ENG FAILURES

[Skybird]

Hi everyone!
I have questions regarding the ENG FAILURES in cruise on PSX.

First of all, the CON thrust is immediately selected as soon as the engine fails. I guess it should only come when EXE the ENG OUT page on the VNAV FMC...

Let's assume the aircraft is ABOVE the MAX ALT one engine out.
This means that the aircraft is too heavy to sustain the current altitude on the remaining 3 engines. A descent will be required:

- at the E/O Drift Down speed
- at the E/O LRC speed

depending on the conditions (delay, terrain... )

In PSX, the aircraft can easily stay above the one engine out MAX ALT on 3 engines which looks very strange to me.
Normally, when reaching the DD SPD, the R/D should approximate 300ft/min with max CON thrust on the remaining engines.
When the DD is executed (at E/O DD SPD), I noticed that even at high weights, the CON setting on the remaining engines is never at its green threshold value. I don't know if this is normal as I always believed that above the MAX ALT you always needed the max continuous thrust available on the remaining engines to decrease as much as possible your ROD until your DD level.
Is it also normal to have a HOLD indication with the VNAV SPD during the DD  :shock:
I would rather understand a THR as the CON thrust setting has to be maintained during the descent...

Can someone fix my "bugs" about this :lol:

[Britjet]

Hello Skybird,

Some interesting research there! It is good to see guys exploring the envelope with PSX!

Here is my explanation..
CON will annunciate immediately if the engine fails in the cruise. I has nothing to do with engine-out selection, which only dictates the speed in the FMC.

(By the way, if you have an engine failure after take off, CON will annunciate at V2+98 kts.)

With regard to the engine drift-down, I am not sure why you are having an issue with the aircraft maintaining altitude above MAX ALT - that is not my experience with PSX. I would be interested to see your situ, if you have it. It *does* take quite a while for the aircraft to decelerate and have to then descend - as much as 2-3 minutes sometimes.

Executing the D/D *will* cause the thrust to reduce to the E/O speed. This is a function of the autothrottle system and is inherent in the design. I admit it sounds a little strange, but if you want to maintain your higher altitude as long as possible, the technique is to wait for the speed to blled back to E/O DD speed  (which is always 10kts above Vman) with full CON thrust  and then EXECUTE. The Autothrottle will remain in CON, but start a gentle descent, as you now have a speed mode engaged.

it is important to select E/O DD, as you obviously realise, as if you select  the (much higher) LRC, which is alternative, the aircraft will descend more or less immediately!

So, not bugs, but a realistic PC-based simulation, I feel!

I hope that this helps,

Regards

Brit

[Hardy Heinlin]

Hi,

PSX models the logic that the real-world EIU/FMS uses, which -- if I'm not wrong -- works like this:

If in flight
and thrust mode is CRZ or CLB or CLB 1/2
and (
any engine's N2 (N3) is 10% below the value of the best engine
or any N2 (N3) is below 45%
)
then set CON.

(There is another function when in TO mode for the Vref+98 stuff.)

In fact, while all four engines are running, you can pull a single thrust lever by some degrees and get the CON trigger because of the 10% delta function.


As for the MAX ALT: These values are theoretical values. There is no "glass" at that altitude. The aircraft won't hit a roof and the path won't make a sharp knee. I think one should allow some flexibility around that point, especially since not every aircraft has exactly the same performance as the other (think of drag and FF corrections etc.).


Cheers,

|-|ardy

[Skybird]

Brit, Hardy, thanks for this interesting replies.

Pls note that when I was mentioning "bugs", I was talking about myself    I do trust a lot PSX as it was designed for years by Hardy with the help of engineers... But I like to understand things... and learn!!

Brit, what you say makes sense. However, in the Engine Inop CR/DD chapter of the FCTM, Boeing writes that "The FMC commands E/O LRC and sets the maximum CON thrust". Same in the FCOM, Boeing's sentence seems to be confusing by stating that the CON setting is coming after EXE the E/O FMC page.

The FMC computes and displays thrust limits for all modes. Selection can be done via the Thrust Limit Page (or the THR sw with VNAV or FLCH). So Hardy, you mean that there is an engine failure recognition system (through the N2) which will automatically set the rating to CON in those modes? Does that implies that the thrust levers will physically move to a higher thrust if needed, without any action on the FMC (which normally controls full-throttles operation)?

Brit, I do confirm that flying 3000ft above the E/O MAX ALT (so on 3 engines!) is possible with PSX. I don't know why, but I do not have any speed decay, even after 5 minutes.
W=335T FL340  E/O Max FL is 310
Of course, if you increase the weight, and the delta Alt, the speed WILL decay...
I do not understand your point about the DD SPD which should be 10 kts above VMAN... Well, I know that it should be not very far to VMAN :roll: , and approximately 15kts below the E/O LRC SPD... But here in PSX, my E/O DD SPD is 30kts above VMAN which looks to be a lot. Flying at .84 (CI of 80) in MNPS for example will impose me to accelerate to the Min Drag speed in case of engine failure... You see what I mean?

I also couldn't find the reason why PSX shows HOLD after an engine failure, while performing the DD, especially with high thrust settings (like 95 to 100%N1). Boeing describes the HOLD function as appearing after IDLE (or close to) in VNAV or FLCH modes.

When I perform engine failures on takeoff with PSX, my CON is not coming at Vref+98 as it should be. In VNAV, it seems it is coming when selecting flaps 5... :shock:  Otherwise in FLCH, it stays in take off thrust and is becoming CON when I press the THR switch (at Vref+98 basically) which is normal.

Just a last question: When I start PSX I can see version 10.0.0, also in Instructor "About/Quit". I did the update 10.0.2 last week. Is it still normal to see 10.0.0 in the windows I just mentioned?

Thank you very much for your replies.
I'm sure I will again learn something...

Regards
Steve

[Britjet]

Hi Steve

A lot of stuff there! If I may quote..

"Brit, what you say makes sense. However, in the Engine Inop CR/DD chapter of the FCTM, Boeing writes that "The FMC commands E/O LRC and sets the maximum CON thrust". Same in the FCOM, Boeing's sentence seems to be confusing by stating that the CON setting is coming after EXE the E/O FMC page."

- I know :-) Notwithstanding the text, the three different full-flight sims that I used did the throttle-back thing unless at high weight. In my (sim) experience the system just isn't clever enough to do what Boeing describes. We used to brief the trainees on exactly the points you mention, and then see the sim throttle back!
You just have to wait before you execute..

With regard to Vman - I know that Hardy has programmed the E/O DD speed at Vman +10, so if it is showing something different then I don't understand that. I will have a try..

I'm not sure why you are getting the CON at Flap 5. I will try it, but in my experience PSX do this correctly..

There is definitely something amiss with your update - if you have the latest you should be showing 10.0.2 (unless you have the betas, as well)

Cheers,

Could you post a situ?

Britjet

[Britjet]

Actually - if you have the original 10.0.0, that would probably explain quite a few things!!!
The D/D was changed in a Beta quite a long time ago and is incorporated in the latest updates.

Hope fully you can update OK to 10.0.2 - then give it a try..

Brit

[Skybird]

Hi Peter!
I found out that I was still using the old version iso having the new beta14 version active... Now, when I start PSX, I do have 10.0.2 showing! Uh... I'm definitely not into computers  :roll:
I have to say that the "handling" is now fantastic! It's a real pleasure to play with the FMC and AP features, in normal AND abnormal situations. Hardy is a real artist...

I understand more what you were trying to tell me as, now, PSX is running better  :lol:
Sorry if I made you worked on already solved issues...

Executing the D/D *will* cause the thrust to reduce to the E/O speed. This is a function of the autothrottle system and is inherent in the design. I admit it sounds a little strange, but if you want to maintain your higher altitude as long as possible, the technique is to wait for the speed to blled back to E/O DD speed (which is always 10kts above Vman) with full CON thrust and then EXECUTE. The Autothrottle will remain in CON, but start a gentle descent, as you now have a speed mode engaged.

I fully understand this, and yes, it sounds very strange. Thrust is available till CON, but the ATHR is reducing the power... what a non sense!
As you are very familiar with the PSX (and the 744) could you please help me with this procedure?

There are 2 ways to deal with this event:
A. ENG FAILURE = at this stage, all remaining eng go to CON setting
    1.On VNAV pge, prompt ENG OUT
    2.prompt E/O SPD LSK5L
    3.EXEC (VNAV ALT checked)
    4.All remaining thrust levers retard which is absolutely very strange (why not keep CON thrust setting?), and yep... the speed drops (trend vector appears, so it's quite rapid)
    5.Set the MAX ALT on the MCP
    6.When DD SPD reached, PRESS MCP ALT button
    7.THR / VNAV SPD checked - HOLD appears (Can't find it in Boeing doc). Depending on the weight, a shallow descend starts (300-500ft/min). All remaining engines are NOT at the CON thrust, which again is strange, considering the fact that if they would be, the aircraft would have a better Drift Down performance... and would stay longer at a higher altitude.

B. ENG FAILURE = at this stage, all remaining eng go to CON setting
    1.On VNAV pge, prompt ENG OUT
    2.prompt E/O SPD LSK5L
    3.Set the MAX ALT on the MCP (no press!!)
    4.EXEC (THR / VNAV SPD checked) All remaining thrust levers retard, speed drops, the aircraft keeps its flight level
    5.At the DD SPD - Thrust levers retard more (till idle?), HOLD appears, the aircraft "dives" (1800ft/min in my case)... why?

There is no difference between A or B except that the ALT is selected at a different moment. The VNAV system should work exactly at the same manner in both cases.
In B, at the DD SPD, I don't see the reason why PSX is giving such a high rate of descent with a so low N1... Have you tried this in a sim?

The FCTM (Chap4) "ENG INOP CR/Driftdown" does explain how to deal with this procedure: they describe the actions carried on case B which gives the "shallowest descent profile and level off at the highest possible engine out altitude".

For the rest I am very glad I have this Beta 14 update because all my issues are solved...

Thanks for your patience and great help.

Regards,
Steve

[Britjet]

Hi Steve

Boeing specifies various ways of dealing with the problem of engine-out in the cruise when above engine-out MAX ALT. The most useful is the one that delays descent.

If I look at your (B), I see a couple of problems..
1) You say you (5) MAX ALT in the MCP - I presume that is the engine-out MAX ALT? If not it won't work.
2) More importantly, you say in (6) Press the MCP ALT button. That is not correct. If you press the button you are effectively saying - "go down to the altitude" to the FMC, and you will have thrown away your carefully-planned low descent rate. It will go into HOLD because you have effectively now told it you want to do a cruise descent and nothing more..
So, in method (A) - don't press the button!

Let me give you a sequence for that..
1) Engine fails - Thrust goes to CON automatically.
2) Select "Engine Out" option on the VNAV CRZ page. It will display 3 eng DD MAX ALT. Set that in the MCP (or lower).
3) Select E/O SPD (don't execute).
4) The engines stay in CON, airspeed reduces..
5) As speed reaches E/O speed bug, EXECUTE. The aircraft should now "drift-down" with CON thrust.

Try that..

With regard to (B), it looks to me as though you might have achieved VNAV ALT?
In which case the aircraft will never descend, a dangerous situation. Did you stall it? Which might account for the ROD? I can't be sure..

You sound like you might be a rw pilot? In which case - method (A) might make more sense for you, but please follow company procedures!

I will try and find time to fly out a cruise DD..

Rgds,

Brit.

[IefCooreman]

As far as I'm aware, the pushing of the altitude selector on the MCP completely governs how the engines will react when you execute the driftdown page. If you don't push it and execute the D/D, engines accelerate to CON unless current altitude can be maintained. If you do push the altitude selector, engines react as for a normal VNAV descent.

I do admit my only "seen-it" knowledge is twins, and I know from my collegues that the 744 is a different beast when it comes to engine out. They tell me in many cases, a driftdown is not even required...

However, if you set the altitude on the mcp lower than the current, and you execute the engine out page, the rating changes to CON. The initial target speed might be company specific. For the majority of the twins this is usually driftdown speed, since we are much more performance limited. The engines will accelerate to CON thrust, and during the deceleration phase the rate of descent is really minimal (though present... I would say between 0 and 300fpm). If you now push the altitude selector, you force the VNAV into a descent and the engines will react as for a normal VNAV profile.

Practical real-life example use that might make things clear:
Flying a track over the atlantic you experience an engine failure. In MNPS airspace you have a special offset procedure where you turn to a 15NM offset parallel track (either direction is possible depending on your alternate). During this turn to the parallel track you have to minimize rate of descent.
1) select VNAV D/D page
2) select target D/D altitude on MCP alt selector (do NOT push)
3) execute VNAV D/D
4) remaining engines go to TOGA, speed SLOWLY drops to target D/D speed, aircraft maintains fairly level flight with possible shallow descent
5) once established on the 15NM track select your diversion speed on D/D page (could be LRC ie). If you execute now, the engines will remain in CON, however the nose will pitch down to allow the aircraft to accelerate but still with shallow descent
6) re-check target D/D altitude (higher speed will result in lower max altitude)
7) set your target FL for the diversion on the MCP altitude selector (MNPS procedures require you to descend below the tracks as soon as possible) and PUSH the altitude selector. The engines now rollback to do a normal VNAV descent at the requested target speed.

(ps: this procedure assumes no ATC clearance to stay higher which might be possible. But normally - once established on the 15NM offset - you "glide" down to below the track levels)

[Skybird]

Hi everyone!

Hardy, sorry to come back so late to this subject, but I needed time to get more info.

PSX models the logic that the real-world EIU/FMS uses, which -- if I'm not wrong -- works like this:

If in flight
and thrust mode is CRZ or CLB or CLB 1/2
and (
any engine's N2 (N3) is 10% below the value of the best engine
or any N2 (N3) is below 45%
)
then set CON.

(There is another function when in TO mode for the Vref+98 stuff.)

I spoke with a Boeing instructor, a few B744 company instructors/examiners, and a rated 744&777 chief pilot. None of them are aware of this feature, and don't even remember having seen it in the "options" that could be chosen from the manufacturer.

So I have been in a B744 simulator and carried out an inflight engine failure above the ONE ENG OUT MAX ALT. The CON setting is only coming when pressing the Eng Out VNAV page, as described in all Boeing manuals. I waited that the speed reached the min man yellow band before executing, just to see if CON could come later... But no...

Now, here is what I found out in the Flight Crew Operating Manual (Flight Management, Navigation section), about the Drift Down Execution procedures. There are 3 ways of dealing with the DD execution. The 3rd condition explains that, after having set a lower altitude (Below the E/O MAX) in the MCP Alt window, and after having pushed the Alt selector, the aircraft descends in a normal VNAV cruise descent at 4 economy cruise speed. The thrust limit is CLB/CRZ and the autothrottle maintains cruise speed. Executing the ENG OUT on the FMC while descent is established, sets the speed to E/O LRC SPD AND the CON thrust limit.

This invalidates the theory you mentioned above, at least for climb, cruise and descent phases. However, for the takeoff phase, these conditions are valid (except for the CRZ thrust mode that you cannot have during that phase). At Vref+98, the thrust is automatically reduced from the selected takeoff to CON setting. If the engine failure occurs above the thrust reduction point, Boeing says that the current climb thrust is maintained.
Consequently, again, you cannot have CON automatically when an engine is failed without having executed the FMC page.

The only "engine failure sensed" condition I know is:
-N2 less than 45%, or invalid data for about 1 second
-More than 10% N2 difference with other engines

This detection is used as one of the inputs to the FMC during takeoff phase for the VNAV function...
VNAV ACTIVE (so in flight) and Engine failure sensed and below engine out acceleration height and below the thrust reduction point and airplane at Vref+98 = CON will set automatically


During an engine out procedure, PSX is reducing a lot the thrust setting (as I already mentioned in previous post) as soon as ENG OUT is selected. In the simulator, the thrust remains in CON trying to use as much power as possible to minimize the descent. Also, the maximum R/D that can be seen is 1250 ft/min. During the LRC procedure, when your speed is below the E/O LRC SPD, the aircraft is trying to recover its FMC speed with 1250ft/min with full CON thrust.

The HOLD feature occurs during the LRC descent which I completely forget. PSX made me learn something, which is good! This is why I bought it honestly... To use it as a powerful learning and revising tool   And until now, I'm very impressed...

I don't know if this is relevant or not, Hardy, but I compared the PSX data with the real aircraft FMC data. I know there are a lot of parameters involved...

First of all, the Normal Cruise Mach number (let's say for a fixed Cost Index of 80) is way too high. Here are some numbers
FL 330 - W 344T TAT within 1°, SAT within 3° - CI 80 ECON SPD
M = .874(PSX) .844(real)
IAS = 315(PSX) 303(real)
Lo Spd = 265(PSX) 278(real)
Hi Spd = 325(PSX) 329(real)

For the engine out, PSX is showing the same MAX ALT for the LRC SPD and the E/O DD SPD, which denies the definition of Max Range (Min drag) and Long Range options offered by the FMC. The level off altitude following the E/O DD SPD must always be higher than the LRC procedure... The LRC Mach in PSX is showing .879 vs .852 in real...
You might not have designed PSX to display the exact performance of the 744, which I fully understand, but what I am trying to say here is that the first time I saw the PFD, something "unusual" caught my eyes... The speed was too close to the High speed buffet, and the Mach number was too high (with a cost index of 80)

[Skybird]

As far as I'm aware, the pushing of the altitude selector on the MCP completely governs how the engines will react when you execute the driftdown page. If you don't push it and execute the D/D, engines accelerate to CON unless current altitude can be maintained. If you do push the altitude selector, engines react as for a normal VNAV descent.

Hi IefCoorman,

This is not always true...

There are generally four reasons to press the altitude selector after an MCP selected altitude change:

1.The aircraft is in VNAV ALT or VNAV PATH and the PF wishes to initiate a climb/descent
2.The aircraft is in VNAV SPD (climb or descent) or VNAV PATH (descent) and the PF wishes to delete the next RTE LEGS page speed/altitude restriction (which is between the aircraft and the MCP selected Altitude Selector)
3.The aircraft is NOT in VNAV, but the PF wants to delete the next RTE LEGS page speed/altitude restriction
4.The pilot needs to increase the Cruise Altitude in the FMC Cruise Page, based on the MCP Altitude Selector

In case 4. the aircraft doesn't initiate descent or climb... and you pushed the alt selector...

[Hardy Heinlin]

Thanks, Steve.

OK, I'll try to restrict the CON logic to the take-off phase only.

Re econ speeds: What tailwind did you use for these comparisons?

And, generally ... which engine model? The cost index in PSX is based on GE data using minimum cruise speed tables for CI 0, and high speed tables for CI 9999, with LRC tables providing data for CI 200 plus dynamic wind additives.


Regards,

|-|ardy

[Skybird]

Let me give you a sequence for that..
1) Engine fails - Thrust goes to CON automatically.
2) Select "Engine Out" option on the VNAV CRZ page. It will display 3 eng DD MAX ALT. Set that in the MCP (or lower).
3) Select E/O SPD (don't execute).
4) The engines stay in CON, airspeed reduces..
5) As speed reaches E/O speed bug, EXECUTE. The aircraft should now "drift-down" with CON thrust.

Try that..

With regard to (B), it looks to me as though you might have achieved VNAV ALT?
In which case the aircraft will never descend, a dangerous situation. Did you stall it? Which might account for the ROD? I can't be sure..

You sound like you might be a rw pilot? In which case - method (A) might make more sense for you, but please follow company procedures!

Helloo Brit,

Thanx for this sequence that I do know.
Many companies are now sticking to Boeing procedures, which means that their manuals are the official bible fully approved by the respective CAA. If I mentioned 2 methods (in fact there are 3 of them!) it is because they are black on white published by the manufacturer. In (B) I had VNAV ALT which is what Boeing wants in this particular case. I didn't stall it as pushing the alt button when on speed is the official procedure. It could be a dangerous situation if you forget to push the selector, but flying manually with no autothrottle during approach can also lead to a dangerous situation if your speed drops below your bug!! The concept of a dangerous situation might be subjective here...

In Boeing doc, the FCTM describes the way to perform the ENG OUT driftdown. And the FCOM explains the 3 conditions to execute a driftdown with the FMC.

Talking about stall... PSX does not reproduce the stall protection of the aircraft. At low speed, at half way into the yellow band, autothrottle in ARM with NO mode active (blank window), the SPD mode should engage automatically...

Regards,
Steve

[Hardy Heinlin]

Talking about stall... PSX does not reproduce the stall protection of the aircraft. At low speed, at half way into the yellow band, autothrottle in ARM with NO mode active (blank window), the SPD mode should engage automatically...

Never heard of that. Is that a new feature?

What do you mean by "blank window"? Blank MCP window or blank speed mode on FMA?

[Skybird]

Hardy,

No tailwind. In PSX I had 65kts HW component, on real flight I had 32kts HW component.
For PSX I used GE B1F
Real aircraft fitted with GE B5F
Performance wise, Boeing makes no difference with both engines config. That's what I see in the Supplementary Data Document.


Stall protection is provided depending on the modes engaged and aircraft situation.
If the FMA left (thrust) window is blank, but the A/THR sw is in ARM, the SPD mode will automatically engage if your speed drops below the min man speed (yellow band), and depending on the position of your speed bug the A/TH might deliver max thrust. This is independent of the AP (meaning auto or manual flight)

If the A/THR is OFF, the stall protection is only available through the following pitch modes: VNAV SPD, FLCH SPD, TOGA. The AP brings the aircraft nose down... I assume that if AP is off, you should see the FD pitch down command while flying manually...

[Skybird]

A new feature???    Nooo... I saw it somewhere in the books.
There is also a high speed protection...

[cagarini]

I thought this only applied to the post 777 models ?  Never saw it in mentioned for the 744 ?

[Skybird]

See the "Flight Envelope Protection" chapter in Automatic Flight section  

[Hardy Heinlin]

A new feature???    Nooo... I saw it somewhere in the books.

When did you start your 744 type rating? When I say "new" I refer to years, if not decades :-)

Or are we now talking about the 747-8?


I just looked at one randomly selected manual from 2000; under
"Flight Envelope Protection" there is this note:

"With the autothrottle active, speed protection is normally available for all operations except V/S pitch mode."

It doesn't mention anything with A/T ARMED and blank FMA and automatic SPD mode engagement. This would also need some essential explanations for the flare, to avoid A/T engagement in case you are unusually slow shortly before touchdown.

[Skybird]

Do you always ask the good questions?? The ones nobody expect, and more specifically the ones that do not have any answer in the books??



This protection applies to the B744.

The low speed protection acts at [Min MAN Speed - 8kts]

It engages the SPD mode of the A/THR in the following conditions:
-A/THR in ARM and fully serviceable (Active or not)
-Above 100ft Gnd for Approach / Above 400ft Gnd after Takeoff
-The AFDS vertical mode FLCH SPD, VNAV SPD, TOGA are not the active modes

This provides an answer to your flare question.
But anyway, Boeing procedures allows a maximum of 10kts below your Vref during flare, at which you must touchdown (if I remember well).
At that limit, you're still above the low speed protection threshold