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A320 OP CLB behaviour
Gents, yesterday as we were flying along at Vmax-5kt, I selected OP climb, and then rolled the speed back to something more reasonable for a climb, and Fifi reduced power to slow, then started climbing and added power. Only ever seen that happen once. Is there a system explanation that I’m missing? Did it do that simply because we were close to Vmax? |
Was it just a small climb? If the change is less that 1200ft it will do 1000ft/min |
Originally Posted by Inverted Flat Spin
(Post 10582568)
Was it just a small climb? If the change is less that 1200ft it will do 1000ft/min Recent convert to Airbus from Boeing here. It has it's oddities. |
It was a 5000ft climb. |
The autothrust is quite slow to react to changes, it probably targeted the lower speed first by reducing power and then realised you wanted to climb so it increased power. It's a 1980s design and can't keep up with even a modern smartphone. You would have been better off waiting until the aircraft was properly established in the climb before winding the speed back or managing it.
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Originally Posted by aerobatic_dude
(Post 10582614)
Have you an FCOM reference for this ?
Recent convert to Airbus from Boeing here. It has it's oddities. |
Originally Posted by Check Airman
(Post 10582543)
Is there a system explanation that I’m missing?
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Originally Posted by FlightDetent
(Post 10582629)
Nothing, it's the 5-year barrier. It happens, fuzzy logic.
I hope that doesn’t assume 900hrs a year. It may be more like a 10 year barrier for me! |
Originally Posted by Check Airman
(Post 10582543)
Gents, yesterday as we were flying along at Vmax-5kt, I selected OP climb, and then rolled the speed back to something more reasonable for a climb, and Fifi reduced power to slow, then started climbing and added power. Only ever seen that happen once. Is there a system explanation that I’m missing? Did it do that simply because we were close to Vmax? Yes. Fifi can be very exciting sometimes! |
Check Airman see below
Originally Posted by krismiler
(Post 10582619)
The autothrust is quite slow to react to changes, it probably targeted the lower speed first by reducing power and then realised you wanted to climb so it increased power. It's a 1980s design and can't keep up with even a modern smartphone. You would have been better off waiting until the aircraft was properly established in the climb before winding the speed back or managing it.
If you just leave the speed were it is, the a/c will raise the nose at max 1G, and the thrust will come on as required to maintain the target speed. Once established in the climb, with CLB thrust set, the desired climb speed can be set. Alternatively, if you need to start climbing asap, you can EXPEDITE (if fitted), and this will pitch to maintain Green Dot, therefore the thrust will increase sooner. I don't like this for a number of reasons: The pitch is aggressive for Cabin Crew and pax, and the speed decays very quickly. If you go below your desired Climb speed, it can be a struggle to get the aircraft to pitch down to regain it while continuing the climb. I have seen folks set a V/S initially too, and increase it as the thrust increases, before OP CLB, it works, but requires a lot more fiddling. My preferred method, if down low, i.e. 5000ft to FL100 ish, i.e.: On a SID with speed canceled, and expecting a climb soon, keep a bit of a buffer to Vmax, say 15-20kts. (290 works well, and conforms with SID design parameters) Then: Set the cleared Altitude, OP CLB INCREASE the target speed by 5-10kts. (This will initiate a thrust increase, as the a/c has already pitched for the climb, and you will have CLB THR and OP CLB) Set desired CLB speed target (I.e: Managed speed or en route climb speed) It gives a smoother transition to the CLB Thrust, and CLB attitude, also a larger buffer to Vmax, if you hit some bumps. (NOT TO BE USED IN THE HIGHER FLIGHT LEVELS) There is many ways to achieve the same thing, but the Airbus works in mysterious ways, this is the way i have found to manage this problem. Feel free to offer up other solutions. |
Jeez man, all this hoopla about advanced avionics and elegant user-friendliness, and reading this it looks like I have to hack into the Pentagon to start a climb!
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Hi Check Airman,
Did it do that simply because we were close to Vmax? There has to be a blend from AT controlling speed in ALT to Elevators controlling speed in CLM. Your speed intervention was done during the transition phase whilst AT was still controlling speed. |
Fun fact: at the same time the FMA will already tell you "climb thrust".
So in this case the FMA is obviously lying to you. But only for a few seconds.. |
Originally Posted by Farmer106
(Post 10582866)
Fun fact: at the same time the FMA will already tell you "climb thrust".
So in this case the FMA is obviously lying to you. But only for a few seconds.. |
Thanks all. I’ll try pay attention to exactly when I change the speed next time, to see what effect it has. One is always learning. |
The following information was released by Airbus in Sochi crash investigation:
The logic of integration of the autopilot/flight director (AP/FD) pitch control and the autothrust control ¬If AP/FD pitch mode controls a vertical trajectory (e.g. V/S, ALT), then AT controls speed. ¬If AP/FD pitch mode controls a speed (e.g. OP CLB), then AT controls thrust. ¬If no AP/FD pitch mode is engaged, then АТ controls speed. Logic sequence of the OPEN CLB mode ¬for level change more than 1200 ft: ¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = +8000 ft/min (40 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT ¬when engine N1 reaches 95% N1CLB mode, AP/FD switches to SPEED/MACH control law, whereas AT switches to the THRUST mode ¬Throughout this time the FMA displays THR CLB for AT and OP CLB for AP/FD The given scheme of engagement for the OPEN CLB mode ensures the uniformity of the aircraft response in all configurations and within the whole range of the flight altitudes and speeds. ¬For level change less than 1200 ft: ¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = + 1000 ft/min (5 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT ¬ Throughout this time FMA displays THR CLB for AT and OP CLB for AP/FD In this case the climb is in fact performed in the vertical speed control mode. *** It should also be noted that if the OPEN CLB mode is engaged less than 30 seconds after the aircraft level off function is activated, the autopilot is authorized to use the vertical acceleration at the maximum value of 0.3g, whereas usually it is only 0.15g. |
Hi Check Airman, Just out of interest and background, why were you climbing the way you were, and why were you not using Managed Climb? As some have said, Airbus FBW tends to try to operate smoothly, (unless you select TOGA). |
Originally Posted by Vessbot
(Post 10582751)
Jeez man, all this hoopla about advanced avionics and elegant user-friendliness, and reading this it looks like I have to hack into the Pentagon to start a climb!
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Originally Posted by ironbutt57
(Post 10583073)
..after it starts to climb, select any speed change you desire...
"when engine N1 reaches 95% N1CLB mode, AP/FD switches to SPEED/MACH control law, whereas AT switches to the THRUST mode ¬Throughout this time the FMA displays THR CLB for AT and OP CLB for AP/FD" |
Originally Posted by Uplinker
(Post 10583071)
Hi Check Airman, Just out of interest and background, why were you climbing the way you were, and why were you not using Managed Climb? As some have said, Airbus FBW tends to try to operate smoothly, (unless you select TOGA). To the question of managed vs open climb, I’m 50/50 on that. Most SIDs in the US don’t have altitude restrictions other than “at or above” (LAS and IAH are the only exceptions that come to mind) and if I recall, we may have been in HDG mode anyway. All else being equal, do people generally have a preference for managed vs selected? |
Originally Posted by vilas
(Post 10583003)
The following information was released by Airbus in Sochi crash investigation:
The logic of integration of the autopilot/flight director (AP/FD) pitch control and the autothrust control ¬If AP/FD pitch mode controls a vertical trajectory (e.g. V/S, ALT), then AT controls speed. ¬If AP/FD pitch mode controls a speed (e.g. OP CLB), then AT controls thrust. ¬If no AP/FD pitch mode is engaged, then АТ controls speed. Logic sequence of the OPEN CLB mode ¬for level change more than 1200 ft: ¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = + 8000 ft/min (40 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT ¬when engine N1 reaches 95% N1CLB mode, AP/FD switches to SPEED/MACH control law, whereas AT switches to the THRUST mode ¬Throughout this time the FMA displays THR CLB for AT and OP CLB for AP/FD The given scheme of engagement for the OPEN CLB mode ensures the uniformity of the aircraft response in all configurations and within the whole range of the flight altitudes and speeds. ¬For level change less than 1200 ft: ¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = + 1000 ft/min (5 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT ¬ Throughout this time FMA displays THR CLB for AT and OP CLB for AP/FD In this case the climb is in fact performed in the vertical speed control mode. *** It should also be noted that if the OPEN CLB mode is engaged less than 30 seconds after the aircraft level off function is activated, the autopilot is authorized to use the vertical acceleration at the maximum value of 0.3g, whereas usually it is only 0.15g. In the automatic flight, when the OPEN CLIMB mode was engaged, the aircraft started climbing rapidly, at a vertical speed up to 12 m/s, with pitch angle increased to 21º by 22:12:06, maximum vertical acceleration 1.27g, maximum angle of attack 10.7º, and the indicated airspeed reduced to 129 kt (240 km/h), which is 8 kt lower than the target speed. Engine r.p.m. were increased to the maximum possible value for the given position of the thrust control levers (Attachment 2, Fig.4). |
From Airbus FCOM: The managed climb speed, computed by the FMGS, provides the most economical climb profile as it takes into account weight, actual and predicted winds, ISA deviation and Cost Index (CI). The managed climb speed also takes into account any speed constraints, e.g. the default speed limit which is 250 kt up to 10 000 ft. A long time Airbus FBW TRE told us it was better to climb in managed if you can, and I think it was viewed as good practice. I always use managed climb/descent unless there is a good reason not to, (and just in case there is a constraint that I’ve forgotten). The only statement I can find for Open Climb: The OPEN CLB mode is a selected mode. It uses the AP/FD pitch mode to maintain a SPD/MACH (selected or managed) while the autothrust (if active) maintains maximum climb thrust. |
Uplinker, your first paragraph is referring to managed speed during climb. If you use open climb and managed speed you will get exactly the same economic climb profile as if you’d used managed climb and managed speed. |
Originally Posted by Uplinker
(Post 10583219)
From Airbus FCOM: . A long time Airbus FBW TRE told us it was better to climb in managed if you can, and I think it was viewed as good practice. I always use managed climb/descent unless there is a good reason not to, (and just in case there is a constraint that I’ve forgotten). The only statement I can find for Open Climb: Nothing about economy, but that’s not to say it doesn’t. The FCTM suggests not using managed climb unless you are flying constraints (PR-NP-SOP-150: FMS Use). OP CLB is to be used if ATC gives radar vectors or clears the aircraft to a give FL without any climb constraints. |
Originally Posted by giggitygiggity
(Post 10583244)
THR CLB/OP CLB uses a managed speed target which is whatever the CI asks for. As far as I know, THR CLB/CLB does exactly the same as OP CLB but uses the fmgc climb altitude constraints. The managed speed target remains the same regardless of whether it is open or managed climb. It will follow speed constraints in the flight plan as long as you’ve got the speed in managed. The FCTM suggests not using managed climb unless you are flying constraints (PR-NP-SOP-150: FMS Use). What you said is correct. But the reason for using OP CLB in unrestricted climb is rather obvious because in CLB it will level of at constraints and ATC is not going to like that. |
Originally Posted by vilas
(Post 10583278)
What you said is correct. But the reason for using OP CLB in unrestricted climb is rather obvious because in CLB it will level of at constraints and ATC is not going to like that.
As for the original topic, it seems to happen pretty consistently. If you’re in ALT with a high speed and pull for OP CLB, then wind the speed back, thrust rather inappropriately comes back. Not sure why this would be a ‘feature’ of the airbus though? I can’t find anything in the FCOM. If you select a higher speed then pull the speed back I think it keeps the thrust on like it should. |
Thank you vilas, that's epic!
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Originally Posted by vilas
(Post 10583003)
It should also be noted that if the OPEN CLB mode is engaged less than 30 seconds after the aircraft level off function is activated, the autopilot is authorized to use the vertical acceleration at the maximum value of 0.3g, whereas usually it is only 0.15g..
Also I have read on another post on Pprune that in CLB/OPEN CLB the G load will be max 1.1G and with expedite it will be 1.15G. Which differs quite a bit from your figures.
Originally Posted by giggitygiggity
(Post 10583318)
Like I said, the FCTM says you shouldn’t do it for the for those obvious reasons. I see lots of guys putting it back into managed climb if it reverts to open climb after finishing the SID. That and the guys using managed CLB when only 1000 feet to climb.. smh |
Our operator seems to love managed climb. If given unrestricted climb we will delete the restriction in the McDu in preference to using open climb. Our FCTM recommends CLB whenever we are in NAV. |
Originally Posted by AerocatS2A
(Post 10583606)
Our operator seems to love managed climb. If given unrestricted climb we will delete the restriction in the McDu in preference to using open climb. Our FCTM recommends CLB whenever we are in NAV. |
PR-NP-SOP-140
OP CLB is to be used if ATC gives radar vector or clears the aircraft direct to a given FL without any climb constraints. BUT The managed AP/FD mode in climb is CLB. Its use is recommended as long as the aircraft is cleared along the F-PLN. |
FCTM also states that below 10 000 feet, MCDU inputs should be restricted. I don’t think it is wise to go heads down at low level just to clear a constraint when you just have to select a knob on the FCU. |
My overall experience is that (managed) CLB is the standard and default mode. OP CLB only used when no choice (HDG) or actively wishing to ignore FMS altitude restrictions.
As if ATC gives radar vectors or clears the aircraft to a give FL without any climb constraints. I see the point that ironbutt and pinteam make, just in my area it is considered appropriate to have CLB instead of OPCLB when possible. Basic design philosophy:"all managed, all pushed". Check Airman I usually wait for "almost" full N1 before activating the climb to avoid that. BTW in your situation, I would had flown exactly the same modes, most likely forgetting and ending with the same result ("oh nintendo, was that really necessary?!"). Being a rather fully managed man myself, I do not consider operational choice of sel spd or V/S in busy airspace a sin. vilas I ran out of vocabulary praising you a long ago, but this one is a real diamond. |
FD, CA most welcome to share anytime anything
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Pineteam what I have posted is copy paste from Sochi investigation report and it's from Airbus. I had read it long time ago and only vaguely remembered luckily it's available on Google.
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I wonder what the plan is if they later give you the restrictions again.
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Golden Rules.
Originally Posted by Vessbot
(Post 10584018)
I wonder what the plan is if they later give you the restrictions again.
-oh. wait. I remember. Fly the Airplane.... |
Originally Posted by neilki
(Post 10584026)
Mutter expletive. Throw hands in air. Look confused. Look confused towards FCP. Transfer 'look of confusion' to FMC.
-oh. wait. I remember. Fly the Airplane.... |
Originally Posted by Vessbot
(Post 10584018)
I wonder what the plan is if they later give you the restrictions again.
Pulling the knob towards you tells the system, that you will decide how to fly the climb/descent, by adjusting the FCU. Pushing the knob towards the aircraft tells the aircraft to decide how to climb/descend, according to the data programmed into the FMGS. It’s really simple and an excellent arrangement.:ok: . |
Originally Posted by Uplinker
(Post 10584710)
Simply press the Alt knob and you will go back into Managed Climb. Seems to me like an absurd piece of makework. |
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