A320 NEO Open Climb Thrust Logic

[CW247]

To my amazement yesterday, I dialed in a new altitude into the FCU window and pulled for Open Climb. 3 seconds later I selected a reduced speed (20 KTS less). The engines powered back to target the speed before climbing. Has something changed with the logic?

[BRAKES HOT]

Leaps? Strange logic I agree - I've seen this also. They always seem a bit lazy compared to the CEO. Need to wait until they're properly established at climb thrust before pulling speed to avoid them rolling back, you probably just caught them before this.

[Amadis of Gaul]

I've seen that both on 1100Gs and on IAEs.

[CW247]

Yes LEAPs

[champair79]

This happens on our IAEs too. The solution is to either wait until climb thrust is set or wind the speed up briefly to force the engines to accelerate rapidly to ‘lock in’ the climb thrust before reducing the speed again to increase the ROC.

Idiotic logic imo. Surely if the FMA is displayed, that’s what it should be doing!

[vilas]

Originally Posted by CW247

To my amazement yesterday, I dialed in a new altitude into the FCU window and pulled for Open Climb. 3 seconds later I selected a reduced speed (20 KTS less). The engines powered back to target the speed before climbing. Has something changed with the logic?

Twenty kts is a big reduction. Let's consider how else the system can do this. Once the system is locked in OP CLB the speed is controlled by pitching only. It is limited by maximum attitude so it will take longer to decelerate. More rapid speed reduction is achieved by throttling back and then resuming climb. When you dialled lower speed what was the N1?

[vilas]

It has nothing to do with Neo it should be same on CEO. I had posted this before open climb is initiated through speed VS mode. It was disclosed by Airbus in Sochi investigation. Below is from the report:

[CW247]

To make it clear, I set the new FL, pulled for OPEN CLB, read the FMA, the N1 was on it's way to reaching maximum CLB thrust. At this stage I dialed in the new speed, the N1 fell backwards to chase the speed, not the pitch!

15 years of operating this aircraft, this is not the logic I have experienced before. I've flown MSN 300 all the way to 7000. In fact, I flew LEAP based NEOs for another company, and it didn't happen with those either. I'm now flying LEAP based NEOs that are under 1 year old and see this happening. My very experienced colleague said he too has never seen this behaviour before on A330s, A340s or A350s.

[CW247]

I found the older thread on this: https://www.pprune.org/archive/index.php/t-625919.html

Villas, I can see your contribution but don't agree with your reason that Airbus does this to smooth things out. We can and DO do that ourselves by adjusting the speed. I reckon this is a glitch that has something to do with me being in HDG mode. Just spoke to another colleague flying the same aircraft today, he didn't experience anything of the sort.
On the Boeing, we have FLCH mode. Same concept. Works as anticipated. Full climb thrust, Idle to descend. No chasing the speed.

[PENKO]

Vilas, many thanks for the reference! I always wondered what ‘crazy’ logic the Airbus was following. I have seen this behavior on both 319’s and 320’s, CFM CEO’s and LEAP NEO’s. It typically happens when you have been flying on a higher selected speed when leveled off and pushed for managed speed as soon as you get further climb. The engines will almost go to idle initially.

The opposite is also true, if you want a faster thrust response after selecting CLB, select a higher speed.

[vilas]

Originally Posted by CW247

I found the older thread on this: https://www.pprune.org/archive/index.php/t-625919.html

Villas, I can see your contribution but don't agree with your reason that Airbus does this to smooth things out. We can and DO do that ourselves by adjusting the speed. I reckon this is a glitch that has something to do with me being in HDG mode. Just spoke to another colleague flying the same aircraft today, he didn't experience anything of the sort.
On the Boeing, we have FLCH mode. Same concept. Works as anticipated. Full climb thrust, Idle to descend. No chasing the speed.

This is the way the system is designed and works. However as I said if thrust is locked in THR CLB only way for the mode reduce speed is by pitching and there's a limit on pitch up attitude also it only pitches at 1.1 g. It has nothing to do with heading mode. You will only experience this if you reduce speed and the N1 is less than the required to switch to real OP CLB mode. Next time try after thrust is set.

[321XLR]

Originally Posted by CW247

To make it clear, I set the new FL, pulled for OPEN CLB, read the FMA, the N1 was on it's way to reaching maximum CLB thrust. At this stage I dialed in the new speed, the N1 fell backwards to chase the speed, not the pitch!

15 years of operating this aircraft, this is not the logic I have experienced before. I've flown MSN 300 all the way to 7000. In fact, I flew LEAP based NEOs for another company, and it didn't happen with those either. I'm now flying LEAP based NEOs that are under 1 year old and see this happening. My very experienced colleague said he too has never seen this behaviour before on A330s, A340s or A350s.

My understanding is once Speed is selected (pulled), the speed value set becomes the #1 priority over everything else. Open Climb will continue (ignoring constraints) but the priority is the speed. "How" it does that, pitch/thrust etc, how much OF pitch and thrust, etc, may indeed be a software thing.

[vilas]

Originally Posted by 321XLR

My understanding is once Speed is selected (pulled), the speed value set becomes the #1 priority over everything else. Open Climb will continue (ignoring constraints) but the priority is the speed. "How" it does that, pitch/thrust etc, how much OF pitch and thrust, etc, may indeed be a software thing.

With OP CLB on FMA once thrust goes past 95%N1 all speed changes (decrease or increase) will be by pitch change. Thrust will remain locked at THR CLB.

[CW247]

We clearly live in parallel universes here guys!

And what happens vilas, if max climb thrust is capped at 85%, and therefore N1 never reaches that value? (95% is very high)

[Scagrams]

Originally Posted by CW247

We clearly live in parallel universes here guys!

And what happens vilas, if max climb thrust is capped at 85%, and therefore N1 never reaches that value? (95% is very high)

It is 95% of the MAX CLB, ie in your example, 95% of 85% thus around 81% actual N1

[vilas]

Originally Posted by CW247

We clearly live in parallel universes here guys!

And what happens vilas, if max climb thrust is capped at 85%, and therefore N1 never reaches that value? (95% is very high)

Scagrams is right. Perhaps it is a translation from Russian. What I quoted wasn't my guess work. It was data provided by Airbus in a fatal accident inquiry. So there's no question of its authenticity. In simpler language it means initiation of OP CLB is through SPEED, VS mode and real characteristic of OP CLB starts from 95% of CLB N1 i.e. when thrust almost reaches CLB. Design philosophy. In a go around irrespective of lateral mode TRK/HDG or Nav the SRS changes only to OP CLB. Why? Design philosophy.

[321XLR]

Originally Posted by vilas

With OP CLB on FMA once thrust goes past 95%N1 all speed changes (decrease or increase) will be by pitch change. Thrust will remain locked at THR CLB.

excellent thank you

[CW247]

OK thanks all for your input. So it appears that because the LEAPs are so sluggish to power up in the first place, we are seeing this outcome

[vilas]

Originally Posted by CW247

OK thanks all for your input. So it appears that because the LEAPs are so sluggish to power up in the first place, we are seeing this outcome

Now that you know the design of the mode one could prioritise between climb and speed reduction. If climb has priority then wait till climb N1 is set then reduce speed that will climb also pitch it up to reduce speed. Want to reduce speed then do it simultaneously with pulling climb.

[CW247]

That's very helpful. I'm on a mission now to discover how many pilots know this. It's not in the FCTM.