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AzN1337c0d3r

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)

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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.

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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.

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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.

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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.

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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.

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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.

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If you select EEC ALTN you can set a higher N1, about 2% more. I'm not sure what you expect to see, and how much relationship that bears to reality.

FCOMv2 says you can select up to N1 RPM limit (i.e. red-line) as all thrust protection limitations are lost, not some arbitrary 2% more.

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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 2% limit over 100% N1. You can't get anywhere close to the red line, 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.

I do understand what you are saying.

If you are unwilling to accept a mere 2% overboost as an overboost then I can not help you any further. I call that denial, not a bug.

 

I mean what sort of overboost would make you happy then?

103%

104%

105%

106%

107%

108%?

109% = redline = engine limit/surge/stall checklist = pull back throttle

 

There just is not that much more you can get out of them engines past Amber Line.

Not without the risk of doing some major damage to them at N1 Redline.

Is that what you are looking for? You want to see if you can blow them appart?

Yeah maybe they did not simulate that part :-)

 

I looked into the 777 maintenance manual but found no helpfull further info.

You would need a GE manual which I dont have.

 

As far as I know you should never ever ever get close to Redline N1 even in alternate EEC mode. Unless that engine has a problem BEYOND the EEC being in alternate mode.

But like I said I have no data to prove me wrong or right. I dont know if it can do 103% or 105% or 107% with EEC off. And neither do you. So we can not say this is simulated correctly to the last bit or not.

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FCOMv2 says you can select up to N1 RPM limit (i.e. red-line) as all thrust protection limitations are lost, not some arbitrary 2% more.

I dont have the PMDG FCOM with me but I am pretty sure there is no difference between that and my personal FCOM. Which clearly states that N1 and N2 limit protection (redline) is available also in Alternate mode. That means that you can get passed the amber line and if there is some sort of an additional engine problem (governor for example) which would result in RPM increasing to redline then the EEC will prevent this by commanding reduced fuel flow. So no...you can not go up to N1 red line.

 

I hope you dont mind, but I have no further info on this subject.

Maybe a GE engineer can pickup from here ;-)

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I do understand what you are saying.

If you are unwilling to accept a mere 2% overboost as an overboost then I can not help you any further. I call that denial, not a bug.

 

I mean what sort of overboost would make you happy then?

103%

104%

105%

106%

107%

108%?

109% = redline = engine limit/surge/stall checklist = pull back throttle

 

There just is not that much more you can get out of them engines past Amber Line.

Not without the risk of doing some major damage to them at N1 Redline.

Is that what you are looking for? You want to see if you can blow them appart?

Yeah maybe they did not simulate that part :-)

 

I looked into the 777 maintenance manual but found no helpfull further info.

You would need a GE manual which I dont have.

 

As far as I know you should never ever ever get close to Redline N1 even in alternate EEC mode. Unless that engine has a problem BEYOND the EEC being in alternate mode.

But like I said I have no data to prove me wrong or right. I dont know if it can do 103% or 105% or 107% with EEC off. And neither do you. So we can not say this is simulated correctly to the last bit or not.

No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

 

The N1 RPM limit is 110.5%. As part of the certification process for the GE90-115B engine, they were ran for 60 hours at N1, N2, AND EGT redline while developing 127,900 lbf. I don't call that "not much more", that's 10% more thrust than rated (115,300).

 

Which will be certainly very helpful in a MTOW + engine out + unexpected windshear situation even if it means that the engines will need a check by maintenance afterwards.

 

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From the FCOM

 

 

 

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 thrust lever positions. The EICAS

caution 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.

 

RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

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I dont have the PMDG FCOM with me but I am pretty sure there is no difference between that and my personal FCOM. Which clearly states that N1 and N2 limit protection (redline) is available also in Alternate mode. That means that you can get passed the amber line and if there is some sort of an additional engine problem (governor for example) which would result in RPM increasing to redline then the EEC will prevent this by commanding reduced fuel flow. So no...you can not go up to N1 red line.

 

I hope you dont mind, but I have no further info on this subject.

Maybe a GE engineer can pickup from

Now you have added some hypothetical "governor". That's certainly not in the docs. I really doubt PMDG looked at a GE engine document and said "Hmm, we'll just introduce this hypothetical "governor" into our EEC code that the FCOM documents don't mention".

 

The FCOM also says that ENG LIMIT PROT message will show up if the thrust lever position commands an N1 greater than the maximum rated thrust. Why did PMDG even bother programming that message in if there's no way a sim user can trigger it (without mashing F4/slamming throttles).

 

It is far more likely this is a bug instead of your hypothetical governor and that the EEC simulation programmer didn't consider that thrust overboost protection needs to be turned off instead of following the FMC calculated values.

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From the FCOM

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 thrust lever positions. The EICAS

caution 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.

RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

I know, that is what I have been saying the whole time. He is just not getting that there is a difference between THRUST LIMIT PROTECTION (a protection against too much force) and N1 LIMIT protection (a protection against too high RPM).

I dont know how else to explain it too him :-(

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RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

Whose point are you trying to make anyways?

 

My point is that it doesn't get anywhere close to redline, it's always 1-2% above amber line (and 8-9% below redline). Unless everyone else on this thread seems to get close to 110.5% N1.

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No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

 

The N1 RPM limit is 110.5%. As part of the certification process for the GE90-115B engine, they were ran for 60 hours at N1, N2, AND EGT redline while developing 127,900 lbf. I don't call that "not much more", that's 10% more thrust than rated (115,300).

 

Which will be certainly very helpful in a MTOW + engine out + unexpected windshear situation even if it means that the engines will need a check by maintenance afterwards.

I think it's you who don't understand. No protection does not mean that the scheduled N1 is not limited.  Full throttle could be scheduling 105% N1, or some other figure less than the red line. I don't know about the 777, but on the 747-400 (with FADEC engines) if you switch to ALTN mode and firewall the throttles the engines do not red line. They run at a higher N1, but not near the red limit.

 

Also did you not read my post earlier when I referred to what PMDG said about this.

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.

I read that as meaning the EEC is always limiting in their model, possibly because of FSX limitations. To be able to set 110.5% N1 with limits off, the throttle position for the EEC normal case would be somewhat reduced. It's all a compromise, you shoud not expect perfection everywhere.

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No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

.

Yes it does work like that. In Alternate mode EEC THRUST LIMIT protection is gone but you still have EEC N1 RPM limit protection!!!! Two different thing, that is what I have been trying to explain to you all the time.

 

Ok good N1 redline is 110.5%

Like I said I am looking at my own (my airlines) FCOM and we have the GE90-90B with max 109% N1.

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