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Flying in Turbulence on the A320

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Flying in Turbulence on the A320

Old 3rd Nov 2011, 16:56
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Question about flying in turbulence on the A320.

Dear gentlemen,

In my current outfit we fly the A320 and most of our CPT push the Mach/Speed pushbutton when we face turbulence conditions when flying in cruise. Do you guys, flying the Bus or any other jet, do the exact same thing?

I am a newbie but I don't feel it to be safe to fly IAS at (say) FL390... On the A320 you should fly 250KIAS up to FL200 and 275/.76 above that altitude. Once you pass the speed crossover why should you fly IAS?... The fundament this decision on (by flying selected IAS) the temperature will not be an extra factor on the change of Mach Number and therefore th flight will be smoother and more safe...

Any thoughts on this one? Did I manage to explain myself?

Thanks in advance.

Last edited by C212-100; 3rd Nov 2011 at 17:59. Reason: Change in title
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Old 3rd Nov 2011, 18:07
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I've done it before, but it has nothing to do with trying to smooth out the ride.

With "ALT CRZ" displayed on the FMA, the airspeed is allowed to fluctuate quite a bit. This is usually a good thing. But in turbulence, the speed will often go to the low limit, then thrust will surge, until you are up against the barber pole when thrust will decrease dramatically. THAT is actually unsafe. Pulling speed and selecting IAS forces the autothrust to maintain speed much more accurately.
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Old 3rd Nov 2011, 18:37
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Some 6 years since I flew the A320, but can't you enter a new Cruise Level in the FMGS which will then change 'ALT CRZ' to 'ALT' which also changes the A/Thr responsiveness, which is the fundamental issue?
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Old 3rd Nov 2011, 19:50
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Sure.

I think my technique might force the A/T to be even more responsive, but I haven't actually compared the two techniques.
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Old 3rd Nov 2011, 20:26
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jriv

I agree that your technique would work, and have indeed used it myself!

I was just pointing out an alternative method.

I remember trying to make a night curfew at TXL, and gettting direct to the OM from near the UK east coast. As I recall the A320 is very speed twitchy at M0.80 and above (Mmo 0.82), so we did use both techniques (ALT + IAS hold) which worked well - the Ground Engineer had left the destination assuming that we would have to divert to SXF, but we touched down with about 3 seconds to spare! Well worth the extra fuel burn.
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Old 3rd Nov 2011, 22:12
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From the FCOM.

"The soft altitude mode engages when the aircraft reaches the FCU altitude set as the cruise flight level (entered in the F-PLN or on PROG page).

The soft altitude mode corrects minor deviations from the Mach target by allowing a ​50 ft variation from the CRZ FL. This feature improves fuel efficiency and passenger comfort and minimizes the changes in thrust."

So by either going ALT (as opposed to ALT CRZ) or Speed from Mach you are effectively 'stiffening' up the response to BOTH Speed and Alt?

The speed control I can get, but surely a 50ft margin in turbulence might make it more comfortable and less stressful for humans and machine?

Interesting. I knew about soft alt but not about the speed/mach pb.

Cheers
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Old 7th Nov 2011, 10:03
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8 year on the bus, and I've never seen anybody do that yet.

sometimes I switch to SPD because I don't want to change speed as mucha s 6 knots.

I also play with speed and mach during the climb, for performance reasons.

I don't know if the A/THR is more responsive in speed than it is in mach. never heard of that. Any references?
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Old 7th Nov 2011, 10:35
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I use it often in turbulence on the A321. Our older 321s seem to be very sluggish with the Athr in Mach mode, so I will select speed and it holds the speed/Mach much more accurately.
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Old 7th Nov 2011, 13:53
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You could always take the A/THR out and set the numbers from the QRH.

mcdhu
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Old 7th Nov 2011, 20:43
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best thread I have seen in a while....
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Old 4th Jul 2012, 07:12
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The other day a line trainer on the A320 changed to IAS for keeping the A-thrust more responsive in the turbulent weather. Later I was checking the FCOMs, to confirm that the A-thrust is more responsive, but I can not find anything about this in there.

Anyone found something that proves this??

RG.
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Old 4th Jul 2012, 13:17
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don't know if the A/THR is more responsive in speed than it is in mach. never heard of that. Any references
Same on the 737 NG but i dont know the reason.
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Old 4th Jul 2012, 13:55
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side track

does the A320 have the turb penetration static N1 procedure like they do on the 330?

they say, in severe turb, to disco the A/T and keep the N1 at the recommended setting which is in the QRH (which supposedly is the thrust setting for turb penetration speed)
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Old 4th Jul 2012, 14:21
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Disconnecting A/T is always a good idea with turbulence approaching moderate.
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Old 4th Jul 2012, 14:44
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I believe that Soft Altitude Hold is only active when in Alt Crz and Managed Speed and I think it needs to have transited to Mach.

When you fly short relatively low sectors (below FL300) e.g. LHR MAN or even AMS the 320 doesn't go into Mach, it stays in speed (although in managed speed). Therefore Soft Alt Hold is not active with Alt Crz and Managed Speed.

In TX it is useful to simply pull the speed knob and use selected Mach, this takes it out of Soft Alt hold and the A/T will target the speed much better. Select .76 if it gets worse. In Soft Alt the speed can wander around a lot before the a/c reacts.

I press the mach/speed button sometimes as well to nudge the speed back a few knots rather than a whole mach number.

Last edited by wings11; 4th Jul 2012 at 14:48.
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Old 4th Jul 2012, 20:32
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my 2 cents answer...
the alt crz mode allows 50' change in altitude before actually moving any a/thrust setting
this is to relieve stress on the airframe and its contents...
you can disconnect it as well, setting the recommended turb n1...
meaning like 'don't touch anything in turbulence unless really needed'...
at higher altitudes fly mach i/o ias as a result of air compressibility...
meaning less a/thrust response for deviation unit,... thus more comfy ride.
happy landings all
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Old 4th Jul 2012, 22:13
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73driver...
same M number, different IAS
Pardon? I think you'll find that IAS and M have a fixed relationship - it's TAS that varies.
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Old 4th Jul 2012, 22:55
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never wanted to fly the bus...

just wondering...do you have a pitch control on your autopilot?

in the other jets I've flown, if there was turbulence, I would select PITCH and ride the waves.
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Old 5th Jul 2012, 01:00
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If turbulence makes altitude hold uncomfortable every jet manual I have read says fly attitude and ride it out. All aircraft fly about the same so don't think Airbus would be different than Boeing.
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Old 5th Jul 2012, 01:32
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Happy 4th of July to the USA people. We are now watching the fireworks across the bay with our grandkids. The 10 yr old girl has been blowing the conch shell for 15 minutes so came to the den to let my ears relax. Nice display of something very important to our people. I think it made a difference to the world too, but most won't admit it. WWll was a bit of a toss up in my opinion. Maybe without our support it wouldn't have ended up like it did. Now back to aviation talk.
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