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Loosing speed midflight


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I have actually seen this two times I think.  I believe it is related to MSFS weather.  Both times I was using the sim's live weather and both times I was already at cruise and both times I had a sudden and major shift in wind.  The last time I went from a near 100 knot head wind to a near 100 knot tail wind.  I had issues with the stab trim going whacko for a good 50nm.  Then I was able to regain control at a lower altitude and climb back up to cruise and continue with no issues.  I am convinced that I was in some type of glitchy weather system being injected by MSFS.  I have never seen it using Weather Force and on 99.999% of my flights I don't see it even with sim weather. 

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  • 3 weeks later...

Today I had a problem which may be related to this. I was cruising fine at FL360 at M0.73 and then all of a sudden my speed was M0.55. The autopilot then started to trim up to maintain altitude. Then all of a sudden the speed went back to M0.73. It could be weather but not sure what is going on. Will try to replicate.

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49 minutes ago, John2 said:

Today I had a problem which may be related to this. I was cruising fine at FL360 at M0.73 and then all of a sudden my speed was M0.55. The autopilot then started to trim up to maintain altitude. Then all of a sudden the speed went back to M0.73. It could be weather but not sure what is going on. Will try to replicate.

Another idea, are you using real weather, if so there's an issue with it today where as you climb the OAT rises instead of decreases (reminds me of the FSX bug), although this issue is noticed right from take-off, well for me anyway

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52 minutes ago, EasternT3 said:

Another idea, are you using real weather, if so there's an issue with it today where as you climb the OAT rises instead of decreases (reminds me of the FSX bug), although this issue is noticed right from take-off, well for me anyway

I was using real weather but didn't notice OAT. I will try again...

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  • Root Admin

But weather is indeed another thing to keep in mind. Only yesterday did I got a 70 mph windshear while cruising along. AIS went from 250 to 320 in a second, of course the aircraft lost all civil behavior at that moment. 

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I did a flight from Montreal to Detroit last night and had this happen 5+ times to me in both directions (immediate drop and gain of speed) at FL320 and then again once during my descent. TheFlyingFabio had this happen a few times on stream yesterday as well. I don't think it's an issue with the aircraft, just crazy winds. I'm not knowledgeable enough about aviation to say if that's a bug in the sim or not, but it made the experience quite unpleasant. Bouncing back and forth between overspeed and way too slow in less than a second isn't fun.

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22 minutes ago, Aplato said:

I did a flight from Montreal to Detroit last night and had this happen 5+ times to me in both directions (immediate drop and gain of speed) at FL320 and then again once during my descent. TheFlyingFabio had this happen a few times on stream yesterday as well. I don't think it's an issue with the aircraft, just crazy winds. I'm not knowledgeable enough about aviation to say if that's a bug in the sim or not, but it made the experience quite unpleasant. Bouncing back and forth between overspeed and way too slow in less than a second isn't fun.

Yes, I think you are right that it something to do with the weather/wind. Asobo haven't quite figured that out yet. Happened to me again. Funny that I haven't yet experienced this with the A320NX which I have flown a lot recently.

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14 minutes ago, John2 said:

Yes, I think you are right that it something to do with the weather/wind. Asobo haven't quite figured that out yet. Happened to me again. Funny that I haven't yet experienced this with the A320NX which I have flown a lot recently.

I only noticed it starting yesterday, and only flown the 320nx yesterday and today and is massively affected, i.e 0 rate of climb/no ability to increase speed, hopefully asobo fixes the issue soon, 

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20 minutes ago, Aplato said:

It seems like it may be temperature rather than wind that is causing this problem for the past day or so: https://forums.flightsimulator.com/t/wrong-temperatures/424391/16

It is, (I've posted on that thread a couple times), it's very similar to a bug that was in FSX, I think although the temp is an issue, there's a wider issue with the weather system as a whole, as I noticed QNHs are off too

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Happened to me today with the 550 on a flight CYUL-CYQM. Cruising at FL390 at M0.76 and then all of a sudden speed is M0.56. No amount of thrust would bring speed back. Going to try the A320nx to see if it happens the same. Very weird. Forgot to look at the OAT. 

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  • CRJ Forum Moderator
vor 16 Stunden , John2 sagte:

Cruising at FL390

Seems quite high for the CRJ (yeah...I know specs list higher ALT but not loaded and in ideal conditions). I usualy fly default load up to about FL370 which didn't get me any headache so far. FL390 is close to the boundary and a sudden change in anything could lead to a unstable flight.

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1 hour ago, GEK_the_Reaper said:

Seems quite high for the CRJ (yeah...I know specs list higher ALT but not loaded and in ideal conditions). I usualy fly default load up to about FL370 which didn't get me any headache so far. FL390 is close to the boundary and a sudden change in anything could lead to a unstable flight.

You could be right. The autopilot actually stopped at FL370 and I had to VS it up to FL390. Simbrief gave me 39,000 so that's what I used but it could be pushing the envelope.

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Cruising at 390 in a CRJ.... you better be very light and the temps better be near perfect. I just would not do it as the envelope gets really really narrow at that altitude. 

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  • 3 weeks later...

I came across this problem yesterday during a flight on VATSIM. I made it to FL390 with anti-ice on but noticed the speed was dropping. I turned anti-ice off but the speed continued to drop. I immediately disengaged the autopilot and descended to FL350 to gain speed, but had to descend to FL310 before the jet recovered enough to maintain level flight and gain airspeed. I just assumed I had incorrectly set the jet up and got in the backside of the power curve and couldn’t recover without descending and gaining speed. I suppose this could be attributed to an icing bug with MSFS. I’ll watch that closer as I continue flying. 
 

However… Once the jet was stable at FL310, reengaging the autopilot would cause stab trim to drive full up. Just like Tribejagd’s video.  I tried resetting stab trim by pushing the buttons on the center console. I tried to use VS to put the jet in a slight descent. But every time I tried to reengage the autopilot it would drive full nose up stab trim.  I just continued the flight without autopilot.
 

What would cause the stab trim to go full nose up when activating the autopilot?
 

I turned anti-ice on once at FL310. It was on for at least an hour. I’d think that would be sufficient to remove any ice I might have prick up on the initial climb. The only thing I didn’t hit was the FD button. I won’t try FL390 in the future. 

 

https://forum.aerosoft.com/index.php?/profile/338048-tribejagd/

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vor 5 Minuten, Bryan Bedwell sagte:

However… Once the jet was stable at FL310, reengaging the autopilot would cause stab trim to drive full up. Just like Tribejagd’s video.  

Again...the thread is about "Loosing speed midflight" and not about the high pitch up when enabling AP!

 

Back to topic: FL390 is way to high for a loaded CRJ.

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@GEK_the_Reaper

 

i like to mention that when i had the “drop speed at altitude” issue i also encountered  weird trim reaction of the plane and could only fly manually because when engaging the AP i had full trim up.

 

this ONLY occurred when i had the speed issue ( it started with that )

 

so the 2 might be connected

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  • CRJ Forum Moderator

Dear @DGH,

 

up to this date we have not seen a valid proof of the fact that the CRJ looses speed at CRZ or can't climb. It was always either ICE, or weight and balance, or way to high CRZ ALT, or a binding which triggered the speed brake, or simply piloting error.

 

Please look in this topic where the same is discussed and also a video is shown (you can read my reply in that topic a bit further down). 

 

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@GEK_the_Reaper

 

well i have made 60 plus flights so far. Have my PPL and plying flightsims since 1990.


59+ flights did not have the issue and was happely flying at FL380 on multiple flights with no issues at all.

 

on just one or two occasions the dropped at cruise alt ( not recalling 100% but was 370 / 360 ish ) )  … no ice warnings  … no clouds … no spoilers … full throttle did not speed up so needed to drop the nose.
 

once at mach 0.74 i leveled of af few thousand feet lower And THEN the 15 degree trim issue started with the autopilot moving it.

 

with pilot error or wrong W&B i would have had issues way before i reached FL350. But even flew for a while completely stable at cruising ALT.

 

I never had the trim issue anymore … never had the speed issue. Never had them separate but only in combination.

 

hope this helps … but probably not.

good luck

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  • CRJ Forum Moderator

@DGH thank you for the explanation. As you wrote you have made 60+ flights and only once encountered the issue. I know these numbers are just figures and not accurate but enough for you (and others) to see how hard it is to reproduce it. None of the testers have had this issue!

 

Your case, since it happened only 1 time out of many flights, is different than the case of those complaining it happens ALL the time. Just look at all the postings from this thread and the one I linked you + other threads you can find on the forum, and you will find no recording of the issue. All recordings we have seen so far were (as you saw in the other video) piloting errors or something that triggered the spoiler axis (in another video you could clearly see in a ext shot that the spoilers were a bit open -not much but a bit and anough for the CRJ to loose speed at CRZ).

 

We have also already seen some strange weather behaviours like wind shifting, or strange temps,...all of which could lead to a sudden or slow speed loss at that CRZ level.

 

PS: Yesterday I checked the CRJ900 Air Nostrum Livery for something reported on the forum and I had 84PAX, 1.700Kg PL and 5000Fuel. I flown out of LOWI to the East. Simbrief gave me with these numbers a FL of 370 and I could barely make FL350 because ~30Kts tail wind. I still think that (depending on load and conditions) FL above 370 are a bit critical. A small change in atm cond and the CRJ will get out of balance.

 

So yeah...we are here and listen to you but we are unable to reproduce this thing.

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@GEK_the_Reaper

 

yes i understand what you are saying and yes i understand its difficult to reproduce ( and fix )

 

what i am saying is that the issue off SUDDEN speed loss at fl380 does not mean the airplane has a high load.

 

it would ( like you say ) not even reached that alt with max load or errors in W&B

 

W&B issues would not happily bring you to FL380 and then cruise happily for a while (and suddenly the speed drops.)

 

As i am typing 2 spannish CRJ are flying from canary islands happily at FL380 also … both on 2.5 hour flights ( more fuel ) and sure probably not 90 pax on board ( check Flightradar24). But perfectly done in RL.
 

but if you can reach in sim FL 380 with NO issues …. cruise with no issues … there should not be any reason the speed drops and the AP using 15 trim when engaged again after disengagement for example.

 

anyway … lets not overly discuss … again I understand the difficulty 

 

flying myself now from LIPE-EHAM T FL 380

 

 

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