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A320 slow spool-up

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A320 slow spool-up

Old 21st Mar 2014, 21:00
  #1 (permalink)  
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Join Date: Nov 2004
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A320 slow spool-up

Good morning,
I had a strage engine behaviour the other day, and i can't find reference in any manual. It's not the first time it happens, but i cannot replicate it if i wanted

Start situation
-CFM engines
-8000ft SPEED/ALT/NAV
-IAS 255kts approx, with spd selected 250
-N1 approx 40 to 50%

I have been cleared to FL 200 so, selected and pull
-FMA THR CLB/OP CLB/NAV

Still the engine stayed at the same N1 (i am not sure, but i believe the actually even spooled down a bit)

After few -very long- seconds, engines spooled up to CLB THR and everything started working normally again
I am aware of the FCB9 "THRUST ACCELERATION IN A/THR MODES", but this is not the case (as the engine where no spooling up at all)

I looked for references in the FCOM, but i can't find any to explain this behaviour

Any thoughts?

Thanks in advance
Tiennetti is offline  
Old 21st Mar 2014, 21:23
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Join Date: Feb 2006
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A320 slow spool-up

Hi, I know the behaviour you speak of, I'm not sure why it happens but next time it does, you can force the engines to spool up quickly by winding the selected speed up by 10 or 15 knots.
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Old 21st Mar 2014, 21:27
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Thanks Shunt, a previous time it happened i forced the spooling by putting the airplane in V/S
But i am curious to know "Why is doing that" (recurrent question while flying airbus....)
Tiennetti is offline  
Old 21st Mar 2014, 21:53
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A320 slow spool-up

Cant the question be referred to airbus or engineers?
Pilot.Lyons is offline  
Old 21st Mar 2014, 22:12
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IIRC, we first noticed this behaviour over 25 years ago!

Although the FMAs have changed to CLB/OP-CLB, the A/THR does not change instantly from SPD mode to thrust (CLB) mode. This is probably to give a smoother transition from ALT to OP-CLB (less G) for the benefit of the pax and standing cabin crew.

As SHUNT says, if necessary you can get the engines to accelerate immediately to climb N1 by selecting a higher IAS than the current IAS, and then reducing it. Or, if you're not worried about pax comfort, you can go for EXP-CLB temporarily (if still fitted?).

Enjoy!
Chris Scott is offline  
Old 21st Mar 2014, 23:38
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Join Date: Jul 2000
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My favourite trick...

FMA says 'THR CLB, OPEN CLB'. EWD shows 'IDLE'....

My best is having the engines wind up over 3,500' climb!

But I can't write anything better than Chris, so I'll sto
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Old 22nd Mar 2014, 11:47
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Thanks Chris, but the airplane is not behaving like this every time... so i will understand your reasoning
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Old 22nd Mar 2014, 13:11
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Tiennetti
Since your actual speed is higher than selected may be first it is trying to get to the correct speed and then maintain it with pitch up and climb thrust. Hence the delay in CLB THR. Next time try the climb at correct speed and see what happens. Also the pitch changes in Airbus are executed at 1G for comfort.
vilas is online now  

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