Loss of thrust during Cruise

[snapshot21 23]

Hi,

I was cruising at an altitude of 33000 ft during a flight from KSAN - KRNO. ZFW was 30,000kg and CG was within the green. As I was constantly alt-tabbing during flight, I suddenly noticed my speed going down in level flight with N1 near max cruise thrust.

Here is the screenshot of the point that I noticed it. The plane was pitching up to try to maintain altitude.

 

I let the plane figure itself out but it never recovered.

 

 

I set takeoff thrust and even then it was still falling like a rock and losing altitude.

[Herman 832]

Likely behind the power curve. Once you let the speed decay and the AOA build up (inferred from the pitch attitude in level flight) as the pictures show, there's nothing to do but drop the nose (a lot) and gain speed that way. You've got too much drag at that AOA to accelerate in level flight even at MCT. Or as you saw, even maintain altitude. Instead of thinking pitch for altitude (which your autopilot was also doing) and thrust for speed as usual, the only way to regain energy/speed is to pitch well down and descend. See this about Pinnacle 3701 who forgot some pretty basic airmanship in a situation somewhat like yours.

 

SkyWest airlines got themselves some max cruise altitude limitations for a while from FAA for a couple of these over a relatively short time. Pretty much what you saw in your situation. They made the necessary corrections in their training and culture to fix the issue and they're fine now. 

 

You might also consider changing the title. You had all the thrust the airplane had to offer. Thrust isn't why you got you so slow, AOA is.

[snapshot21 23]

58 minutes ago, Herman said:

Likely behind the power curve. Once you let the speed decay and the AOA build up (inferred from the pitch attitude in level flight) as the pictures show, there's nothing to do but drop the nose (a lot) and gain speed that way. You've got too much drag at that AOA to accelerate in level flight even at MCT. Or as you saw, even maintain altitude. Instead of thinking pitch for altitude (which your autopilot was also doing) and thrust for speed as usual, the only way to regain energy/speed is to pitch well down and descend. See this about Pinnacle 3701 who forgot some pretty basic airmanship in a situation somewhat like yours.

 

SkyWest airlines got themselves some max cruise altitude limitations for a while from FAA for a couple of these over a relatively short time. Pretty much what you saw in your situation. They made the necessary corrections in their training and culture to fix the issue and they're fine now. 

 

You might also consider changing the title. You had all the thrust the airplane had to offer. Thrust isn't why you got so slow, AOA is.

 

What I want to know is how the plane got in the situation in the first place. It was basically at .74 mach at cruise flight and A/P set and stable before I alt tabbed. Payload and fuel are well within limits and I was only at 33,000 feet. I was already at cruise for around 15 minutes before I alt-tabbed. Then after I returned the speed is at ias 150 and struggling to maintain altitude.

 

Or is there failures modelled here that I dont know of. Icing perhaps?

[Herman 832]

At that altitude range for that airplane, you have to stay on top of the airspeed. Once it starts to bleed off and you lose much more than 20 KIAS, it starts to run away from you. Watching the Mach won't do it because it's too coarse. Also, any turbulence or warmer than standard temp just makes it easier to slow down and get into the cycle. As you noted  earlier, the autopilot will try to pitch up to correct for altitude loss. That's what it's designed to in IRL and in the sim. Increasing AOA adds drag which builds quickly at that altitude at cruise AOA, and which has to be overcome by power. Since the engines are close to their limits at that altitude range, they have a hard time accelerating quickly enough to stay up with the speed decay. That's what happened with the SkyWest scenarios, and why the FAA's response was to limit max cruise altitudes and institute min cruise speeds until crew awareness and response was improved. Which one were you flying in your scenario? Do you remember if there was turbulence, even gentle  mountain wave type stuff? Temp deviation from ISA?

 

This article I believe correctly states the series and limitations that were imposed. It accuratly notes that the event that got the attention was an unexpected and unplanned 4,000 foot altitude deviation. And BTW, icing was never a factor in any of the SkyWest events.

[Hoffie3000 21]

Take a look at the trim Setting. Your Pictures shows up values from 10 (first Picture) to 15 (second Picture)- way to much.

How do you trim - Yoke or Keyboard?

 

Normally I trim with Keyboard buttons but my observations during high Speed stall (CRJ Version 1.03) is that you have to use the trim button on the yoke to set trim Settings (down or up) back in the right trim window due Keyboard buttons do not handel these high values. If your trim Settings are in normal range Keyboard trimming will work again.

[Herman 832]

To add to my earlier post, do you remember if you used the correct climb speed schedule? If you read the NTSB report on the Pinnacle accident, the crew climbed at too low a speed, which never gave the aircraft a chance to accelerate to the appropriate cruise speed. I can't tell from your upper picture if that was in cruise or after you already realized you were too slow. As the news article stated, FAA added cruise speed requirements to provide additional margin to recognize and recover from speed decay. Looks like min cruise speed was around 235 KIAS for the older ones (200s) and 250 KIAS for the 900s. Looking at your two pix, you were way slow.

[snapshot21 23]

18 minutes ago, Hoffie3000 said:

Take a look at the trim Setting. Your Pictures shows up values from 10 (first Picture) to 15 (second Picture)- way to much.

How do you trim - Yoke or Keyboard?

 

Normally I trim with Keyboard buttons but my observations during high Speed stall (CRJ Version 1.03) is that you have to use the trim button on the yoke to set trim Settings (down or up) back in the right trim window due Keyboard buttons do not handel these high values. If your trim Settings are in normal range Keyboard trimming will work again.

 

That was set by the A/P due to the nose up command of the FD. I did not touch the aircraft again during the situation as I chose to just continue watching a youtube video instead of rectifying the situation lol.

 

3 minutes ago, Herman said:

To add to my earlier post, do you remember if you used the correct climb speed schedule? if you read the NTSB report on the Pinnacle accident, the crew climbed at too low a speed, which never gave the aircraft a chance to accelerate to the appropriate cruise speed. I can't tell from your upper picture if that was in cruise or after you already realized you were too slow. As the news article stated, FAA added cruise speed requirements to provide additional margin to recognize and recover from speed decay. Looks like min cruise speed was around 235 KIAS for the older ones (200s) and 250 KIAS for the 900s. Looking at your two pix, you were way slow.

 

I was using the CRJ 900. It was during cruise already. I climbed with 250 knots and 290/.74mach as I set it on the FMC. I climbed with SPEED Mode. Climb phase was normal and the aircraft followed LNAV perfectly. I was already at cruise for about 15 mins before that incident. I also dont think I was behind the power curve because earlier in the cruise I was gunning the engines and was able to get .82 mach before slowing down to a more reasonable .74-.78mach. The throttles was at MCT because I tried to catch the speed before taking the screenshot. But it was at about 80% N1 during cruise and maintaining the said .74mach. It was not in a mountainous area and the wind was a stable 84 knot crosswind

 

Ill try the flight again and see if I get the same result.

[Frank Docter 5011]

In an aircraft without autothrust it can be difficult to maintain a cruise airspeed while watching YT videos. It could very well be that the speed dropped to an too low value during your YT breaks and as a result you got the high AoA etc. 

 

Reasons for the speed drop can be internal and external. My advise would be to fly an ATHR aircraft when watching YT or check on your aircraft more frequently. 

 

If it happens again when not doing other duties please report again. 

 

Thanks

[Herman 832]

10 hours ago, snapshot21 said:

 

...I was already at cruise for about 15 mins before that incident. I also dont think I was behind the power curve because earlier in the cruise I was gunning the engines and was able to get .82 mach before slowing down to a more reasonable .74-.78mach. The throttles was at MCT because I tried to catch the speed before taking the screenshot. But it was at about 80% N1 during cruise and maintaining the said .74mach. It was not in a mountainous area and the wind was a stable 84 knot crosswind

Thanks for the detailed response. Your climb procedure looks good, so you didn't make the same tragic mistake the Pinnacle crew did. Your comment about "gunning the engines" before decelerating shows at that point you were not behind the power curve. Later however, when you got too slow, the drag rise was quicker than the thrust increase you could command. That's when you were behind the power curve.

 

Frank's suggestion about using an autothrust aircraft if you want the sim to run in the background while watching YT vids is a good one. So too is your suggestion to retry the flight (without ALT+TABing in and out) and see if the issue repeats.

[Hans Hartmann 1742]

One thing: The speed trend vector on the PFD only shows when the acceleration/deceleration is more than 3 knots in the next 10 seconds. It's possible that the speed increases/decreases slowly without the speed trend vector showing. As Frank and Herman said, in an aircraft without autothrottle you need to constantly watch your speed and correct the throttle settings accordingly.

[Mathijs Kok 29643]

And that is why the CRJ is more fun to fly then a Boeing or Airbus, you got to pay attention.

[Herman 832]

10 minutes ago, Hans Hartmann said:

One thing: The speed trend vector on the PFD only shows when the acceleration/deceleration is more than 3 knots in the next 10 seconds. It's possible that the speed increases/decreases slowly without the speed trend vector showing. As Frank and Herman said, in an aircraft without autothrottle you need to constantly watch your speed and correct the throttle settings accordingly.

Excellent point, Hans. The speed trend vector cue was something that some crews were expecting to alert them to speed decay instead of actually monitoring and correcting the primary cue, the airspeed.

[metzgergva 30]

I just want to add that sometimes the OAT is changing in cruise and depending on weather app used, I have seen too warm temperatures high up. That may lead to a significant power loss.