A320 OP CLB behaviour
Thread Starter
Join Date: Mar 2006
Location: USA
Posts: 2,514
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?
Join Date: Feb 2005
Location: BNN, OCK =)
Posts: 64
Likes: 0
Received 0 Likes
on
0 Posts
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.
Only half a speed-brake
Thread Starter
Join Date: Mar 2006
Location: USA
Posts: 2,514
Likes: 0
Received 0 Likes
on
0 Posts
Ha. Thanks FlightDetent
I hope that doesn’t assume 900hrs a year. It may be more like a 10 year barrier for me!
I hope that doesn’t assume 900hrs a year. It may be more like a 10 year barrier for me!
Join Date: Sep 2007
Location: New York
Posts: 225
Likes: 0
Received 0 Likes
on
0 Posts
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?
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
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.
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes
on
0 Posts
Hi Check Airman,
No. Unlike ALT* which is annunciated, the transition from ALT to CLB is annunciated immediately - but it can't be so.
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.
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.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,404
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Last edited by vilas; 1st Oct 2019 at 15:43.
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).
As some have said, Airbus FBW tends to try to operate smoothly, (unless you select TOGA).
Join Date: Jun 2001
Location: Surrounded by aluminum, and the great outdoors
Posts: 3,780
Likes: 0
Received 0 Likes
on
0 Posts
how to complicate something so simple...select the altitude, pull the damn knob..after it starts to climb, select any speed change you desire...
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes
on
0 Posts
Or more technically correct - wait until N1 reaches 95% as vllas posted #16
"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"
"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"
Thread Starter
Join Date: Mar 2006
Location: USA
Posts: 2,514
Likes: 0
Received 0 Likes
on
0 Posts
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?