A320 Preselected climb speed lower than Green Dot

[J.L.Seagull]

Hi guys...

Just wondering what happens if you have a heavy aircraft, and Green Dot speed in clean config is higher than the preselected speed on the PERF CLIMB page.

e.g. some SID's require to fly 220kt, but the GD could be as high as 235kt. If you leave the speed managed, what will the aircraft fly?

[vilas]

Two things. First, normally after flap retraction default speed target is 250 so if you go manage it will accelerate to 250 if you want different speed you will have to use preselect or change the default speed below 10000ft. by vertical revision. Second, it is permitted to fly beow green dot speed all speeds upto VLS are flyable, only the bank angle at which ᾳ floor gets activated gets lowered from 45 degrees to 40 degrees. In turbulence the margin could be less.

[EGPFlyer]

If you need to fly 220, why not keep the flap out?

[John Citizen]

Just wondering what happens if you have a heavy aircraft, and Green Dot speed in clean config is higher than the preselected speed on the PERF CLIMB page.

The aircraft will fly the preselect speed on the PERF CLIMB page, even if below green dot. (or maneuvering speed of the current slats/flaps configuration - F, S, Green Dot)

FCOM 1 DSC-22_30-40 speed/mach control :
Note: The selected speed/Mach target may be set beyond VLS or VMAX, but when autothrust is active, the guidance limits the speed to VLS or VMAX.
Selected speed has priority over managed speed

e.g. some SID's require to fly 220kt, but the GD could be as high as 235kt. If you leave the speed managed, what will the aircraft fly?

If you leave the speed managed and retract the flap, I believe the aircraft will fly GD speed (235 knots) even if 220 knots is a speed constraint in the SID.

FCOM 1 DSC-22_30-40 speed/mach control :
The managed speed/Mach target may be set below maneuvering speed but
as long as the speed target is managed, the FMGS limits the aircraft to the
maneuvering speed of the current slats/flaps configuration (VAPP, F, S, Green
Dot).

[John Citizen]

e.g. some SID's require to fly 220kt, but the GD could be as high as 235kt. If you leave the speed managed, what will the aircraft fly?


If you leave Flap 1 out (as someone already advised), then it will fly 220 knots in managed speed (if the 220 is a speed constraint in the SID).

Accelerating through 210, the flaps will auto retract and only the slats will be remain out (change from conf 1+F to conf 1).

[J.L.Seagull]

Thanks JC!

I was being a but lazy, but also a bit hare-brained. Didn't know where to look for the answers in the FCOM.

I wasn't looking for advice on how to fly the SID, but really asking about the aircraft behavior, and you really nailed it for me! :)

So, as I understand it, if you enter a pre-selected speed on the PERF CLB page, that's exactly what she will fly, regardless of green dot, or flap position. (with all other protections still applicable, e.g. VLS, auto flap retract, etc)

AND, if you leave everything managed, it will go to a) 250kts if there are no other constraints, or b) either GD or the SID constraint speed, whichever is higher.

Thanks for your help.

[IcePack]

Sometimes a 1+F take off with say an S speed of around the 210 mark ie heavy. BUT a SID req speed of 180. Does cause problems especially if company SOP's are to fly S (or F or Gdot) only.
But as has been reported Airbus are happy as long as the speed remains above VLS.:ok:

[Rocket3837]

Seagull

If you preselected 220 kts prior to departure, the managed speed during takeoff and initial climb will automatically change to selected speed (220) at ACCL ALT.
Now if you push speed knob, the speed will go managed (250 kt).

[IcePack]

Unfortunately no performance for that. You can't just select your flap setting out of a hat.
Only happens occasionally.

[Cough]

Don't forget 'S' relates to Flap 1. You have 1+F so have a greater margin than in the slats only config.