ATR VNAV IAS speed it too low causing "speed speed" warning during climb

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1

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no

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yes

Which aircraft are you reporting an issue about? (Please also add the proper tag for it)

ATR 42 / 72

Which aircraft version are you experiencing this issue on? (You can find this listed in the Content Manager under the Aircraft Name)

latest

Brief description of the issue:

When climbing to cruise altitude with IAS I realized that the VNAV IAS speed is too low and below the minimum speed for the altitude. The magenta speed in the PFD is fine, but the one IAS is following is the IAS from VNAC which is too low.
In the example magenta speed in PFD is 177 and VNAC IAS is 160. When flying IAS speed is then too low and “speed speed” warning is displayed.

Provide Screenshot(s)/video(s) of the issue encountered:

Imgur

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Detailed steps to reproduce the issue encountered:

Start at EDDS and fly TAGI4B departure, climb to FL200 using IAS with automatic speed (magenta).
I had icing conditions selected and anti ice activated, but probably does not make a difference.

PC specs and/or peripheral set up if relevant:

4070

Build Version # when you first started experiencing this issue:

latest

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Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

2

Seen this, however I’m not an expert to say if it conform to the real aircraft or not, so the next times, I’ve added a bit more of Trim to compensate and no more aural alert … if it helps :wink:

3

It can also be avoided by setting a manual speed, which is then automatically adapted to a changing minimum speed.

What I find especially odd is that the magenta speed in the PFD and speed on the VNAV page is not the same. I thought the magenta speed is exactly that?

4

Since 1.0.36 I was in the process to handle the ATR again after a long time, specifically around the startup and shutdown sequences. So, for sure I didn’t pay attention too much to the flight data. After the fun I have to go deeper in the checks and analysis. I will try to understand this part and how it behaves these upcoming hours.
I have to check in this situation if there’s any effect on IAS vs VNAV mode and get a proper idea of what could make the difference. Will try to report my find soon. Indeed other simmers will bring here their own statement.

5

I would say indeed the reference would be the FMS, without touching anything from takeoff until TOC, I mean without touching SPD. So the FMS will apply velocity with flight path in reference, this is how I see things … now to the current behavior in the sim … :thinking:

Ok, had to make some arrangement in my setup outside the sim itself, prior to start the flight …
Also had a fight with Simbrief planning, in order to get the expected flight path profile. great tool which however is lacking of a simple and proper way to select SIDS and STARS easily, as we’re used to with LittleNavMap. It only suggest us a few which aren’t really what we want, and the manual route entry is denying some points which are correct following the current AIRAC … anyway … on the way :wink:

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[EDIT] Indeed, it looks like we are a bit limited on the way we are allowed to prepare the VNAV profile, there’s some waypoint specific values which are accepted as input values on the MCDU, but not displayed in the flight plan and some other entries which are not allowed, I currently not found a solution and how this would be overridden on our side … :face_with_raised_eyebrow::thinking:

6

Having a closer look at your parameters , maybe GW is a little too “light” (18000 kg) , even for a -42.
Try entering a higher GW to see if better

7

Still not able to find a solution to set the FMS for higher speed
ALT is ok though for the short hop I’ve planned

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and the speed is set to 9 kts in the FP :open_mouth:
sure I’m doing something wrong :thinking:

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I’m using Simbrief and FP / FUEL / PAYLOAD has been sent from the EFB without any issue …

8

Ok, it looks like we have to enter data waypoint by waypoint, one at a time. Not used to with some other aircraft and MCDU automatic flight path calculation

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… anyway, speed for TO seems set to 120 on PFD accordingly to VNAV page

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So, I have to check along the flight how it behaves

9

Eventually got a 178kts on climb
The point is to ensure LNAV is engaged, then VNAV is engaged as well
Now following FP :

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After this I’ve tried an RNAV approach with V-FP displayed, however the descent didn’t occurred. Not had time to notice exactly, though I guess I didn’t manage properly the approach and was too high before FAF. The Speed was correct, though I had to manage it manually on approach.

I guess it will take time until I perform the proper actions sequence. A bit disappointing not to get the cursor position, between bad actions and potential current bugs or incomplete process in the FMS and flight plan management ???

Well I guess my target altitude was incorrect on approach, so I will retry again …

10

Hmmm… I wonder why you think it is light? Max takeoff weight is 18770 KG for ATR 42. With 18 tons it is actually quite heavy already.

What makes me believe that there is a bug is that the magenta speed displayed in the PFD should be the one that is used to define the rate of climb with IAS active. If it is not, then this is highly misleading and I doubt that it would be like this in the real aircraft.

I think it is important to note that I observed the discrepancy during climb to higher altitude (e.g. from FL100 to FL200) and with a heavy aircraft.

11

OOPS !! OK I’m wrong

Here’s what I thought.
If the aircraft is too heavy compared to what is entered into the FMS, it will not be able to follow the indicated speed and rate of climb.

12

Again today:

This time PFD Auto SPD TGT is correctly set at 160 but VNAV TGT speed, and the speed IAS is following, is set at 136, way too low for clean configuration. And yes, I know I forgot to switch to power setting to CLB :slight_smile:
Edit: when repeating the flight and setting the pwr mgt to CLB then VNAV also has 160 as target. Still confusing that they differ and the actual target speed is not displayed.

Another surprise was when I tried to climb with VS and at one point reduced target VS to 0 it did not follow this but instead continued to climbed with 2900ft/min, resulting in a critical speed.

And if you are wondering if the VS did eventual go down the answer is NO. Only after changing the VS speed to something else and then back to 0 it finally reduced the VS.

Really not sure what is going on there.

13

Hmm… Interesting thought. But I initialize the weight page with the correct values by long pressing the buttons and ensured that the weights are aligned everywhere. And there are some inconsistencies with the payload loading at the moment as reported elsewhere.

14

After doing a couple of starts and climbs I think this is what happens:

  • VNAV TGT IAS is the one that is used by the “IAS” mode, not the AUTO SPD TGT displayed in the PFD
  • VNAV TGT IAS does NOT take into consideration the current altitude and always uses 160 irrespective what the current minimum speed is due to altitude and weight.
  • PFD SPD TGT actually does take those into consideration and shows the correct speed, which is unfortunately not used.

I’m pretty sure that before this update there was not a problem with this. Either because IAS followed the PFD speed or that the VNAV speed actually was correcting for the current altitude / weight and minimum speed.

Btw. did somebody notice that in the VNAV page it does say 160FT instead of 160kt ?

And I have an easy way to reproduce this issue:

  • Setup weight close to max weight (e.g. 18.1 tons).
  • Climb to FL100.
  • Note magenta target speed and tgt ias speed from VNAV page. Both should be the same, in my case 240kt
  • Initialize a IAS climb to FL180
  • Note the magenta speed, it should be just above the too slow band starts (for me 164 and increasing with increasing altitude).
  • Note the VNAV page TGT IAS speed, it will be 160.
  • IAS will set climb rate to reach 160kt, way too slow at e.g. FL150.
  • SPEED SPEED warning will start relatively soon

I just know that it was not like this before the update. How the real ATR behaves I have no idea, but maybe somebody who has hands-on experience could chime in.

1 Like
15

Thanks for explanations with clarity ! I’m not at the level to be able to decipher easily and report with such simple words. I just have the feel the aircraft is better on a few parts since 1.0.36, though very strange in many area. I guess it will take again one or two more Aircraft Update releases until we’ll be able to perform standard actions with smoother and expected behavior …

17

I have the same Speed problems in climb with the ATR.
No solution at the moment ?