If so, I guess, very sadly, you currently have a lot more free time to browse forums like this one. Hope any commercial pilots coming here will all be back in their cockpits when the current crisis eases.

Anyway, I fly the a320 in X-Plane only, but we like to have it as realistic as possible! May I therefore please ask... after takeoff I have usually engaged the AP before the flashing indicator to move to LVR CLB comes up on the instruments. When I move the throttles back to switch to LVR CLB, the aircraft's engines throttle back, sometimes quite alarmingly - I may go from, say 165kts to 140kts before they pick up again and the plane starts accelerating again. Is that a bug in the flight model, or does that actually happen? It does not happen in the a319 I also fly in XP11.

Advice I have been given is, on LVR CLB mode being indicated: 1. lower nose, 2. confirm positive yellow trend arrow pointing up, 3. Move AT to CL mode. Is that the procedure used in the real a320?

(With AP engaged though?).

I really don't understand why the engines should throttle back like that... the AoA/climb rate stays the same, there no indication at all that the plane is trying to compensate for 'pilot error'.. My T/O procedure is pretty much the same in the a319, and as I say, this does not occur there.

Many thanks.

Martin

Hi,

Generally I don't engage autopilot until after reducing thrust, and then the technique is to lower the nose first, then reduce thrust, otherwise the plane will lose speed.

I fly the a320/321 with IAE engines and have never witnessed a large speed decrease like that, unless an external factor such as wind is involved. The thrust should just move straight from TOGA or flex to climb thrust after moving the lever, and the aircraft pitch down to both climb and accelerate (assuming the thrust reduction and acceleration altitude are the same).

- If the autopilot is off, at thrust reduction altitude (when you get the LVR CLB prompt) the pitch bar on the flight director will "hop" down to a lower pitch. Lower the nose first, which will start the aircraft accelerating, then pull the thrust levers back to CLB.
- If the autopilot is on, just pull the thrust levers back to CLB. The autopilot will already have started to lower the pitch.

The aircraft should not decelerate as much as you say. Seems a bit weird. Maybe the model as you say.

What is your acceleration altitude? Same as thrust reduction altitude?

Re-reading your post, I find it weird that pitch and climb rate stay the same when the climb phase activates. (Note it is "pitch" and not "AoA"). Since you are decreasing thrust you have to lower pitch to maintain speed, and climb rate will also decrease due to lower thrust. I get the feeling the autopilot is trying to maintain too high a pitch rate after the climb phase activates. It should be referencing climb speed.

Modes should be as follows:
- Take off phase: MAN FLX xx (or MAN TOGA), SRS, RWY (sometimes), A/THR blue.
- At thrust reduction altitude, LVR CLB flashes. Once the lever has been pulled back to CL, MAN FLX xx (or MAN TOGA is replaced by THR CLB (or THR DCLBx). A/THR blue is replaced by A/THR white.
- At acceleration altitude, climb phase activates. SRS is replaced by CLB. Speed mode goes from takeoff speed reference to the climb speed target reference (managed or selected).

There is no rush to pull the thrust levers back to CLB. In some cases, e.g. more than mild turbulence or temperature inversions, you would want to keep the thrust at FLX/MCT or TOGA for a bit longer to ensure speed does not decay.

If your acceleration altitude is the same as the thrust reduction altitude, ensure the aircraft is accelerating before pulling the thrust levers back. If the acceleration altitude is higher, ensure the speed is stable.

Perhaps you could video the sequence and post on YouTube so we can see what is happening. Much easier to tell that way.

Nitpick: They're not throttles. They are thrust levers.

Martinlest, it should not matter whether the autopilot is engaged or not because the process is the same.

When you reach thrust reduction altitude (in the United States, it is normally 1,000 feet above field elevation), the FMA will annunciate LVR CLB and the flight directors will command a slight reduction in pitch to compensate for the reduction in thrust and still allow the aircraft to accelerate (NADP2 profile) or climb at V2 + 10 (NADP1 profile).

If the autopilot is engaged, it will reduce pitch to match the flight director. If the autopilot is not engaged, then you, as the pilot, reduce pitch to follow the flight director. The result is the same.

The key here is that you do not have to reduce thrust from TOGA or FLEX/MCT to CLB immediately just because the FMA begins to flash LVR CLB. At the company at which I work, it is flight operations policy to make sure the trend arrow is either neutral (acceptable) or indicating an acceleration (preferred) before selecting CLB.

With regard to your question, "Advice I have been given is, on LVR CLB mode being indicated: 1. lower nose, 2. confirm positive yellow trend arrow pointing up, 3. Move AT to CL mode. Is that the procedure used in the real a320?"

Yes, that is generally correct.

Correction to your terminology "Move AT to CL mode." I would say, "Move thrust levers to CLB."

Also, with regard to the loss of airspeed when you reduce thrust, my guess is that this is a function of your flight simulator software as I have never seen a loss of 25 knots in the actual aircraft.

e38

Such a big speed reduction is indeed not normal, the Autopilot should cope better. On the real aircraft I usually try to move the thrust levers slowly and smoothly to avoid scaring the passengers. This probably also helps to maintain the speed (possibly a technique you could try in your sim as well), however the AP should even be able to deal with a rapid thrust lever motion. I had a situation like you describe only twice so far, both on the same flight. We performed a flight (A321 IAE engines) to a destination that was only equipped with a CAT1 ILS in unexpectedly bad weather conditions (the ATIS weather was alright, but the actual conditions were much worse). During the first approach we didn't see the runway, my FO (who was Pilot flying) had already disconnected the AP and performed a manual missed approach. At thrust reduction altitude the FD bars were too high and the speed started to drop. I mentioned this to the FO and asked him to pitch below the FD bar to keep the speed under control. As the weather conditions seemed to be variable and the clouds were only scattered we tried an other approach, hoping to drop out of clouds before minimums. It was however the same situation and we performed an other go around, this time the approach and missed approach were flown with the AP on. The speed dropped again and eventually the AP was disengaged to avoid dropping below Vls, the pitch manually lowered and once the FD bars gave appropriate indications the AP was reengaged. Eventually we diverted to our alternate with better conditions and a CAT2 ILS. The modes on the FMA were correct during both approaches, I think that these problems were caused by the atmosphere not the aircraft (I did not monitor the temperature indication as we were busy, but I guess that there was a major temperature inversion sitting right at thrust reduction altitude which caused this loss of performance). Possibly the combination of low weight (at the end of the flight) with TOGA thrust also made the situation more difficult for the FD/AP.

Thank you very much for the replies - very useful. Sorry for my (Boeing-oriented?) terminology, BTW!!

I need to look at the replies further when I am flying the X-Plane a320. As you may be aware, the level of system realism/interaction in some of the X-Plane payware aircraft is phenomenal (or so it seems to me, as someone who has only flown single props real world), so I think all of this should be testable and/or achievable in the simulator.

When I've done that and have some feedback, I'll post again.

Thanks again,

Martin

One other thing... at what stage do you pilots push the ALT knob in order to engage CLB mode?

Martinlest wrote:

One other thing... at what stage do you pilots push the ALT knob in order to engage CLB mode?

We don't need to press the knob. CLB mode will activate automatically once the climb phase activates. Speed mode will then transition from SRS to CLB. It is important to differentiate between FM phases and autothrust modes.

The initial cleared altitude is set in the FCU before push. ALT will arm (blue). So you don't need to really do anything. The aircraft will follow the SID constraints until it captures the set altitude.

Once departures or whoever clears you to altitude or FL xxx, you set, cross-check, then press the knob. This gives you a managed climb. If you are in HDG mode, for exampl due to avoiding weather, you must pull the ALT knob and thus get open climb.

Right, thanks. I kind of asked the question wrongly, I meant when do you push the ALT knob to engage managed mode (rather than CLB mode). You answered that really anyway.

I think that that tallies with what happens.. (I get SPEED indicated on the PFD until I go to managed mode). As I say, I need to try all this out in the sim now...

Funny, the (ToLiss) a319 I also fly in X-Plane has none of these 'issues'.. but some of the problem in the a320 (with the speed fall off) is surely down to me, even so.

After a quick test, this seems much better. I do not engage the A/P now until after I move to THR CLB. Seems stable. I just have to remember to set managed mode before the dialed-in altitude is reached, or the AP switches to V/S and keeps climbing...

It shouldn’t keep climbing, or revert to V/S with the aural triple click. It should ALT* and the FDs should still capture the preselected altitude.

Seems like a bad flight model or Poorly written autopilot model.

Well that time it went to V/S... maybe a one-off.. can only conclude there's an error in the programming if it continues to do the same of course.

Did you change the altitude when it showed ALT* ? It would revert to V/S if the altitude capture mode is interrupted by setting a new altitude.

Simulator instructors will often intentionally time new altitude assignments with the engagement of ALT* to see if the students realize the aircraft reverted from managed or open climb to V/S. They’re checking if the pilots have good Flight Mode Annunciator awareness.

Martinlest wrote:

Right, thanks. I kind of asked the question wrongly, I meant when do you push the ALT knob to engage managed mode (rather than CLB mode). You answered that really anyway.

I think that that tallies with what happens.. (I get SPEED indicated on the PFD until I go to managed mode). As I say, I need to try all this out in the sim now...

Funny, the (ToLiss) a319 I also fly in X-Plane has none of these 'issues'.. but some of the problem in the a320 (with the speed fall off) is surely down to me, even so.

Martinlest wrote:

After a quick test, this seems much better. I do not engage the A/P now until after I move to THR CLB. Seems stable. I just have to remember to set managed mode before the dialed-in altitude is reached, or the AP switches to V/S and keeps climbing...

It should go to managed automatically unless you've set a preselected climb speed.

In the real world, if you got such a drastic drop off in speed during the climb, you'd press the ALT button (not the knob) or the V/S knob to immediately level off. Then you'd wait for the speed to come back up to the speed target before pressing or pulling the ALT knob.

As mentioned, at acceleration altitude you should get THR CLB, CLB, A/THR on the FMA with ALT in blue (meaning altitude capture armed). The speed mode is THR CLB, which holds the managed or selected climb speed by maintaining constant thrust and varying climb rate with the elevator and stabiliser. The vertical mode is CLB with ALT armed.

What is the altitude set in the FCU window? Should be lowest of the cleared altitude or the first max altitude constraint on the SID. If it is lower than acceleration altitude you could get wonky behaviour.

What is showing on the PERF CLB page on the MDCU? Once you reach the acceleration altitude and go from SRS to CLB, autothrust will engage and your speed will be the managed speed unless you've preselected a climb speed. You can see here that a speed has been preselected since the number "275" is large and ACT MODE says "SELECTED".

It sounds like you need to report a bug to whoever made this addon if it is an addon aircraft. I used the Aerosoft product on P3D and it isn’t perfect but the only issue it has at this point of the flight is that the CFM engines don’t reduce fast enough; otherwise, it never loses that kind of speed.

Right.. thanks again - a bit belatedly - for the replies. Will post back a screenshot when I can, but meanwhile, my changed TO procedures (as above) have reduced this issue.