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cgentil

Speed brake still out master caution

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Hi,

 

Guys there seem to be any problem with master caution about speed brake.

 

For example if we have speed brakes full and speed at 250 and want to reduce to 200, it always shows master caution with speed brake still out and the speed is still trying to decrease.

 

It is normal behaviour?

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This is the initial thing, no speed brakes.

 

6cd8753e2875e8199eadc5e9b9779941.jpg

 

With speed brakes:

 

bd5b2fef273c3f71b17ae8c1daa90173.jpg

 

52713e430bbcb21c8ed013f68c905739.jpg

 

 

2ff074b955203b098b4aaff84a7d304e.jpg

 

And it continues always....

 

PS. AFAIK the speed brake spelling should be "SPEED BRK" for both amber and green and not "SPD BRK".

 

fa1703e2e06874987b246a8cc51c551f.png

 

PS2. Ok, just double checked the FCOM and it says.

 

7fc8d3ce293d76f6b1d31c830a010446.png

 

Well it looks it is correcly modelled, so we should only use speed brakes when engines are IDLE?

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The "Speedbrake still out" message and chime occurs when the speedbrake is extended with thrust >idle.

 

I have noticed that in managed descent the thrust can occasionally fluctuate slightly above idle on occasion when on or above profile, resulting in an intermittent chime and "Speedbrake still out" ECAM. In Open Descent the thrust remains solidly at idle, however, and so no such messages appear.

 

I am not sure whether the Managed Descent behaviour is accurate or not: my suspicion is not, however.

 

If you are in level flight, wind the speed back from 250kt to 200kt and whack the speedbrake out, you may get the chime and message if the thrust has not reached idle (without checking the books, I am not sure whether the message is triggered based on actual or commanded level of thrust, however). Likewise if you are approaching 200kt still in level flight and the A/THR starts increasing thrust to capture the selected speed, you will get the message (quite correctly).

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Iv noticed this myself I wasn't sure if it's a bug, iv also seen this issue after 01:40 minutes into this video, before 01:40 the chime seems to be alerting normally but after 1:40 (I may be wrong) the chime seems to be alarting too early and too frequent although the weather seems a bit bumpy in the video so the frequent part may be disregarded. 

 

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On 10.1.2016 at 6:43 PM, cgentil said:

we should only use speed brakes when engines are IDLE?

 

Take a little time to think about this Chirag.
What do the speedbrakes do and what do the engines do?
The speedbrakes slow your engine down and disrupt airflow, thus causing a loss of lift.
The engines effectively do exactly the opposite, they accelerate you and thus create more lift.

 

Notice something? :)

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16 minutes ago, Emanuel Hagen said:

 

Take a little time to think about this Chirag.
What do the speedbrakes do and what do the engines do?
The speedbrakes slow your engine down and disrupt airflow, thus causing a loss of lift.
The engines effectively do exactly the opposite, they accelerate you and thus create more lift.

 

Notice something? :)

 

Certainly this is not required for any Airbus aircraft, but while decending through icing conditions with engines at idle, it is a well-established procedure on the MD80 (and maybe other older jets) to pop out the speed brakes to have the engines rev up in order to create sufficient bleed air pressure for the de-icing systems to work properly.

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Correct, this is not required for the Airbus. The fadec does that automatically. It is even modeled by AS. Just idle the engines and switch on engine anti ice and watch what happens to the idle value.

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55 minutes ago, The Dude said:

Correct, this is not required for the Airbus. The fadec does that automatically. It is even modeled by AS. Just idle the engines and switch on engine anti ice and watch what happens to the idle value.

 

Yep. I already noticed this quite some time ago with a smile. Nice and essential detail.

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4 hours ago, 320Ski said:

Iv noticed this myself I wasn't sure if it's a bug, iv also seen this issue after 01:40 minutes into this video, before 01:40 the chime seems to be alerting normally but after 1:40 (I may be wrong) the chime seems to be alarting too early and too frequent although the weather seems a bit bumpy in the video so the frequent part may be disregarded. 

 


Notice the FMA is occasionally flicking in to SPEED from THR IDLE. Although the actual thrust level isn't increasing appreciably, I'm guessing the fact that the A/THR is bringing the thrust lever "off the backstop" (in a virtual sense) is sufficient to generate the message. This seems to be an issue with descents in "speed on thrust" modes such as V/S and DES (managed).

 

Assuming the real thing doesn't flick in to SPEED mode quite so frequently (especially when above speed/profile) I would imagine the fixes would be either a tweak of the A/THR model -- or, assuming that might mess up other aspects of the A/THR, it might be possible to bodge the SPEED BRK STILL OUT message so that it requires a more significant level of thrust before displaying to prevent transient nuisance messages like yours above.

 

(PS, landing tip: the reason you floated is that the A/THR put in a squirt of thrust as you flared (raise nose, speed drops, A/THR corrects). If you start (slowly) pulling the thrust levers at around 50ft, by the time you get to the flare you should have more or less matched the thrust lever position with the actual commanded level of thrust. Because the A/THR will only command thrust up to the thrust lever position, by doing this you should prevent it from giving you that destabilising burst of thrust in the flare, and as you further reduce the thrust to idle, combined with a very slight increase in nose attitude, you will gently plop on to the runway).

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10 minutes ago, skelsey said:


(PS, landing tip: the reason you floated is that the A/THR put in a squirt of thrust as you flared (raise nose, speed drops, A/THR corrects). If you start (slowly) pulling the thrust levers at around 50ft, by the time you get to the flare you should have more or less matched the thrust lever position with the actual commanded level of thrust. Because the A/THR will only command thrust up to the thrust lever position, by doing this you should prevent it from giving you that destabilising burst of thrust in the flare, and as you further reduce the thrust to idle, combined with a very slight increase in nose attitude, you will gently plop on to the runway).


This won't work, in the Airbus the thrust levers only command the maximum thurst A/THR may add if the A/THR is activated.
Thus slowly reducing the thrust levers from 50ft on won't have any effect on the actual thrust until you pass roundabound the 60% N1 marking which will likely only happen when you reach the 20ft where the A/THR starts reducing the thrust anyway.

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2 minutes ago, Emanuel Hagen said:


This won't work, in the Airbus the thrust levers only command the maximum thurst A/THR may add if the A/THR is activated.
Thus slowly reducing the thrust levers from 50ft on won't have any effect on the actual thrust until you pass roundabound the 60% N1 marking which will likely only happen when you reach the 20ft where the A/THR starts reducing the thrust anyway.

 

Exactly. That's my point: as you pull the thrust levers back from 50ft you're not (shouldn't be!!) having any effect on the actual commanded thrust level, but you are limiting the A/THR capability to give you a nasty surprise. The A/THR is still active (even if not doing very much) until you hit the idle stop, of course (which ideally you want to be hitting at around 20 feet, so the engines are then spooling down in the flare).

 

Edit to add: if you wait for the "retard" callout to chop the thrust, firstly you will tend to get an unwanted extra squirt at around 20-30ft, and secondly the engines don't get a lot of opportunity to spool down (which takes some time). I should clarify I'm not advocating initiating the flare at 50ft or anything like that, which is asking for trouble: flare height (and, actually, the actual thrust reduction) is normal, it's just a way of ensuring that the thrust really does come off when you want it to.

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On 15 January 2016 at 10:17 AM, Emanuel Hagen said:

 

Take a little time to think about this Chirag.
What do the speedbrakes do and what do the engines do?
The speedbrakes slow your engine down and disrupt airflow, thus causing a loss of lift.
The engines effectively do exactly the opposite, they accelerate you and thus create more lift.

 

Notice something? :)

lool

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Because we believe this topic has been answered we have closed it. If you have any more questions feel free to open a new topic.

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