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EEC ALTN mode cannot redline?

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Referencing a post that 777simmer made regarding the operation of EEC:

http://forum.avsim.net/topic/422006-autothrottle-disarm/?p=2808847

 

If the EEC fails then the FMC calculates the maximum thrust limit and then you have to watch out with MANUAL thrust!
Slamming the thrust levers full forward then, can cause an overboost (more than 90.000Lbs of thrust set) and can cuase engine damage.
The AT, when engaged, will not go beyond the FMC calculated limit, but you can with manual thrust!

 

I can't seem to go past the amber lines when EEC is failed (either by pushing the switches or selecting the failures).

Here's what the FCOMv1 had to say:

 

Thrust protection is not provided in the ALTERNATE mode and maximum thrust is reached at a thrust lever position less than full forward. As a result, thrust overboost can occur at full forward thrust lever position.

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Hi,

 

Overboost means you can set an N1 at which more thrust is developed than rated, more than the amberline.

So yes you could pass amber line.

However not redline. N1 and N2 limit protection is also available in the alternate mode!

If the N1 redlines, you actually have engine problems (EEC broken)....and you would have to do the "Eng limit, surge,stall" memory items and checklist!

 

To be able to pass that amber line you would have to be quite low I guess.

At high altitude there is no RPM (N1) at which the engine can produce rated thrust, it will produce less at high altitude.

 

What altitude did you try this at?

Try what happens if you do this in 5000ft or on ground.

 

I will do so as well later (europe time)


Rob Robson

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Hi,

 

Overboost means you can set an N1 at which more thrust is developed than rated, more than the amberline.

So yes you could pass amber line.

However not redline. N1 and N2 limit protection is also available in the alternate mode!

If the N1 redlines, you actually have engine problems (EEC broken)....and you would have to do the "Eng limit, surge,stall" memory items and checklist!

 

To be able to pass that amber line you would have to be quite low I guess.

At high altitude there is no RPM (N1) at which the engine can produce rated thrust, it will produce less at high altitude.

 

What altitude did you try this at?

Try what happens if you do this in 5000ft or on ground.

 

I will do so as well later (europe time)

Right, I cannot get past amber line even in EEC ALTN mode (both by pushing the buttons or failing the EEC via the failure options). I was in VHHH (which is basically sea level) and varied the weather from -169F to +169F to no avail.

 

 

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Ok, I have just tried in KJFK.

15C outside air temp.

 

undocked the engine instruments to a second monitor so I could see exactly what they do when swtiching EEC off and on again.

 

With my Saitek Thrust levers I get inconsistent results.

Sometimes I can go passed the Amber line (even with EEC on!) other times not.

 

Using F4 for full thrust is better/consistant.

With EEC I get exactly Amber line N1, which happens to sit right at 100% N1 (that is below redline)

With EEC off N1 moves past amber line to 102% which is overboost.

 

When I do the same in a winter them, OAT -5C, pressing F4 again.

With EEC I get again Amber line N1 but this is now reached at 96.5% (not at 100% because due to colder temps performance is now better meaning rated thrust is reached at a lower RPM.)

With EEC off I get 98.7% so again a slight overboost

 

Now are these slight overboost all the real 777 can do?

I dont know, I never tried :-)

But I would say this is modelled correctly.

 

Why are results with my Saitek thrust lever inconsistent?

I dont know.

If I slam my TL full fwd, with EEC on, then initially I get a bit more than amber line and then the EEC seems to regulate N1 back to Amber line.

If I then play/wiggle the TL a bit then I can wiggle N1 right into redline!

With EEC on that is!

That is not supposed to happen and DOES NOT happen with F4.

So I think it is the FSX controller that messes it up. (Have not tried FSUIPC)

 

Anyway, for me this is fine.

Normally you use TO/GA as max thrust. not Amber line.


Rob Robson

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Are you able to get to the red line by pushing the F4 key?

Only if I hold down F4. As soon as I let go, it goes back down to the amber-line, even with the EEC off.

Why are results with my Saitek thrust lever inconsistent?

I dont know.

If I slam my TL full fwd, with EEC on, then initially I get a bit more than amber line and then the EEC seems to regulate N1 back to Amber line.

If I then play/wiggle the TL a bit then I can wiggle N1 right into redline!

With EEC on that is!

That is not supposed to happen and DOES NOT happen with F4.

So I think it is the FSX controller that messes it up. (Have not tried FSUIPC)

Try pressing F4 very rapidly, if you time it correctly it seems there is an area between N1 redline and thrust overboost (amber line) both with EEC on and off!

I can understand how the throttles will revert back to amber-line if EEC is on, but even with EEC off there is still a big area between N1 overspeed and the position the throttles seem to go back to! You can especially see this if you use super low temperatures, since the gap between N1 limit and thrust overboost is large.

 

I thought the whole idea of Boeing philosophy is that the pilot can override the computers in an emergency. What if somehow a bug in EEC calculates a thrust overboost limit that is much too low for flight? The pilots would crash because they can't command maximum N1 thrust!

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Are you able to get to the red line by pushing the F4 key?

Only if I hold down F4. As soon as I let go, it goes back down to the amber-line, even with the EEC off.

 

Why are results with my Saitek thrust lever inconsistent?

I dont know.

If I slam my TL full fwd, with EEC on, then initially I get a bit more than amber line and then the EEC seems to regulate N1 back to Amber line.

If I then play/wiggle the TL a bit then I can wiggle N1 right into redline!

With EEC on that is!

That is not supposed to happen and DOES NOT happen with F4.

So I think it is the FSX controller that messes it up. (Have not tried FSUIPC)

Try pressing F4 very rapidly, if you time it correctly it seems there is an area between N1 redline and thrust overboost (amber line) both with EEC on and off!

I can understand how the throttles will revert back to amber-line if EEC is on, but even with EEC off there is still a big area between N1 overspeed and the position the throttles seem to go back to! You can especially see this if you use super low temperatures, since the gap between N1 limit and thrust overboost is large.

 

The FCOMv2 says this:

Thrust protection is not provided in the alternate mode and maximum rated thrust is reached at a thrust lever position less than full-forward. As a result, thrust overboost can occur at full forward throttle thrust lever position. The EICAS causion message ENG LIMIT PROT (L, R) is displayed if the thrust lever position commands an N1 greater than the maximum rated thrust (maximum N1). N1 and N2 red line protection is still available in the alternate control mode.

There is no way right now you can get this EICAS caution message to show up. Even in EEC ATLN mode, you can fly around for hours without tripping this message because the throttles are not allowing you to go past amber line unless you hold down F4.

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Only if I hold down F4. As soon as I let go, it goes back down to the amber-line, even with the EEC off.

 

I tried that also but could not get passed amber line with EEC on. Just like it is suppose to. Dont know why you get a different result.

 

 

"I dont think that is actually overboost. The FCOM says that the FMC calculates the maximum rated thrust when the EEC fails and that this is supposed to be always slightly above the EEC calculated one. "

 

Anytime you are above amber line you have an overboost situation. No matter if you 0.5% N1 above it or 5%. The FMC does not calculate max rated thrust. As far as I know the EEC still calculates this (if it can).

The FMC calculates only reference/target N1.

Reference N1 = your green CLB/CRZ/CONT limit

Target N1 = replaces the green Ref N1 symbol by a magenta symbol, meaning that the FMC is calculating this value cause you are in Vnav.

The reason they put in the book that FMC calculating values are above EEC calculated is values is so that you know that you have sufficient thrust (more, not less) and as a warning. Be carefull...FMC values are greater at the same TL position....be carefull you dont overboost it.

 

"Try pressing F4 very rapidly, if you time it correctly it seems there is an area between N1 redline and thrust overboost (amber line) both with EEC on and off!"

 

But why would you do that? You press F4 once and you get full rated thrust!

A real world pilot would slam his throttle fwd once (not repeatedly) and he would get max rated, amber line thrust.

Can you imagine a pilot going slam slam slam slam? I would ask him if everything is ok with him!

Granted pressing F4 repeatedly should never give you more than amberline with EEC on (definately not Redline) but it is something so far from real to keep hitting full thrust...full thrust....full thrust....full thrust...that maybe PMDG did not think of people actualy doeing something like that. Or...maybe its how the real thing behaves...but I have never tried ;-)

 

"I can understand how the throttles will revert back to amber-line if EEC is on, but even with EEC off there is still a big area between N1 overspeed and the position the throttles seem to go back to! You can especially see this if you use super low temperatures, since the gap between N1 limit and thrust overboost is large."

 

When using F4 or when using your thrust levers?

With F4 I get a small overboost and it does not go back, it stays at overboost.

With TL I get unconsistant behavior.

Just because the EEC are off that does not mean your N1 RPM can be moved all the way up to or just before N1 redline.

With EEC, off the engine will give what it can give. If that is 102% so be it, if that is 105% then good for you. I dont know how much more the engines are capable of. Do you?

I do know they will not go to redline (real world) unless you have an engine problem!

 

"There is no way right now you can get this EICAS caution message to show up. Even in EEC ATLN mode, you can fly around for hours without tripping this message because the throttles are not allowing you to go past amber line unless you hold down F4"

 

Like I said, anything above amberline is an overboost.

Look at the Eng Limit Prot L/R checklist in the QRH.

It tells you to move the thrust levers back to below amber bar.

Conclusion...above Amber Bar = overboost

Below Amber Bar is not.

That checklist does not show unless the EEC are in alternate mode either as it clearly states under "condition". Meaning that my 2% N1 increase when EEC are switched off IS in fact a small overboost. It is not an OK FMC value!

 

But you are correct that I dont remeber the Eng Limit Prot L/R popping up either. And I think it should have. Maybe this is not simulated. We would have to ask PMDG. For me no big deal if it is not simulated.

Sorry, but my responses ended up in the middle of your post I quoted.

Dont know how to respond to your multi quote post correctly.

 

I might be able to dig some more up in the maintenance manual....but I think we are getting into stuff then where we are both just experimenting/guessing.


Rob Robson

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I don't think people should necessarily expect every detail of the FCOM to be in the simulation. It's quite possible FSX limitations prevent some things from being simulated. I asked PMDG support about red exceedance indications on EICAS I got after takeoff once and they said the EEC limits were hardcoded in the sim so they can't be exceeded. However if you slam the throttle forward (or hold F4 down) you can see the commanded N1 go to maximum. Holding F4 down is effectively trying to bypass PMDG's engine simulation.


ki9cAAb.jpg

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Holding F4 down is effectively trying to bypass PMDG's engine simulation.

Exactly. That was kind of what I was trying to get at.

Rob Robson

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I don't think people should necessarily expect every detail of the FCOM to be in the simulation. It's quite possible FSX limitations prevent some things from being simulated. I asked PMDG support about red exceedance indications on EICAS I got after takeoff once and they said the EEC limits were hardcoded in the sim so they can't be exceeded. However if you slam the throttle forward (or hold F4 down) you can see the commanded N1 go to maximum. Holding F4 down is effectively trying to bypass PMDG's engine simulation.

 

I highly doubt this is an FSX limitation. It's more like they forgot to program the "throttle limiting mechanism" to take into account that it shouldn't limit to amber line when EEC is in alternate mode which is quite strange considering they took the time to program the FMC to calculate the alternate N1 schedule.

 

It's a shame because the exterior and VC models are quite nice and super detailed, but it seems that some of the systems weren't treated with the same level of care.

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I highly doubt this is an FSX limitation. It's more like they forgot to program the "throttle limiting mechanism" to take into account that it shouldn't limit to amber line when EEC is in alternate mode which is quite strange considering they took the time to program the FMC to calculate the alternate N1 schedule.

It's a shame because the exterior and VC models are quite nice and super detailed, but it seems that some of the systems weren't treated with the same level of care.

I am not sure why I am answering to this post because you seem to choose to totally neglect everything I/we are posting anyway.

 

1) Pressing F4 over and over again is not normal. It is insane and seems to bypass PMDGs engine simulation.

I dont know if the inconsistant TL behavior I have is an FSX problem or something PMDG can fix. I will have to investigate further before I ask PMDG if my TL behavior is wrong or not.

 

2) One press of F4 with EEC on gives me amber line which is according to the book.

 

3) One press with EEC off give me more than amberline which is also according to the book. It does not limit to amber line with EEC off. I dont know what you are doing wrong but I definately do get an overboost.

 

The other remaining thing is possibly the missing Eng Limit Prot L/R engine EICAS message which I will try to trigger when I am back home again.


Rob Robson

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I am not sure why I am answering to this post because you seem to choose to totally neglect everything I/we are posting anyway.

 

1) Pressing F4 over and over again is not normal. It is insane and seems to bypass PMDGs engine simulation.

I dont know if the inconsistant TL behavior I have is an FSX problem or something PMDG can fix. I will have to investigate further before I ask PMDG if my TL behavior is wrong or not.

 

2) One press of F4 with EEC on gives me amber line which is according to the book.

 

3) One press with EEC off give me more than amberline which is also according to the book. It does not limit to amber line with EEC off. I dont know what you are doing wrong but I definately do get an overboost.

 

The other remaining thing is possibly the missing Eng Limit Prot L/R engine EICAS message which I will try to trigger when I am back home again.

It seems you are not understanding what i believe to be wrong with the EEC alternate model.

 

The FCOMv2 says clearly that only N1 RPM protections remain in place after EEC alternate mode, you can thrust overboost as much as you want (because protections are lost), not some arbitrary FMC calculated X% limit over 100% N1. You can't get anywhere close to the N1 RPM limit, which as yourself has previously stated in the other thread is the red line.

 

This "bug" in the limiting to the FMC value is exactly why Eng Limit Prot L/R warning isn't being triggered.

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I highly doubt this is an FSX limitation. It's more like they forgot to program the "throttle limiting mechanism" to take into account that it shouldn't limit to amber line when EEC is in alternate mode which is quite strange considering they took the time to program the FMC to calculate the alternate N1 schedule.

 

It's a shame because the exterior and VC models are quite nice and super detailed, but it seems that some of the systems weren't treated with the same level of care.

If you select EEC ALTN you can set a higher N1, about 2% more, so I don't think PMDG have forgotten anything. I'm not sure what you expect to see, and how much relationship that bears to reality. If the additional N1 isn't as much as the aircraft there could be a good reason for that, such as FSX limitations.

ki9cAAb.jpg

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