A330 A/THR

[Contact Approach]

Coming across the pond (westbound, as PAX) I noticed the A/THR system really struggling? to maintain a constant (or at least responsive) power setting when dealing with the winds aloft. They'd go from idle to climb, back to idle and so on (My limited observation, anyways). Obviously it's chasing the IAS, but why such massive fluctuations in power? Perhaps the wind is stronger than I'm used to in Europe? Great airplane otherwise!

[Contact Approach]

any 330 drivers care to add?

[SloppyJoe]

It is actually very good usually. During cruise when the autothrust is on and in MACH mode it is what is called a soft mode (I think that's the terminology) , it makes smaller changes in thrust and the deviations in speed are sometimes realatively large whilst the thrust progressively increases or decreases smoothly to counter the trend. The further away from the selected or managed bug the more aggressively it tries to catch it but it still attempts to do this smoothly.

If it is having trouble staying away from green dot or MMO I have come across a few guys who will select a speed (push the button to take it out of Mach and into Speed mode). The result of this is the A/THR is now very much tighter. Any deviation from this now selected SPEED results in an almost instantaneous correction from the trust to reverse the trend back to the selected value. It does not sound nice in the cabin although it is actually maintaining the target speed with much better accuracy. If you hear it doing this it should not concern you, it is in fact a sign the guys/girls are awake and very closely monitoring the situation.

If you heard rather spaced changes from near idle to climb then it is likely they had it in the soft mode with Mach selected (managed or selected but in Mach), this is just how it deals with large fluctuating winds as the speed can get quite far from the target value before it really goes after it.

If it was very quick with power on and then off, multiple times a minute then it was probably as I stated about them changing from MACH to SPEED.

Without going into the books I can't go into much more detail although am sure someone with far better knowledge than me will be along shortly.

[Uplinker]

Yeah, kind of.

What actually happens is that in managed speed, (speed button PUSHED = magenta speed bug), the aircraft will allow altitude variations of +/- 200' in order to avoid 'hosing' the engine's thrust up and down to maintain speed. This is the so-called soft altitude hold, which saves fuel, and gives the passengers and crew a relaxed cruise.

However, when crossing the ocean, one is usually cleared to do so at a specific mach number, and one therefore selects the cleared mach number for crossing, (speed button pulled = blue speed bug). Selecting the cruise speed/mach cancels the soft alt mode, and therefore causes the engines to 'hose'up and down a lot more keep to the selected speed/mach.

[ahramin]

Was this for the entire crossing, or a short period of time? Turbulence?

[Uplinker]

Entire duration of the clearance, which is usually the whole crossing.

In turbulence one generally slows down to keep the speed halfway between green dot and Vmax.

[Contact Approach]

Thanks guys, I am a bus driver, just very new and fly the much smaller kind.
I hadn't come across this before, perhaps because i'm not sat in the cabin listening!
I had presumed it was as you said... it was a fairly bumpy crossing so I'm guessing it happened more as selected speed would have been selected during such times.

[A-3TWENTY]

I Think the FG of this airplane is crapy.

The A/THR soft mode allows a variation of +- 3 kts , when in ALT CRZ and above M.65.

The point is , sometimes you are already 10kts above or below your target when the A/THR slooooooly starts to adjust, That`s why pilots have to intervene , selecting mach and sometimes changing to IAS.

By the way , the same poor behavior hapens during descent specially in the 300 series. Speed goes sometimes 10 kts above the bracket and takes times to reduce by itself.

Not to mention the calculation of the descent profile. If we are high on profile , it shows the intercepting point , and then as we get closer it moves ahead over and over again; it was suposed to be at 250kts at Fl 100 and it does not reduce , or starts reducing well before and all of sudden you find yourself at 250 kts at level 130 , etc....

My company planes are equiped with Thales...

The A320 is a loooottttt better than the A330.

[SloppyJoe]

Oh well did not want to get the books out but as someone mentioned what I was saying was incorrect and then corrected it with a common misconception I thought I better had.

Uplinker.

In my explanation when I was mentioning changing from MACH/SPEED I was not talking about managed or selected. Like I stated, the little black button that flips from MACH/SPEED.

Selecting a MACH number does not take it out of soft mode, you have to select a SPEED. It is also nothing to do with altitude variations.

From the FCOM:

When the aircraft is in ALT CRZ mode with the autopilot engaged, autothrust engaged in MACH
mode, and is within a  3 kt range of the target speed, the autothrust soft mode engages. This
mode reduces the thrust variation in cruise specifically in light turbulence. The autothrust soft
mode disengages when the speed deviation from the target becomes too large or the target is
modified ; autothrust transition from soft to basic mode may lead to transient thrust variation. This
mode is inhibited with speedbrakes extended, or with engine out or when Mach target is below
0.65.

What actually happens is that in managed speed, (speed button PUSHED = magenta speed bug), the aircraft will allow altitude variations of +/- 200' in order to avoid 'hosing' the engine's thrust up and down to maintain speed. This is the so-called soft altitude hold

It actually does not do this. The AUTOPILOT maintains the level accurately and there is no such thing as soft altitude hold. After looking in the FCOM it turns out it is called A/THR soft mode. If a +/- 200ft variation was allowed do you think this aircraft would be certified to fly in RVSM? What if its altimeter was at the limit of the allowed error and it was meeting another A330 coming the other way with its autopilot allowing 200ft in the other direction with its altimeter out by the limit the other way. How much space would this leave between the two A330s?

[nitpicker330]

Yep +/- 200' is wrong.
The A330 isn't as good in turbulence as the 777 or the 744. It's speed Un-stable!!
Don't start me on climb or descent speed control!!

Generally the ride in turb is crap. It wallows all over the place rocking wings and the Thrust going up and down to try and keep the speed......:{

[C_Star]

The A320 has a soft ALT mode in cruise, allowing for 50' altitude variations - is the -330 different in that respect?

[Contact Approach]

The 320 soft mode doesn't have the engines wailing all over the place, though.
Many thanks for the answers guys.

[SloppyJoe]

The A320 has a soft ALT mode in cruise, allowing for 50' altitude variations - is the -330 different in that respect?

Have looked and see no mention of this and never heard it spoken of during training. I am almost certain that the 330/340 does not have this soft alt mode. Also when flying I have never seen it deviating from the selected ALT (CRZ) without correcting to regain it, even by 10ft on the side the active AP is on.

[MCDU2]

Soft N1 or EPR mode is mentoned in my fcoms. Actually in quite a few places such as the sop section as well as system related fms section. Airbus seem to call it slightly different names in different sections. Also called a/thr soft mode to. Hence why if you are given a lower than planned cruise level you need to manually insert this into the PROG page to benefit from it.

[DozyWannabe]

The A330 isn't as good in turbulence as the 777 or the 744. It's speed Un-stable!!

The systems are designed to work differently and can't be compared in the same manner. The T7 and B744 trim for speed stability and the automatics work around that. The A330's trim system responds constantly to changes while trying to maintain the flightpath.

It ain't worse, just different.

[nitpicker330]

Sorry but IT IS WORSE. I don't care how the white magic works in the background the END RESULT is a sloppy bumpy jerky rolling crappy ride in even light turb.

[DozyWannabe]

I defer to your experience, but as an SLF who transits the Atlantic several times a year, I've never noticed a worse ride in turbulence on Brand A jets compared to Brand B.

(And let's not beat about the bush - you *really* don't like the A330 based on your posts...)

[Capn Bloggs]

The systems are designed to work differently
And obviously worse. Dozy, the great Airbus apologist...

And let's not beat about the bush - you *really* don't like the A330 based on your posts...)
Probably because he has flown both extensively and can compare them? Why can't some people accept that one product is worse than another?

[DozyWannabe]

And obviously worse. Dozy, the great Airbus apologist...

You clearly must have missed me requesting Boeing be given the benefit of the doubt regarding the B787 battery issues a while back. I am, as always, platform-agnostic.

Probably because he has flown both extensively and can compare them? Why can't some people accept that one product is worse than another?

I'll accept such a judgement on the basis of objective analysis, but please understand that it's hard to treat an analysis as objective when the source has been slating the platform consistently...

(For the same reason as I wouldn't expect anyone to take my views on Apple [whom I loathe as a company and as a platform] in the same way...)

[nitpicker330]

Hey the Airbus isn't too bad, I quite like a lot of features it has---

Tray table
More comfortable seats where you can actually cross your legs!!
Quieter
Less drafty in the cockpit ( although the temp control is fascinating !! )
Better Sec Flt plan setup ( rest of the FM is way too complicated and has stuff all over the place )

Plus best of all It files me home and gives me an Aussie basing, what's not to like :ok:

However I stand by my other negative comments and yes I have considerable experience on both types.:)

[Flo121142]

If we are high on profile , it shows the intercepting point , and then as we get closer it moves ahead over and over again;
I don't know how this is calculated on the A330 (rated on A320), but on the A320 this is the way the system is designed. If you are high on profile the intercept point is valid for a descend with half speedbrakes. So without speed brakes the intercept point will move forward. Not sure if its the same on the A330 but from your description it seems to be...

[Axel-Flo]

WRT Uplinkers reply earlier,
and just as a question, would the selection of "Constant Mach" in the FMGC not be more normal on a NAT Track rather than pulling a Selected one? Also WRT the original posters comment on the thrust maybe hunting from idle to climb does the cost index make any difference to this....?

[4468]

Anyone thinking 777 is speed stable in turbulence (even light turbulence) has probably never flown it!:rolleyes:

Airbus is fine. Each product has it's pros and cons, though I accept one manufacturer's product is much more like the basic machine people would have trained on, and is therefore likely to be more intuitive in the early days. After a while Airbus becomes moderately intuitive too, though some features will always present a challenge. Normally connected with tactile/visual monitoring of flight control/auto thrust inputs!

Like I said. Both products are fine.

[nitpicker330]

777 isn't perfect by any stretch of the imagination but it is better than the 330.

744, now there's a good machine, rides bumps very nicely:ok:

[hikoushi]

One technique that some people do that I've seen cause big power fluctuations
is a very gradual VS climb while maneuvering in a block altitude. Like, VS +200 FPM or such. Usually imperceptibly smoothe, but if the winds are variable through that altitude block, the power can get pretty active. This would certainly not explain feeling surges like that for most of the flight, though.