormal Flaps/Slats Configuration
Failure During The Approach
... With A/THR operative, the managed speed target will become the next manoeuvring characteristic speed e.g. S speed when selecting flap lever to 1...

CaptainMongo 14th Oct 2017 02:42


Originally Posted by vilas (Post 9919216)
I stand corrected. According to Airbus they are manoeuvre speeds but not limitations. It is safe to fly between VLS and Vmax (VMO, VLE, VFE). The required aerodynamic margin is properly ensured. Also in Slat/flap jam Autopliot use upto 500ft. is relocated and not removed.

My motto is, "I wish I knew what I wish I knew."

I am a huge fan of this forum. It is one of the very few places on the sewer of the internet where fresh water is available.

Vilas, as a 319/320 pilot, Captain, and Line Check Airman, I always have put great value into your input into this forum. Your correction only adds to that value.

vilas 14th Oct 2017 11:55

Thanks mate!

LHRPony 14th Oct 2017 15:31


Originally Posted by Chrome (Post 9924232)
Hi LHRPony,

Taken from the FCTM that I have;
Abnormal Flaps/Slats Configuration
Failure During The Approach
... With A/THR operative, the managed speed target will become the next manoeuvring characteristic speed e.g. S speed when selecting flap lever to 1...

Cheers Chrome,
So we have fcom defining they are retraction speeds, fctm saying they are man speeds.
Genuine question, what manoeuvre margin exists at the f and S? it's defined for VLS,but I haven't come across any definition for manoeuvre margin for f and s.
And not wishing to get into a tit for tat, it does also say if their is a discrepancy between fcom and fctm then fcom takes precedence.
But as always happy to be corrected.
Thanks for your input, always good to rattle these things around and see where we end up.


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