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The cruise speed drops suddenly


XCSWxcsw

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I just flew from EPWA to ZBAA. During the cruise, the speed suddenly dropped from the managed M0.82 to 119 knots. I am pretty sure I did not perform any APPR phase or speed restrictions and something else. It started from the climbing phase.

I can't solve this problem, so I temporarily selected speed M0.82 to fly. As long as I change back to manage mode, it will jump back to 119 knots. 

 

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P3Dv5 HF2

newest A330

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  • Deputy Sheriffs

Hello XCSWxcsw,

First of all it looks like not all your screenshots have loaded correctly. At least I can see just one screenshot that loaded up while 4 others are just corrupted "unknown.png". Could you try to upload them again maybe?

Secondly, this issue is something that we know exists but we are not able to reproduce this issue or simply have no idea where to look to fix this right now. Are you able to recreate this issue on this flight consistently? What route did you fly? What CI did you use? How long into the flight this issue happened (any location like x nm from waypoint y)? Did you make any changes in the FMGS when this happened (change in cruise FL or CI for example)?

If you are able to recreate it, could you try to send us the log files (Preferably zip the whole Data folder inside the Aerosoft A330 folder and post it here) or try to catch the moment it happens on video.

This would be really helpful since we are currently completely relying on customer information with this issue to get better understanding what could be causing this. The testing team is totally unable to recreate it consistently, so we have no idea what is causing this or where to even look from.

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This happens to me as well...a lot. It could happen on climb and randomly at cruise. Happens so much that I go into 'selected' mode as soon as I hit cruise so it doesn't happen randomly when I'm flying. Also happens in all fleet types too. I will try pinpointing the exact time and send you guys the info to help fix this. 

 

Edit: Happens in A319 through the A321 models. Haven't yet seen it in the 330. Didn't mean to hijack the thread.

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  • Deputy Sheriffs
5 hours ago, syndola said:

This happens to me as well...a lot. It could happen on climb and randomly at cruise. Happens so much that I go into 'selected' mode as soon as I hit cruise so it doesn't happen randomly when I'm flying. Also happens in all fleet types too. I will try pinpointing the exact time and send you guys the info to help fix this. 

 

Edit: Happens in A319 through the A321 models. Haven't yet seen it in the 330. Didn't mean to hijack the thread.

Anbd which exact version od P3D and the Buses are you using?

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P3d v4.5.13.32097

 

Buses at 1.2.3.0

 

Had to open the updater to see the version, however I noticed a newer version was released in April. My apologies. I considered since the updater didn't allow me to update, I had the latest, however I just now saw Mathijs' note and will update. Will create a thread if still experiencing the same issue.

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On 7/30/2020 at 12:26 PM, Secondator said:

Hello XCSWxcsw,

First of all it looks like not all your screenshots have loaded correctly. At least I can see just one screenshot that loaded up while 4 others are just corrupted "unknown.png". Could you try to upload them again maybe?

Secondly, this issue is something that we know exists but we are not able to reproduce this issue or simply have no idea where to look to fix this right now. Are you able to recreate this issue on this flight consistently? What route did you fly? What CI did you use? How long into the flight this issue happened (any location like x nm from waypoint y)? Did you make any changes in the FMGS when this happened (change in cruise FL or CI for example)?

If you are able to recreate it, could you try to send us the log files (Preferably zip the whole Data folder inside the Aerosoft A330 folder and post it here) or try to catch the moment it happens on video.

This would be really helpful since we are currently completely relying on customer information with this issue to get better understanding what could be causing this. The testing team is totally unable to recreate it consistently, so we have no idea what is causing this or where to even look from.

Hi,

I can't find that screenshot. For your questions, Not only in that flight, it happens 3 times. CI is 80, about full flight, i didn't change any data from MCDU.  

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  • Deputy Sheriffs

Is there any common denominator on those flights where it happened? Did it happen on the same route? Around the same place? Same arrival? Or was it just completely random on different flights with different routes?

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13 minutes ago, Secondator said:

Is there any common denominator on those flights where it happened? Did it happen on the same route? Around the same place? Same arrival? Or was it just completely random on different flights with different routes?

nothing in common.completely random

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  • 4 weeks later...

Hello, I have just had this happen to me, also.  I had to step away, but I'm pretty sure when it switched to managed cruise mode, it is idling the thrust.  Had to set the speed myself for the remainder of the flight.  Climb was good, but it also did the same thing when I tested managed mode during descent phase.  I am on P3dv4.5.14.34698, with AS A320-321 Pro v1.3.1.1.  This was the A320 regular CFM model.  My route was KATL to KSAT, crz alt of 36000 ft, and a CI of 23.  I also did not make any changes to the MCDU during flight.  I don't have any screenshots, as I was trying to save my aircraft, but like I stated, at Cruise Phase with managed mode selected, the aircraft idled the throttles until Alpha Floor, but it did not seem to try to recover on its own, I had to take control myself.  It was already in TOGA LK when I noticed the issue.

Data.zip

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  • Deputy Sheriffs

Hello iforrage,

I can see the speed drop on your logs at around 12:00:00. Unfortunately we are unable to currently determine the cause of this issue still. Do you the route available that you flew. Did you have the arrival runway, STAR and possible transition selected? How about PERF APPR filled? We would need to find some common denominator on these speed issues that we could track down to find the root cause why this is happening.

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On 9/3/2020 at 3:25 AM, Secondator said:

Hello iforrage,

I can see the speed drop on your logs at around 12:00:00. Unfortunately we are unable to currently determine the cause of this issue still. Do you the route available that you flew. Did you have the arrival runway, STAR and possible transition selected? How about PERF APPR filled? We would need to find some common denominator on these speed issues that we could track down to find the root cause why this is happening.

 

Hi,

The route for this flight was:  KATL/27R KAJIN2 STNGA DCT WINAP Q40 AEX DCT IAH BRAUN3 KSAT (ILS RWY 13R No VIA).  All fields were filled in the MCDU.  This happened at cruise, but was continuing through descent phase.

 

I am doing a flight currently, taking screenshots, and have flight recorder on as well.  The weird thing is, it did happen this time, BUT, since I was paying attention, I was still in climb phase, and it commanded 155 KIAS about 3000 feet before cruise level was reached.  I took it out of managed speed, and manually commanded .78 mach.  I then switched back to managed mode, and it has been fine since.  Reached cruise phase, and still set at .78 mach managed.  Nothing on the previous flight worked as far as disabling/enabling managed mode.  Every time I tried to command manage mode, it would want to reduce speed.  Maybe because I caught it this time before cruise phase was active?  Dunno.  It's puzzling to say the least.

 

I should also note, I flew the A330 the other day, and this did not happen at all, and i also have not tried the IAE models, yet.

 

Will zip everything up and post when I'm done with this flight.

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  • Deputy Sheriffs

Alright, thanks. We'll try to have a look into it but unfortunately we have found that these speed drop issues on cruise are extremely hard to track down. 

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  • 1 month later...
  • 4 months later...

I have the A320/A321 Pro running on P3Dv4.5 (64 bit) and have been using it for a year or so with no issues. However two weeks ago I updated to v1.4.2 of the A320/A321 Pro and now have this speed problem. During cruise the managed speed dropped to 200Knt and continued to drop as the autopilot pitched the a/c up attempting to maintain altitude. Eventually the a/c hit the A-Floor speed and dropped from FL360 to FL200. I had to switch to Speed select and V/S to correct and regain altitude.

 

Has there been any new information or resolution to this problem?

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On 2/24/2021 at 3:24 PM, JetJockey said:

I have the A320/A321 Pro running on P3Dv4.5 (64 bit) and have been using it for a year or so with no issues. However two weeks ago I updated to v1.4.2 of the A320/A321 Pro and now have this speed problem. During cruise the managed speed dropped to 200Knt and continued to drop as the autopilot pitched the a/c up attempting to maintain altitude. Eventually the a/c hit the A-Floor speed and dropped from FL360 to FL200. I had to switch to Speed select and V/S to correct and regain altitude.

 

Has there been any new information or resolution to this problem?

 

I have found my problem. On the Init Fuel Planning page I entered the ZFWCG percentage but didn't enter the ZFW. I re-flew that same flight but entered both ZFW and ZFWCG and managed speed worked as expected. I flew this flight again only entered the ZFWCG and got the same reduced speed. However during the flight I entered the ZFW and immediately the speed increased to normal.

 

Problem Solved....

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