A321 speedbrake and flaps 2

[Speedwinner]

Hi guys,

Could someone explain me the following fact?

When flying with flaps 2 and putting the speedbrake out in a A321 you always get a roll moment. To the left and then to the right. Short term and then it’s gone. You don’t have that on the 320 or 319. What is the technical reason?

Thanks!

[applecrumble]

As the speedbrakes extend it causes a very slight difference in airflow over each wing which induces the rolling motion that you speak of. It can also occur on the A320.
This is why speedbrakes and FLAP 2 is not reccomended by Airbus.

[Killaroo]

Also consider that with speedbrakes stowed (flush) any roll demand generates some deployment of spoilers - on one side only, whereas with speedbrake deployed (say, halfway) a roll demand results in partial retraction of spoilers on one side and further deployment on the other. I'm sure the whizzo computers adjust the effect to some extent, but the added sensitivity is still noticeable, especially in turbulence with the autopilot working harder to maintain wings level. The book says 'not reccomended' but it is not a prohibition, and in certain conditions it may be the better solution (as opposed to early gear extension for instance).

[oicur12.again]

"This is why speedbrakes and FLAP 2 is not reccomended by Airbus"

Got a reference for this?

[FlightDetent]

^^ seconded. Last time I checked F2 + SPDBRK was one of the recommended configurations on approach.

[Killaroo]

I’m referring to A330 FCOM, but I’d presume the same applies to any of the Airbus family.
I can’t be arsed to dig out the reference now but know it’s there because I was challenged about in in a Line Check debriefing a few years ago. The wording said “not recommended” but not “prohibited”.

[FlightDetent]

3810

3811

[mcdude]

Worst misinterpretation of FCOM and the original thread question I've seen!

[applecrumble]

Straight from Airbus my friend. Argue all you want.

[applecrumble]

If there is no failure and warning on aircraft related to this issue, this is likely the result of the aerodynamic phenomenon described here below and referred to in FCOM 3.03.18 P.5.
When the flaps start to extend while the speedbrakes are extended, the airflow around the wings transiently changed and this transient change is not exactly the same on both wings.

Model: Manufacturer:
First Issue Date: 16-SEP-2009 Last Publication Date: 15-OCT-2012
This transient lift asymmetry between left and right wings induces a slight roll movement.
This phenomenon is an inherent consequence of the aircraft aerodynamics and mechanical characteristics and used to be observed always in the same direction on one given aircraft.
This phenomenon was assessed during flight tests campaign and found operationally acceptable, as it affects neither the manoeuvrability nor the performances of the aircraft.
Note that same behaviour can also be reported when the speed brakes start to extend while the flaps are in configuration 1+F or 2.
In this scenario, no maintenance action is deemed necessary.

[charlies angel]

Applecrumble.

The FCOM is saying it does not recommend speed brake to further reduce the speed as you will be slow speed (reducing to F Speed ) at Flap2 anyway and the airbrake is fairly ineffective for speed reduction.

Therefore dropping the gear will be far more effective in reducing energy.

The following statement ref slight oscillations is just a statement of a known Airbus software bug NOT a reason for not taking speedbrake with flap 2.

[Killaroo]

RWY25R at HKG, base leg at 8,000ft with speed control 180kts, requiring F2.
The usual is a corner cut direct to the LOC, which puts you above the GS. Maybe with a tailwind too.
At 8,000ft your ideal distance to touchdown is 24 miles, maybe you’re at 22 now and descending to intercept the GS.
You can take the gear and be back on GS almost instantly - then drag it in for the next 20 miles. Or, you can take half speed brake and drift down onto the GS at 180kts, then stow them when sorted out.
The FCOM comment is not a prohibition and it’s a better solution for pax comfort, noise, and fuel.

[charlies angel]

Killaroo
Agree entirely:ok:
Nearly the most fun you can have in an Airbus 320 is Flap 2 FULL Speedbrake.
Going back in time now. A320 only gives half speedbrake with autopilot on and full with autopilot disconnected ( unlike A321 which is full range A/P in or out )
Used to fly a sub msn 100 A320 that used to drop its port wing so badly with F2 and full speedbrake we used to disconnect the autopilot and the wing drop would take you onto final vector for the localiser.

[oicur12.again]

As mentioned above, the F2 plus speedbrake issue is concerning the transient accel that can occur during extension on a fixed path. The slight role is not the issue.

[pineteam]

I’m with Killaroo and Charlies Angel. flaps 2 with Speed brakes work beautifully and will bring down the aircraft faster than with conf 1 + speed brakes. If you are on glideslope already and concerned about overspeeding , gears down might be a better idea.

[FlightDetent]

Similar understanding here. From the FCOM pages posted above:

[my wording]
1+F and real faster than S:
- use the speedbrakes at will,
- seriously think about extending the L/G

F2 and real faster than F:
- drop the wheels!
- forget about the speedbrake

The above sounds to me like an operational requirement, an advice how to get the job done quickly and effectively, using the proper tools available. Also to remove false hope that SPD with F2 well above F speed actually achieves much. That's why it is in FCOM I guess, and not in AFM.

The other line about uncorrected bank with F2+SPD stands separate, just a heads up about a F/CTL quirk.

Interestingly I've learn through the run of this thread that the FCTM G/S from above technique is F2+L/G, I had wrongly believed it is F2+L/G+SPDBRK:half.

F2+L/G+AP:off+SPDBRK:full does indeed work maybe too well. :) On every of the few occasions when done, I wish to had been smarter several minutes before and avoided / never created the need for it in the first place. Decribing it as "thrilling" instead of "fun" would be my choice of words, "unsetteling", "eye widening", "massive aggressive" maybe too.

Anyone who hadn't tried yet (good): be cautious to stow them and add thrust early enough before coming onto the desired 3 deg profile. Extremely cautious.

[vilas]

There is only caution for flaps2+speed brake below 2500 on GS, as gear will have to be taken better to do little early. A330 speed brake is not inhibited even in flaps full.