Plane pitches up and becomes uncontrollable and crashes

Question

While flying the Zibo 737-800 mod the plane about every 1 out of 2 times pitches up, stalls and crashes it happens. I tried to see if anyone had the same problem and saw one post which said something about de-icing the plane or something, tried it but still didn't work. It happens consistently at the top of descent. The same thing happened today and just as it happened before it crashed I quitted so it should be somewhere below on the log file, tried to find the problem but couldn't understand anything in the log file. If anyone is knowledgeable about this subject or could give any advice, please do as It has really been annoying me for this past week trying to find a solution, thanks in advance.http://questions.x-plane.com/?qa=blob&qa_blobid=4030393024380127746

Answer 1

Form your description, you could be right that icing may be contributing to the loss of control and crash.  Though it is odd that it always occurs at the top of descent.  And you said you have turned on the Wing and Engine Anti-Ice on the overhead panel?  What’s the outside temperature (TAT) shown on the Engine Display?

Inflight icing generally forms between 0 and -20 degrees C, with visible moisture (e.g., rain, in clouds).

Comments

Hello, thanks for trying to help I checked it from a saved file I had while on that flight from the log file about 10-15 minutes before it happened and it was -31C as shown. Am I de-icing it wrong? I on the three switches from the startup and switch and the engines switches to CONT. Sorry if I'm not very experienced, thanks for trying to help.

---

The three toggle switches in question are located at the mid-right section of the overhead panel.  They are marked: “WING ANTI-ICE” and “ENG ANTI-ICE 1 & 2”.

Try them and see if they make a difference.

P.S. -31 degrees may be a bit too cold for ice formation.  But it depends on how the sim is implemented.  I tested the Zibo for icing condition back in January, and it was modeled quite well.

---

Hello, the 3 switches I was referring to were those the wing anti ice and eng anti ice 1&2, sorry for not making it clear. So they don't  resolve the situation either. I think it could be that I didn't on the window heat switches at the back of the overhead panel, will try that and get back tommorrow, thanks!

---

Hello, the issue still happened today, I took some screenshots while it happened, while paused.

Image1

Image2

Thanks!

---

Was Image 1 taken after the plane had already become uncontrollable?

Icing shouldn’t be a factor since you had the Anti-Ice on.

Image 1 shows the aircraft was pitching up while in a 4950 fpm descent—which likely to be pulling some high G’s.  The IAS was entering danger zone.

I noticed when I exceeded the G limit on the Zibo, it will become uncontrollable.  Yet it would not show any pop-up to indicate structural damage.  However, it your plane were under autopilot at the top of descent. It shouldn’t have been pulling G’s.  I don’t have any idea…

---

Yes, image 1 was taken as the plane became uncontrollable, it then did the same thing like the other incidents, it went all the way up, stalls and nose dive for the ground.

I think this is a bug, but not sure why I'm the only one that has it and it makes it unplayable.

I think it's better of that I just use the default B737-800 for now, maybe till a later update.

Sorry for asking another question but no one answered my other threads and I couldn't find a solution on google:

Using the default B737 I have an alarm that I have no idea what it is, it is a constant beep every 1-second interval at about 10,000ft and above. None of the warning lights, lights up and I'm certain it isn't about the cabin altitude bug since that light doesn't light up. Shouldn't be about the speed too since I tried lowering it. I also tried verifying the integrity of my files and went into the B737-800 sounds folder and was unable to locate the same alarm. It's fine if you're unable to help me with this one, thank you.

---

Have you tried posting on the .org Zibo forum regarding the control issue?  It is frequented by plenty of experienced users.  Since the problem is repeatable, perhaps you can post a short video of the crucial moment and see if you can get an answer of whether it’s a known bug.

As for the default B738, I took the latest rev (11.36r2) up to cruising altitude a couple of times and had not encountered any “beeping” issue.  Since you've eliminated cabin altitude as a suspect, sorry, I can’t think of any reason.

---

P.S. I just noticed in Image1, the IAS was set to 330 in the MCP.  That’s pretty high!  In fact, when I tried it in the Zibo, it had limited my setting to 275 (at FL370).  You can also see that the redline for the IAS was indicated at ~280 kt.  Moreover, I believe the 737-800’s max speed is Mach 0.82.  The PFD was indicating 0.90.  I know the aircraft at this point had already gotten out of control, but what was the IAS and Mach speed just prior to that point.

My guess is the aircraft was suffering structure damage from overspeeding.  As I mentioned, the Zibo doesn’t seem to display any message to announce airframe damage, it simply goes unusual attitude on you when that happens.  I’d try easing back on the cruising speed to see if that would make a difference.

---

Hello, sorry for the late reply,

On the flight I took the image I had reached cruise level and had a speed of about 330 as shown on the autopilot, due to the stall it dropped, so you'r right on that.

Also just to confirm, I need to make sure the speed stays below 280kt and I'm below the red line as well as that the PFD indicates below 0.82 for my next flight, right?

If so I am quite sure it's the solution as it explains

Why it happens near descent and cruise timing as it's the time the engines have enough time to reach top speed and for damage and structure damage to occur.

It also explains why it happened 1 out of 2 times, as the only time it didn't happen was on a rather short flight and the speed didn't have enough time to reach 330kts or above 280kts and also it didn't have enough damage from overspeeding to be out of my controls.

I thought the speed limit was 350kts as only then the alarm for it would occur on the B737 on the Zibo mod and on the default and also didn't really expected it to be that realistic for strucure damage to occur as well as the loss of control. Will try it out on my next flight and get back soon, thanks for your help!

---

The Indicated Airspeed speed limit for the B738 (others as well for that matter), decreases with altitude.  Because the reading is “indicated”—not the “True” airspeed.  Up at FL370, 330kt IAS would probably be supersonic!

I don’t know how “realistic” is the simulation regarding overspeed structural damage.  I only hope it’s more forgiving than that in the real aircraft!

---

Hello,

I just completed about 500NM of flight hours (of just takeoff and cruise, will complete it tomorrow) staying under Mach 0.82 and it didn't happen as expected from my last post, which was reliving, thanks for your help!

I think I now know how to operate it while staying under Mach 0.82 after trying it while flying, it changes according to my pitch and calculates it with my TAS, so I basically have to stay under the red line.

I suppose the alarm on the default 737 is also regarding this issue.

I am almost 100% certain this is the resolution to the issue but will do a couple more flights and ensure it is resolved and will get back in a few days, thanks so much for taking the time to help. Would probably not have used the Zibo and default 737 without your help, therefore I'm very thankful to u for helping a stranger!

Answer 2

Hi ToyMasker,

You need to read the answer provided in the following link found at https://questions.x-plane.com/26025/intermittent-frame-rate-drop

Glenn