Question for A-320 drivers
 

Many a times I have seen pilots pulling speed or vertical speed to get to the cleared altitude faster during the climb out. My own understanding is that one should let the speed stay "managed' as this would be the most efficient way of getting up there. At times there is a tail wind component and pilots feel that if they get up there faster, they will benefit more.

Hope someone will clear this up.

Many possible reasons. Penetrating through the clouds quicker ( Pax. comfort ), maybe the flight is late so the PF wishes to catch up some time.

Managed climb and speed is set by FMGS according to many factors, and although it is the best profile for normal operation, it is not always the most practical setting.

Hope this helps, and am sure you will get more answers

@Davidils201
Thanks. May I clarify that the weather is not a factor and can you elaborate as to how can you save time this way because although you have climbed faster but now have a greater distance to cover.

Dutch & German ATC often give you min rates of climb/descent to maintain so that's another reason.

I have heard a rumour that certain unscrupulous individuals have also been known to operate in V/S mode in climb or descent because they want to sneak above 250 kt below 10,000 ft, without getting hassle from ATC.

Because the speed ATC "see" is the one that's selected, and because V/S mode has priority over selected speed mode, if you select 250 kts on the speed but also select a suitable rate of climb on the V/S, and manually select climb thrust, it will accelerate below 10,000', still with 250 kt selected.

It's even easier in descent, because you don't have to manually set the thrust, as long as you have selected a decent ROD ( >2000 FPM), it will maintain the high speed right up to alt capture and once again all that ATC see, apparently, is the selected 250.

Sounds kind of b*****ks to me, but that's the way it's been explained to me by a couple of guys I've flown with anyway.

Thats a bit complicated! Out of Heathrow ATC will often clear you to a higher altitude sooner if they know you can be above the holding stacks before you reach them, otherwise you get a long track at 6000 ft until you've passed beneath them. I know certain airfields in Germany have long SIDs in order to ensure you reach a certain altitude before the FIR boundary. The sooner you get the altitude the sooner they can clear you on a much shorter direct routing off the SID.

This depends on what you mean by "most efficient", with the correct CI in it will be the most economical, but it will take longer to get to alt. than at lower speeds (down to GD) and there can be all sorts of reasons you might want to do that.:hmm:

At LukeSkyTodler:
What do you mean, the speed the ATC can "see" is the selected speed.
Would they not read out the GS of the aircraft?

Hence they ask what the indicated speed is, or mach number?
Would a mode s transponder show the selected speed?

Many reasons to use V/S though, one of them to slow down your V/S when approaching your target altitude to avoid TA's or RA's to other traffic around.
Rgds

Luke,

I don t think they can see selected speed at all. Only IAS/VS/HDG and selected altitude. Any controllers care to comment?

Certainly on the bus, Open Climb, Open descent, etc are very slow to react via autothrust. Using VS can get you going up or down sooner.

Something you need to watch out for, if the pilot quickly selects a lower speed... If you are extremely light...the aircraft will rocket up, you will get an alt * and overshoot the altitude by 3-400 feet. If you are extemely heavy and try to zoom the aircraft you have the possibility of having a tail slide...to get out of it you need to disconnect the auto pilot and push it over.

Back to the video arcade Iceman

To get there faster, you simply select a lower speed (CLB or OPEN CLB). Indeed Airbus clearly states that use of VS mode is not recommended since it can confuse the FMGS (selecting an unattainable IAS for a given VS can confuse the FMGS).

The only arguments I can think of are to use VS to avoid large pitch changes.

VS can be useful on the A320 series when you are heavy, the wind is unstable, and you are above FL300. In these conditions the aircraft VS can rapidly oscillate between (for example) 300fpm to 1500fpm in order to maintain the selected IAS as the wind changes. Small changes in IAS trend = large change in pitch/vertical speed under these conditons. This can be avoided by selecting M0.80 (ie power on), VS+1000, and closely monitoring your IAS as it varies.

There is also an argument to use VS during a very turbulent descent. OPEN DES can again cause large rapid pitch changes, and DES can cause VS-1000 and power to be added if you temporarily go below the profile (you probably want to get under the profile/wx in these conditions). So if you wind the speed back to green dot and select VS-2500 (for example... depends on altitude etc), you should keep the power off and a fairly constant descent rate even as the wind changes. Again, you must monitor IAS closely.

To claim, ATC can see anything you select on the flight control panel, be it Speed, rateofclimb or selected Altitude, is complete nonsense...

They see the following: Your Groundspeed as calculated by the Radar (it is not transmitted), your present Altitude (transmitted by the transponder), your Squawk (usually computerchanged to your callsign), and on mode S they actually do recieve the call sign.

Nothing selected ever gets transmitted, and pilots trying to fly faster than 250 below 100 by selecting V/S don't have the slightest clue.
If I want to fly faster, I just ask, or see if I am in class C airspace, where no speed limit apllies...

Nic

Admiral, better watch out.
A controller can tell us more, but I know that depending on software installed, the comtrollers can see SELECTED alt, hdg and speed.
This is certainly true for the London TMA and parts in Germany.

Once, flying out of Luton, we were cleared to to climb to FL120.
FL120 was selected and read back, however the PnF had doubts and subsequently asked the controller to confirm 'you want us to climb to 12- or 130?'

Response from the controller: The level you've got SELECTED is correct, climb FL120.
:ok:

==

Arrowhead, what exactly do you mean by 'setting an unattainable IAS can confuse the FMGS'. I am far from being an expert on the subject, but I have never heared of this.

So what kind of confusion are we talking about???

If you change the speed, you are effectively changing your cost index, so in that respect, managed speed is more efficient, however, the A320 is no rocket ship and if you are heavy it will occasionally stop climbing at all in managed speed, 500 FPM is the minimum climb rate, using one of the two methods mentioned will solve the problem.

Be Careful!!!!!
 

Using V/S is OK...but, you have to watch your airspeed. You can't set Vertical Speed and go back to reading your newspaper or magazine. You could have unacceptable airspeed excursions.

With regard to Managed Speed and the uneven climb rates (sometimes drops to Zero for a moment or two), Airbus says that's OK. It's still the most efficient (based on your selected Cost Index).

Personally, I like to use Managed Speed when all things are wonderful. But, throw in turbulence, or ATC requests/requirements, etc., etc....I may have to resort to V/S.

Another method is to Select Speed/Select Mach to something a bit slower (not too slow), to give you a short-lived boost in the pants. This works...depending on your immediate requirements.

With regard to the 500 FPM minimum...it is not a minimum climb rate...You can climb at only 50 FPM, if that amuses you. It's just that anything less than 500 FPM requires notification to ATC. In the case of momentary drops in climb rates in the Managed Speed profile, ATC need not be notified, unless the drop is more than 'momentary'. This is up to your judgement...what ATC calls to make..., captain.

Hope this helps....

PantLoad

True but I didn't think I needed to point out the obvious. There is a technique that I use which is a combination of the two, selected speed at Vmax, V/S at a rate within reason, no bobbing up and down, engines don't spool down by reaching managed speed.

A big thanks to all for taking time out and replying to my query

Flying a managed climb, the aircraft will match all speed/ Alt constraint programmed in the MCDU. The plane will juggle speed and ROC to match these constrains. If you pull open clb, the plane gives you the best ROC and ignores all constraints.

If this was true, managed speed would always remain the same given the same weight no matter what the CI selected, we know this is not true, what led you to this conclusion? :confused:

To be honest the Q I had asked was " if the weather/ ATC /constraints is not an issue is it better to let the speed stay managed during a climb out or as I have seen some pilots select a lower speed / higher V/S to get to the cleared altitude faster. Would this result in any fuel saving, on say a 2-3 hour flight.

Not a self appointed expert but I would assume if your airline was that worried about it, each flight segment will have an assigned cost index to follow, playing with selected speed and V/S is changing the CI, having said that, pilots seem to enjoy manipulating the climb and descent to suit their needs, for instance, our base is close to an FIR boundary, we try to help the controllers by reaching our cruise level prior to that boundary, relieving the need for coordination with the next region. Another way to answer your question is by simply inputing your CFP data for that length of flight, now, whatever CI you used, now change it to "0", now compare the burn on the INIT page for your answer. Remember, operating cost is much more complicated than saving fuel.

Dream Land. For a given set of parameters CI, weight, temp............etc. Open climb will give you best ROC







What do I know. I only work here:ok:

Maybe your definition for Vy is different from mine, please explain what CI has to do with best rate of climb.: :eek:

Only with putting CI of zero during climb, this will give you the best rate of climb speed Vy.

loc 22550 is right. Let's simplify it all:
Open Clb: Give me climb thrust and maintain the speed (selected or managed) with the elevators.
Clb: As above but please obey any constraints.
Exp Clb: As for 'Open Clb' but fly Grn Dot speed. (ie max gradient).
CI 0 gives max rate of climb
Cheers
mcdhu

Thank you mcdu and loc 22550. :D

I think you lot need to go back into the books!...

you don't give me much confidence!...

are you really A320 drivers?

well put mcdhu.

dream land three posts back you asked what CI 0 has to do with Vy. what's with all the applause. Make up your mind.

Hiya sharpshooter.

"Pulling" speed may be the quickest way to get to a cleared FL but it is not neccesarily the most efficient. The 'bus (specially the 321) has a tendency to lag a little at the higher FL. Ie ROC = <400fpm, if one is particularly heavy. One course of action is to go selected speed and reduce speed by 5 kts or so, Causing a kind of mini zoom climb, this is quite useful if you only have maybe 2000ft to go.
My company sops explicitly forbid use of VS at all above a certain flight level as the Aircraft will disregard speed to get its desired ROC, possibly leading to alpha prot etc.....
With regards to your post, leaving the aircraft in managed speed for the entire duration of flight is more efficient, however it is very rare that one will be able to do this as ATC constraints, etc exist on nearly every route I have ever flown!:)
Tacho

Tacho

Shouldn't get to Alpha Prot. If a too high V/S is selected, the speed reduces, but when it gets to VLS the Autopilot ignores the V/S command and will maintain VLS. The FMA will still show the demanded V/S.


This though does mean that you are climbing to altitude with the speed way back on the drag curve. Not a good place to be - see the Pinnacle Airlines CRJ stall, double engine failure crash as a perfect example

Be careful out there!

T'bug :ok:

taperlok, your original partially incorrect statement that indicated that when OPEN CLB was selected, you get Vy, I challenged that statement since I knew that every time you change CI, managed speed will change, do you get it now?
mcdu and loc22550 corrected your statement, not sure if you understand that though. :hmm:

Yes, this is called a reversion, no chance of a tail slide either. :}

oops, wrong term, doh! right sentiment. thanks! :ok: Basic point I was trying to make was that it will neglect the speed for the sake of ROC.

cheers.
Tacho

in reply to the original post
 

situation: normal flt/no wx/no atc input/no reason really, to select v/s or lower speed.
except the pilots perception that by doing so one would reach CRZ level faster and thereby enjoy the tail wind for a longer period of time.
lets assume that you are able to select a higher v/s or lower speed at the earliest,say 5000'. assume CRZ LVL 390. normal climb time average (without touching FCU) ~ 20min.
In flying selected speed or v/s, say we get there in 18 min.(IMHO Pffsss)
you end up flying at least 1 extra min of CRZ and have in net total managed to completely muck up the airspace that you climbed through.and spend another minute longer in CLB thrust to attain CRZ speed
If your CRZ LVL is lower and if you only do it from FL100 then, we are dealing in seconds.
these are entirely my take on the situation.
your call

Thank you gentlemen, your inputs have been most helpful. Cheers

Seen the tail slide 2x, once when I new on the aircraft and the othe pilot was showing his technique to go up quickly, and once while in the jump seat giving a line check...both were on a heavy aircraft ..definitly not in the video arcarde. Also, departure out of Gatwick...knows what altitude you have set in the FCU

Mate, a tail slide is what you do in your car, this is a pilot forum. :}

The aircraft stopped climbing, (did not stall), and was losing altitude with the nose high. Sorry that I referred to an improper term...probably the difference between bonnet and hood. :)

Roger, understood! :ok:

Iceman,

I've never heard of the FCU selections being transmitted to ATC (presumably by the transponder). Where did you get this information? Indeed perhaps it IS transmitted but I cannot find any reference to it in the manuals.

Anyone from the engineering side care to comment? Could this be another of Airbus' "little foible" that they choose not to tell us mere drivers about?