A320 OP CLB behaviour
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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).
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:
.
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 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.
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.
.
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.
Last edited by giggitygiggity; 30th Sep 2019 at 17:20. Reason: aerocat sniped me
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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).
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.
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.
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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.
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.
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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.
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.
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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.
Only half a speed-brake
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
meant when ATC tells you to ignore those 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.
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.
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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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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.
.
Last edited by Uplinker; 2nd Oct 2019 at 19:04. Reason: Typo
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