Dual Eng Fail simulation

[spetsnaz26 0]

Out of impulse I decided to fly a deadstick landing on the 777. In most aspects the airplane systems responded in an expected way, but I did notice details that are not quite what I expected. Hope the technical types on this forum would like to discuss a little bit about this particular aspect of the simulation.

 

I know by reading other posts here that some supporters are quite easily angered. So let’s start by stating this is by no means a challenge to PMDG's authenticity, since I have no idea how a real 777 will respond either. I read through the hydraulic, air, electrical, and flight control part of the SD in FCOM, and yes I also read through the entire Introduction manual. There’s not enough detail in the SD to explain what I saw.

 

I simulated 'dual eng fail' by moving both fuel cut off switches to off position.

 

problem 1: load shedding:

Initially, power was removed from FO's displays but soon is restored by the APU, which started automatically after loss of both main AC power sources. This matches what I read in the FCOM. To give myself a bit more challenge, I shut off the APU generator. A few moments later amidst hectic manuvering to line up with the runway, I found that power somehow is restored again to all the displays, against all the (man-made) odds!

 

On a different sortie FO’s displays were restored as soon as I moved the flap lever out of clean detent. Whether this is load shedding based on flap position I have no idea.

 

Another odd thing is that the MCP seems to be of a lower priority than FO’s displays, which is counter-intuitive…Setting airspeed/altitude/heading targets should be quite an essential and basic safety feature especially in a high workload scenario. Does this reflect the real thing?

 

 

Problem2: power source to the center hydraulic system

I understand RAT provides power to the center system when deployed. But at various points I found that either C1 or C2 ADP were powering the system as well, even after I switched off APU bleed as well as the pumps themselves!

 

 I tried shutting off APU bleed as well the two air demand pumps:

 

Now this is…a bit strange…Who’s powering Air C2, especially when C2 itself is commanded off? I also once saw both ADPs with green flowlines when in fact both were commanded off.

 

This continued as I slowed down to land. At some point I guess the RAT will have to drop out because the airflow feeding it is simply too weak. I ended up on the beach of Dubai. When I checked my systems I raised my eyebrow to the following:

 

 

 

 

Although the RAT did drop out at some point, the air demand pumps continued to work…and I was able to command surface movement after a complete stop.

I guess in an emergency like this, APU will ‘force’ feed the ADPs and simply bypass what’s happening on the overhead panel? I will try simulate a simultaneous APU failure or no-fuel condition to see how the system responds.

 

Minor problem 3:

HYD PRESS SYS L+C+R appeared once inflight, which is scary. What is the threshold of low pressure? Why did I still have flight controls?

 

Minor problem 4:

Flight control never dropped out of Normal Law, although only a portion of the surfaces were available. FCOM doesn’t specify conditions of mode changes, so I have no idea how this is supposed to work in real life.

 

Minor problem 5:

Once I saw the RAT animation to be static, although I was flying at 240kt, and the characteristic chainsaw sound is heard in external view:

 

 

Minor problem 6:

About alternate gear and flaps. I was able to extend flaps to 20, which is consistent with what the QRH says. But the flaps seemed only to start moving when I moved the normal flap lever to flap 20 detent. After reading FCOM, I got the impression that for electrical alternate to work, I only have to rotate the alternate flap switch to ‘EXT’ after arming it, right? This could be my illusion though, because I probably was flying too fast.

 

When the flaps did start to move, they seem to be moving pretty fast for “extremely” slow flaps! Coupled with the flap lever thing,,,could this be another quirk I don’t know (like some component of the hydraulic system is secretly assisting) or what?

 

The QRH says for alternate extension to work, I have to put the gear lever down, then hold the alternate extension switch down until the gear starts to move.

 

 

The FCOM on the other hand says gear lever has no bearing on alternate extension…In game, I could momentarily put the switch down but could not hold it…so what’s going on…

 

 

[3-2-1-Now 126]

Well that is rather interesting. X indicates FAILURE, so if the system was overriding the panel selection I'd expect to see the commanded position shown, not a failure. Not sure what the symbol for position disagree is on the synoptic - not dug that deep yet (still having too much fun flying it!!!).

 

Regarding FBW mode - unless electrical power is lost to some or all PFCs, as far as I'm aware it will remain in NORMAL mode.

 

Best regards,

Robin.

[tcas_climb 45]

Remember also the RAT not only provides hydraulic power but it provides some electrical power as well, and it will load shed if the demand on it is too great

[spetsnaz26 0]

Well that is rather interesting. X indicates FAILURE, so if the system was overriding the panel selection I'd expect to see the commanded position shown, not a failure. Not sure what the symbol for position disagree is on the synoptic - not dug that deep yet (still having too much fun flying it!!!).

 

Regarding FBW mode - unless electrical power is lost to some or all PFCs, as far as I'm aware it will remain in NORMAL mode.

 

Best regards,

Robin.

 

Robin, FCOM says amber box with a X should mean failed pump. If something disagrees, it should be amber as well. That's why it's so puzzling. Also, I found that when the APU kicks in in response to loss of both AC busses, the APU switch on the overhead stays in the 'off' position. This is a disagree and I would certainly like the rotary switch to spring to On position. Staying in OFF means I can't switch off the APU if I want to for whatever reason...

 

I noticed that all flight control electronics are powered, which is reassuring. But on Airbus at least, loss of surfaces/actuation/electricity is sufficient to drop to Alternate Law. How can 777 sustain Normal Law handling qualities with only a measly furry rat?

 

I guess PMDG has built up so much 'pent up' expectation, that we are now discussing things that are unthinkable for other flight sim software.

Remember also the RAT not only provides hydraulic power but it provides some electrical power as well, and it will load shed if the demand on it is too great

That's right, although the design of 777 electrical synoptic page didn't help because only AC is shown and there is no evidence on that page that RAT is providing juice as well.

 

I understand the electrical load management system is controlling the shedding, but why would MCP has a lower priority than the FO's displays? MCP shouldn;t draw nearly as much power as two D-size displays. Also, I question, assuming PMDG has simulated everything correctly, the design feature that will lead to FO  only having his display intermittently and rather unpredictably. 

[Jetstream96 20]

I understand the electrical load management system is controlling the shedding, but why would MCP has a lower priority than the FO's displays? MCP shouldn;t draw nearly as much power as two D-size displays. Also, I question, assuming PMDG has simulated everything correctly, the design feature that will lead to FO  only having his display intermittently and rather unpredictably. 

 

I think it's reasonable. In that situation, you won't use MCP at all. That may be the reason.

[willywonka 36]

 

 

Also, I found that when the APU kicks in in response to loss of both AC busses, the APU switch on the overhead stays in the 'off' position. This is a disagree and I would certainly like the rotary switch to spring to On position. Staying in OFF means I can't switch off the APU if I want to for whatever reason...
 

Well, for just this part alone, this is correct to the real plane. When the APU kicks in automatically it will not move the overhead switch. To shut down the auto APU you'll have to move the switch from OFF to ON to OFF.

[spetsnaz26 0]

Well, for just this part alone, this is correct to the real plane. When the APU kicks in automatically it will not move the overhead switch. To shut down the auto APU you'll have to move the switch from OFF to ON to OFF.

okay, that's what I suspect as well. thanks.

I think it's reasonable. In that situation, you won't use MCP at all. That may be the reason.

Well, my opinion differs in that I consider manually setting airspeed/altitude/heading targets to be an essential feature, for manual flight.  

[tjh87 9]

When the MCP was off, did the Heading Bug and Altitude Bug do anything on the displays? If so, then it might make some sense. Autopilot would probably not be engaged for various reasons, so the MCP displays are disabled, but the dials may still change info on the PFD and ND in regards to altitude and directional guidance. I am not saying in the real aircraft they do, that is my guess if the MCP shutting down is indeed normal.

 

And what you provided was very detailed and thorough. If someone get's angry at what you said, they are too thick skulled to see that you are trying to advance your knowledge, the forum knowledge, and bugs that might be present. I hope someone from the dev team pops in, because this is pretty interesting.

 

-Tom H

[spetsnaz26 0]

When the MCP was off, did the Heading Bug and Altitude Bug do anything on the displays? If so, then it might make some sense. Autopilot would probably not be engaged for various reasons, so the MCP displays are disabled, but the dials may still change info on the PFD and ND in regards to altitude and directional guidance. I am not saying in the real aircraft they do, that is my guess if the MCP shutting down is indeed normal.

 

And what you provided was very detailed and thorough. If someone get's angry at what you said, they are too thick skulled to see that you are trying to advance your knowledge, the forum knowledge, and bugs that might be present. I hope someone from the dev team pops in, because this is pretty interesting.

 

-Tom H

 

Tom, I thought about the same and found that the MCP is completely dead because the knobs have no effect on targets displayed on PFD or ND. I guess one either sheds the entire MCP or none at all.

 

The control law not degrading to secondary law, or even direct...is a bit strange to my Airbus accustomed mind. With that amount of surfaces lost, and the rest operating at a lower hydraulic flow-rate cap, how can Normal law still be sustained? If this is a realistic representation then Boeing really does have a very resilient flight control architecture.

[3-2-1-Now 126]

Robin, FCOM says amber box with a X should mean failed pump. If something disagrees, it should be amber as well. That's why it's so puzzling. Also, I found that when the APU kicks in in response to loss of both AC busses, the APU switch on the overhead stays in the 'off' position. This is a disagree and I would certainly like the rotary switch to spring to On position. Staying in OFF means I can't switch off the APU if I want to for whatever reason...

 

I noticed that all flight control electronics are powered, which is reassuring. But on Airbus at least, loss of surfaces/actuation/electricity is sufficient to drop to Alternate Law. How can 777 sustain Normal Law handling qualities with only a measly furry rat?

 

I guess PMDG has built up so much 'pent up' expectation, that we are now discussing things that are unthinkable for other flight sim software.

That's right, although the design of 777 electrical synoptic page didn't help because only AC is shown and there is no evidence on that page that RAT is providing juice as well.

 

I understand the electrical load management system is controlling the shedding, but why would MCP has a lower priority than the FO's displays? MCP shouldn;t draw nearly as much power as two D-size displays. Also, I question, assuming PMDG has simulated everything correctly, the design feature that will lead to FO  only having his display intermittently and rather unpredictably. 

 

Ahh yes... amber box. Not dissimilar to Airbus there, either. Hmmm....

 

Looking in the QRH, on dual engine failure, PITOT HEAT L+C+R is lost, and system should degrade to SECONDARY mode. LIke Airbus, this means protections are lost, and the aircraft must be flown conventionally. Check QRH 9.10.

 

Best regards,

Robin.

[spetsnaz26 0]

Ahh yes... amber box. Not dissimilar to Airbus there, either. Hmmm....

 

Looking in the QRH, on dual engine failure, PITOT HEAT L+C+R is lost, and system should degrade to SECONDARY mode. LIke Airbus, this means protections are lost, and the aircraft must be flown conventionally. Check QRH 9.10.

 

Best regards,

Robin.

I flew again with fuel quantity set to zero. This time there's no ADP, but flight control stayed in Normal Mode. "Flight Control" message was shown to indicate that some surfaces are unavailable. I guess the boeing control law and flight control architecture are simply very different.

 

Also, you mentioned Pitot Heat lost. Reading QRH dual eng fail checklist it does suggest that this message will appear as a result of loss of both engines. If all probe heating is off, then air data input to FCEs cannot possibly be trusted for control law computation. How is Normal Law still sustained?

[777simmer 117]

Out of impulse I decided to fly a deadstick landing on the 777.

Interesting excercise but...

 

Of all the failiures PMDG has modelled....it dont see Dual Engine Failure in the list (see guide)

 

Then....you are now getting in the territory of multiple (unrelated) failures which is not covered by Boeing even.

Like in this case it is assumed that at least one engine WILL restart.

 

Also...the synoptic diagrams are not te be used for trouble shooting.

That is a bit of a laim excuse as clearly there are some things in your pics that dont add up, but it is the truth non the less.

Synoptics are only for info.

Descisions are based on EICAS massages, not on what the synoptics shows.

Its not made for that and can indicate things that are not correct.

 

And finally, we will never know (unless we get a team of 777 engineers in here) what the airplane realy does in a case like this. Even in the full flight sim we sometimes sit there and ask ourselves...."was that something that realy happens like that or is that a simulator snag?" (that does happen yes)

 

I have been flying the 777 for more then 10years and I can not answere all those questions you have.

 

So it is a nice excercise, but I dont know how indepth the PMDG777 is or where it stops.

(I mean that, not sarcastic!)

 

Maybe someone from PMDG can fill us in here?

[spetsnaz26 0]

 

 

multiple (unrelated) failures which is not covered by Boeing even.

:lol: That's right, man. Reading Boeing's Dual Eng Fail checklist I got the impression that they assume at least one engine is restarted before reaching the scene of the crash. Airbus, however, provides some guidelines for what to do if relight is unsuccessful. You see, Boeing claims that its RAT can work across the envelope, while Airbus RAT has a minimum speed of 140kt. I guess it comes down to manufacturer philosophy, and intimidation capability when dealing with the FAA. 

 

 

 

the synoptic diagrams are not te be used for trouble shooting.

Agree. EICAS directs the checklist, and the synoptics are mainly for situational awareness. Software are generally designed to a lower specification than EICAS, too, hence the scope for misleading indication, although in this case I'm inclined to attribute the weird things I saw to limitation of the simulation. 

 

 

 

Even in the full flight sim we sometimes sit there and ask ourselves....

Training simulators and industrial engineering simulators are designed to different purposes. I trust that Boeing's in-house engineering rigs will have high-fidelity real-time system modeling that they could play with this sort of thing with reasonable confidence. you are right, simulations are always limited by model boundary conditions and the assumptions behind, that's why even in the 777 project Boeing still ran a compact flight test campaign, rather than carrying out all system tests on simulated platforms.

 

 

I have been flying the 777 for more then 10years and I can not answere all those questions you have.

:lol: Good for you man, I on the other hand have been confined to desktop simulation and academic studies because of lousy eyesight...By the way though, how does the alternate flap thing work on a real 777? I just tried a sortie with fuel set to zero, and found that the flaps refused to move with the switch armed and moved to 'EXT'...placard maybe?

[MKULTRA44 0]

I might be misinterpreting this, but my understanding was that the flight control laws relate only to the function of the flight computers which take pilot input and translate into physical movement of the flight controls. In your case, provided all computers stayed online, the law shouldn't change because despite the fact that the computers have less toys to play with, they are still functioning correctly. If one were to be taken offline, then a change in law would be expected. I'm just guessing here, not an expert by any means.

[777simmer 117]

:Good for you man, I on the other hand have been confined to desktop simulation and academic studies because of lousy eyesight...By the way though, how does the alternate flap thing work on a real 777? I just tried a sortie with fuel set to zero, and found that the flaps refused to move with the switch armed and moved to 'EXT'...placard maybe?

Hey, if I would have studied something proper, I maybe would not have to worry about downsizing and loosing my job constantly. Or about keeping the job under worse and worse conditions!

 

Simulation has come a long way.

I find it incredible what FSX and PMDG can do.

The result is that many guys/girls around here know what I know about the 777, some more (and some that think they know it all ofcourse haha), quite amazing!

 

I did not quite understand your question about alternate flap extention.