A320 Engine Anti-Ice, 1/2 speed brake and OP DES

[Bula]

Why the limit of 1/2 speedbrake? And only in OP DES...

[Founder]

FCOM Page reference please.

[bio161]

never heard about it.. :confused: could you please tell us in which FCOM you read this?
Thanks :ok:

[FatFlyer]

Hi,
my recollection is that A320 (not A319) limits speedbrake to half when autopilot engaged. (not sure if some specs differ)

FCOM says that using speedbrake in managed descent mode will not increase descent rate unless above profile ( as it tracking vertical profile)but I could not see that it is not allowed)

I wait to be corrected!

[shortfuel]

Hi Bula,

In the past, Airbus noticed that the full extension of speed brakes lead to activation of the AOA protection during EMER descent with AP ON and overshoot of VMO at speed brakes retraction with AP ON.

This was due to the limited AP pitch authority to counteract the pitch up moment at speed brakes extension.

Airbus modified SEC and ELAC standards fleetwide to introduce speed brakes deflection limitation with AP ON (half deflection) and pitch pre-command to nose up at speed brakes retraction.
So with AP ON with speed brakes lever to Full, you will always get half deflection (in OP DES or DES).

[PENKO]

On the 320. Can't be too clear about that :ok:

[jetjockey737]

When I moved from an 319 fleet to a 320 fleet this was something of a surprise to myself. The 320, with A/P engaged will only give 1/2 speedbrake. Some of our pilots only put the lever into the 1/2 position, I do not as I seem to think that will only give me 1/4 speedbrake....am I correct, I always put it into the full position if I want 1/2 or full...depending on how you look at it!!

[Alt Crz Green]

I think FatFlyer has it spot on: half speedbrake only is available on the A320 with the AP engaged (not the case for the 318, 319 or 321).

This is correct as regards to the 320 and 321 (I don't know about the other 2).
However, full speedbrake deflection on the A321 is the same angle of deflection as 1/2 speedbrake on the 320.
With AP engaged on the 320, speedbrake angle is proportional to the lever position until the 1/2 way detent. Thereafter any lever movement beyond 1/2 produces no change to the control surface position. Disengaging the AP allows full control of the speedbrakes, proportional to lever position.
On the 321, regardless of the AP condition, you have full control of the speedbrakes throughout the entire range of movement.

Some of our pilots only put the lever into the 1/2 position, I do not as I seem to think that will only give me 1/4 speedbrake

On the 320, this is not correct. With AP engaged, it is pointless moving the lever beyond 1/2 as 1/2 is all you will get. Remember, speedbrake deflection is proportional to lever position until 1/2, so by selecting 1/2, you will get 1/2, NOT a 1/4.
On the 321, if you selected 1/2, you would get 1/2 also, but as the angle of deflection range is only half that of the 320, in effect you would be getting 1/4 of the angle of deflection that would be available at full deflection on the 320.
Clear as mud....:bored:

[Metro man]

Full speed brake is available on the A319 with autopilot engaged however the panels only move to half of the position that they would on the A320.

Therefore an A320 with A/P engaged and half or full speedbrake selected = A319 with full speed brake.

We fly both types and the A319 doesn't slow down as quickly as the A320 on approach, some pilots need reminding that full speed brake is available with the A/P on, the halfway position has very ltttle affect.

Speed brakes may be used in DES mode, indeed the aircraft may call for MORE DRAG, typically when descent has been delayed and a speed or altitude constraint needs to be met on the way down. Needs to be watched carefully or you could be flying with brakes out and power on once the constraint has passed and you are back to profile.

I have been told that engine anti ice used on the A330 in descent may require the brakes due to the bump up in idle speed.

[shortfuel]

http://nsa22.casimages.com/img/2010/09/24/10092401380023263.jpg (http://www.casimages.com)

PS: there is a typo in this table, A320 should read 20/40/40° iso 20/20/40°.
In addition, A320 half deflection is 12.5/25/25°, so a bit more than just half.

[Bula]

Hey guys and gals,

thanks for the reply. The FCOM reference is FCOM 3.03.17 Page 3

SPEEDBRAKES................................................. ......AS RQRD

In OPEN DES :

Use speedbrakes to increase the rate of descent. The pilot may use up to half speedbrakes to maintain the required rate of descent, when engine anti-ice is used.



I thought it may have been a flight control law "g" issue resulting in an altitude overshoot or overspeed, but it seems to only apply with Engine Anti Ice on, and beside you have a .25g increase in pitch authority when speed brake is used. I think most of us have used Full Speed brake with OP DES and EAI without to much of an issue but I wonder if its a pitch attitude and icing issue. In other words, no idea.

Keep trying.. we'll get there sooner or later

[rudderrudderrat]

Hi Bula,

I believe it's only stating the drag of 1/2 speed brake is approximately equivalent to the extra thrust you get with Engine Anti ice selected on.

Simply use speed brake as required.

[Bula]

I thought it may have been a bit of franglai' ........

[ke_a320]

hi bula,
if you are in DES mode that means you are in a managed mode. the aircraft is keeping the calculated managed speed. In DES mode if you use the speed brakes, most probably the A/THR will compensate your loss of speed and will not be in the idle trust. So FCOM says to us: "if you wanna expedite your descent it is better to change your mode to OPEN DES mode. that's a selected mode and the aircraft will slow down. i hope that helps lately

[bond2002]

Can any one explane why in emergency decent on a A 320 full speed breake selection is done with autopiolt on.

[ke_a320]

when the autopilot is ON, you can't make a full speed brake selection. yes, you can select the speedbrake lever to be in full detent. but the system sure would limit the spoilers to half. (not exactly half). that's because ;

when it comes to a roll control function and a deceleration funtion, the roll function has the priority. so the system limits the deployment of the spoilers. In emergency descent you have to disengage the autopilot and select full speed brakes.

[shortfuel]

that's because ;

when it comes to a roll control function and a deceleration funtion, the roll function has the priority. so the system limits the deployment of the spoilers. In emergency descent you have to disengage the autopilot and select full speed brakes.

That's not the reason. You can find the main reason in my previous post above.
All other Airbus FBW will give you full speedbrakes deflection if you require so with AP ON, so the roll function priority is not the reason.
As for "having to" disconnect the AP during EMER DES...you state that as if that was the manufacturer procedure...not really.

[Togue]

FCOM DSC 27 10 20 Speed Brakes and Ground Spoilers.

[neilki]

That's not the reason. You can find the main reason in my previous post above.
All other Airbus FBW will give you full speedbrakes deflection if you require so with AP ON, so the roll function priority is not the reason.
As for "having to" disconnect the AP during EMER DES...you state that as if that was the manufacturer procedure...not really.
Tried Full Speedbrakes in a 321 today.. Didn't slow down any faster, but its a very reassuring rumble....

[AerocatS2A]

Hey guys and gals,

thanks for the reply. The FCOM reference is FCOM 3.03.17 Page 3

SPEEDBRAKES................................................. ......AS RQRD

In OPEN DES :

Use speedbrakes to increase the rate of descent. The pilot may use up to half speedbrakes to maintain the required rate of descent, when engine anti-ice is used.



I thought it may have been a flight control law "g" issue resulting in an altitude overshoot or overspeed, but it seems to only apply with Engine Anti Ice on, and beside you have a .25g increase in pitch authority when speed brake is used. I think most of us have used Full Speed brake with OP DES and EAI without to much of an issue but I wonder if its a pitch attitude and icing issue. In other words, no idea.

Keep trying.. we'll get there sooner or later

Don’t over think it.

I don’t have the same style of page reference as you, however my FCOM has the following in plain English and all it is saying is that you may need some speedbrake to counter the higher flight idle caused by engine anti-ice on.

If engine anti-ice is selected in descent, the flight idle is increased. So, to maintain the rate of descent that the airplane had before engine anti-ice selection it may be necessary to use up to half speedbrakes to maintain the required rate of descent, in OPEN DES vertical mode. If the rate of descent has to be increased, full speedbrakes may be used. In DES mode: If the aircraft is on, or below, the flight path and the ATC requires a higher rate of descent, do not use speedbrakes because the rate of descent is dictated by the planned flight path. Thus, the A/THR may increase thrust to compensate for the increase in drag. In this case, use OPEN DES with speedbrakes.

[Bus Driver Man]

I thought it may have been a bit of franglai' ........
Exactly. It's just a poor translation.

[Bus Driver Man]

Can any one explane why in emergency decent on a A 320 full speed breake selection is done with autopiolt on.
Because your airline might be operating A319, A320 and A321. The emergency descent memory items are the same for all variants: Select full speed brake during an emergency descent, regardless whether or not it will give you full or only half speed brakes and regardless which variant you are flying. Also in case of CCQ it will be the same memory items on all types.

[pineteam]

if you are too high, running out of options and don’t wanna extend the gears, AP off with full speed brakes give you a nice ROD. Very useful in times of non expected shortcuts. Worth a try.

[FlightDetent]

There is a full eight year difference between posts #17 and onwards, just saying.

The notion about different g load commands wit EAI sounds weird.

[AerocatS2A]

Oops, a zombie thread, risen from the dead! BRAINS!