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Can't maintain my speed FL390 - STALL!


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Hi,

 

Suddenly I couldn't maintain my speed and almost stalled. Nothing was wrong as per my opinion. And my throttle was even on TOGA at some point.

 

I tried to lower my FL to 370 but same issue, ended up to request my descent early to finally get back with a normal speed as lower I was going.

 

Any idea?

da2a981acc08419ca46e39379922b1cd.jpg

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  • Tbo changed the title to Can't maintain my speed FL390 - STALL!

What was your aircraft weight?  Just because the plane is rated for that flight level doesn't mean it should be flown there.  I did two flights yesterday at FL390 with zero issues, however....

 

1. Check your icing in the sim is set to visual only.  I am not sure if it has been fixed with the latest update, but the in sim icing has been notoriously aggressive.

2. TOGA for take off.

3. At the acceleration height, pitch down for speed and select CLB on the thottles.

4. Pitch to maintain 250 kts (or use the AP) until 10,000 ft then...

5. Increase speed to 290 kts until the transition (where 290 kts is equal to .74 mach)

6. Continue climb at .74 mach to cruise.

7. I allow the speed to increase at cruise to about Mach 0.80 (I cruise a bit fast but well under the barber pole"

8. Throttles to Manual and monitor to hold speed.

 

You cannot set a speed at cruise and walk away.  Crap will happen that requires you to increase or decrease the throttles at cruise (wind shifts for example).  If you are not watching it your plane can bleed speed while trying to maintain an altitude.  This will cause the plane to trim nose high and bleed even more speed.  The CRJ does not have the power to firewall the throttles and correct.  If you get behind the curve your only option will be to trade altitude for speed.  If this happens, stay at whatever altitude you are able to correct the speed at and continue the flight. In the picture above you are close to a power on stall.  Stalls are not solved by more power, but by lowering the nose.   However I cannot stress enough that this aircraft is only half automated.  The installed auto throttle is a PHONT AMT model.  Put Hand On Throttle and Move Throttle.....

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1 hour ago, Tbo said:

My TOW as 30315 kg

 

So I watched my stream and I guess it started here: https://www.twitch.tv/videos/1187678890?t=01h06m52s

The plane suffered of some rudder mouvement, lost some altitude and speed started to decrease.

 

1: At ~30.000kg FL390 is a bit on the edge, you can get there but don't have much performance left.

2: Consider cruising at a bit higher speed, at least M.77 above FL360.

3: This seems to be a sudden shift in weather at altitude. You can see the wind shift instantly on your MFD, temperature changes as well.

 

Airplane tries to get back to FL390, loses speed to below minimum drag speed and at that point you have kind of lost the battle unless you regain speed by adding thrust or trading some altitude. Since you were already close to the limit in terms of performance and did not add enough thrust soon enough, the speed drops more and even TOGA thrust does not overcome the extra drag. So you have to pitch down and trade altitude for speed. Vertical speed mode and a moderate rate of descent will not work, you have to properly pitch down.

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Nothing wrong with that, it can actually reach it and with the tailwind you had it was probably beneficial. But you have to make sure to keep the speed up a bit then as well, and of course in real life the wind and temperatures do not change that sudden.

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53 minutes ago, Tbo said:

Thanks for your analysis I understand now.

Also I used simbrief - so it put me that FL with that weight. 😕

SB is great for a lot of things, performance calculations is unfortunately not one of them. SB will just give you a Flight Level, if you can obtain it, is your responsibility as as captain to find out

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Mathijs Kok
This post was recognized by Mathijs Kok!

Crabby was awarded the badge 'Great Content'

I use Simbrief but have noticed, especially lately, that with the CRJ it tends to plan to extreme FL regardless of weight or distance.  I had it plan a 175 mile flight from PASI to PAKT at FL370.  In the real world the PIC would is the ultimate responsible party when it comes to how the aircraft is dispatched and flown.  Don't go down the automation rabbit hole.   A performance calculation is already in the EFB.  A performance calculator will give you Vspeed info for take off and landing.  It does not give you cruise, at least none of them that I have seen.  

 

Looking at the video, you were already bleeding speed prior to the "event".  It was slight but nonetheless bleeding.  The event that I saw was a sudden change in wind direction/speed and that was coupled with a pressure change.  At 107 minutes the pressure change was almost 1000ft.  So the plane began a climb while it was pretty slow.  At 108 you can see you are in a very vulnerable low energy state and the plane is struggling to regain FL390 and nose high.  After that the plane was trying to tell you that it needed to be lower to get faster.  As pilot, you seemed to be locked in to maintaining altitude.  Remember trading altitude for much needed airspeed is always an option, until it is not.  Airflow over the wing is a pilots best friend because it allows for controlled flight, no matter the altitude.  So, if you are in that situation again, AP off, drop the nose, acquire the airspeed you need.  If the flight is ling enough, you could (depending on weight) attempt to cruise climb back up, but you risk not have the wanted amount of fuel during approach for hold or go-around contingencies. 

 

I have learned not to leave the CRJ unattended and this goes back to P3D.  I can't tell you how many times I got to cruise and everything was fine, went to make a sandwich.  Upon returning I find my aircraft floundering or in a big hole in the ground.  You obviously did not leave it unattended, but the corrective action taken (fight to maintain altitude) was not correct.  Great thing about simulation is we get to live and learn instead of becoming a case study for some commercial pilots course. 

 

 

 

 

 

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I'll talk to the people at Simbrief as they plans they make for the CRJ are very 'optimistic'.

 

As Crabby said, this is a flight simulator. You are the pilot. If something does not work do not try to force it or try to find what is the cause, simply solve the issue. Fly the aircraft. 

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6 hours ago, Crabby said:

I use Simbrief but have noticed, especially lately, that with the CRJ it tends to plan to extreme FL regardless of weight or distance.

 

I don't think this is a new thing, but yes, I agree -- SimBrief routinely generates unrealistically high cruise altitudes. To work around this I just find a corresponding flight on Flight Aware and enter the cruise altitude used there instead of AUTO in SimBrief.

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