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News: The latest PSX update (version 10.42 from 16 August 2018) is available at: http://aerowinx.com/board/index.php?topic=4191.0

Author Topic: ENG FAIL -- Inhibited on Ground?  (Read 6749 times)

Avi

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #40 on: Sun, 6 Mar 2016 02:41 »
I'm sorry but I don't understand what Peter's last test proof.
With Vr of 167 kts, speed of 159 kts is above V1. At this point even engine fire is only announced by EICAS message, not by a warning light or the bell sound.
Did anyone expect to get a Caution message (EICAS message, light and sound) at this point? I'm not surprised at all he didn't get it (I was if it was the other way around).

Cheers,
Avi Adin
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emerydc8

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #41 on: Sun, 6 Mar 2016 03:34 »
Hi Avi,

It is my understanding that we were only looking at the ENG FAIL EICAS -- not the master caution lights and aural indication. Those would be inhibited until VR + 20 seconds or 400' AGL, but the EICAS caution ENG FAIL would still appear on the EICAS as soon as you are airborne. 

Jon D.

Britjet

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #42 on: Sun, 6 Mar 2016 11:14 »
Indeed.
Peter

Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #43 on: Mon, 7 Mar 2016 20:45 »
My manuals also say "air mode".

N2 less than 50%
Oil pressure less than 10psi (GE only,* 25psi for RB211s)
Fuel control switch ON
GCB is open
Airplane in air mode

Perhaps the momentary loss of a generator put some part of the air-ground system into air mode? (although I can't imagine a sim simulating this)

Can you recall which engine failed?

I find the oil pressure logic strange. I thought a windmilling engine in flight would be able to keep some kind of oil pressure in the system (EDIT)* Another manual specifies a more sensible 70psi for the GE.

Rgds
JHW

These quoted, engine specific oil pressure figures for the ENG FAIL message agree with the respective red range on the EICAS.

25 on RR
10 on GE
etc.

It makes sense.

After a flame-out it will always drop into the red range.


Cheers,

|-|ardy


P.S.: As for the air mode: Could it be that the EIU, in this case, uses the same PSEU relay that it uses for the IDLE DISAGREE message (F23 ...)? If that relay fails on the ground, ENG FAIL can appear on the ground. Better than never.




« Last edit: Mon, 7 Mar 2016 21:55 by Hardy Heinlin »

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #44 on: Tue, 8 Mar 2016 00:47 »
Quote
After a flame-out it will always drop into the red range.

Thanks. I temporarily misplaced my oil pressure Vs rpm chart for the GE. After relocating it, I see 10 psi to 30psi is the normal pressure range for the engine at idle.



For the RB211, 25psi does seem to be a significant number. Quoting the Engine/Aiframe Engineering Training notes...

During rapid deceleration, Oil Pressure may drop below
25psi, this is permitted provided the pressure doesn’t drop
below 18psi and recovers to above 25psi in 5 minutes.


I guess I was (incorrectly) assuming that because a windmilling engine hydraulic pump produces sufficient pressure at high airspeeds, so might the oil pumps.

Rgds
JHW


Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #45 on: Tue, 8 Mar 2016 02:06 »
New logic is now implemented in 10.0.8 beta 6:

http://aerowinx.com/board/index.php?topic=3462.0


|-|

Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #46 on: Wed, 13 Jun 2018 19:20 »
Note: The above last post was from 2016. Now we're in 2018.

I just noticed in my GE model, when a flame-out occured, the oil pressure stays above the red range (above 10 psi) when the airspeed is above ca. 260 KIAS.

When above the red range, i.e. above 260 KIAS, the ENG FAIL message cannot occur. This consequence only affects the GE model with its GE specific oil pressure limit system.

In PSX version 10.0.8 I had set the following oil pressure minima for the ENG FAIL message as per certain maintenance documents:

GE : 10
PW : 70
RR : 25

Now I'm asking myself what I should do with that GE minimum to get ENG FAIL also at a higher KIAS:

1. Modify the ratio of N2 windmilling versus oil pressure so that it will drop into the red at any KIAS.
2. Use the amber limit instead of the red one.
3. Leave it as is and assume this effect also occurs on the real GE (but maybe not in the big sims).

I prefer #1.

Any opinions?


Regards,

|-|ardy


P.S.: If the GE at idle sets an oil pressure of up to 30 psi, and if 10 psi is truly the miminum for the GE's ENG FAIL message, then maybe it's intentional that the GE won't trigger the message? Maybe the designers don't consider a tempoary flame-out a serious engine failure? The oil pressure will go into the red when a severe FOD or compressor surge occurred.
« Last edit: Wed, 13 Jun 2018 19:49 by Hardy Heinlin »

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #47 on: Thu, 14 Jun 2018 03:30 »
Do we have any videos of any engine shutdown showing oil pressures? Perhaps we could get percentage oil pressure drop with decreasing N2 or N3?

Probably not the best idea comparing engines though. N3's may behave different from N2's.

Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #48 on: Thu, 14 Jun 2018 07:20 »
The parameter ratios in PSX are based on engine start observations (for each engine type). I think when shutting down, the RPM related oil pressure behaviour will not be much different.

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #49 on: Thu, 14 Jun 2018 08:42 »
I found a somewhat blurry video of shutdown on an RB211 (after an engine ground run).

  0:00 Idle pressure at engine shutdown was 64psi at 60%N3
~0.02 60psi at 47%N3
~0:03 50psi at 42%N3
~0:05 40psi at 35%N3
~0:07 30psi at 30%N3
~0:12 20psi at 22%N3
~0:27 10psi at 11%N3



Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #50 on: Thu, 14 Jun 2018 09:11 »
Thank you. The RB211 stuff is fine in PSX. The message problem only affects the GE model with its GE specific lower oil pressure limit system.

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #51 on: Thu, 14 Jun 2018 13:44 »
According to the AMM, at 55%N2, oil pressure anywhere between 10~30 psi is considered normal on the GE. I assume it's the upper normal value which is giving you problems.


Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #52 on: Thu, 14 Jun 2018 13:53 »
OK, thanks. I'll tune it further down below 10 for windmilling RPMs ...

Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #53 on: Fri, 15 Jun 2018 04:46 »
While we're at it ... I noticed an interesting side effect.

As we know, when the fuel control switch is moved to RUN, a 5 minute timer will start (indicated on Instructor > Analysis > Miscellaneous, top right corner, in seconds for each engine); when 5 minutes have passed, the EIU sets the engine-is-running status to TRUE, no matter whether or not the engine is physically running.

This status is used in various parts of the 744 systems where the logic checks whether the engine is running, e.g. for the ELEC GEN OFF message logic etc.

Is this 5 minute timer also used by maintenance on the ground to simulate the engine-is-running status for certain logic tests while the engine isn't physically running?

Or is it used for the system logic alone (not for maintenance tests) to latch the engine-is-running status once the engine has been physically started? The status can only be reset by switching the fuel control to CUTOFF.

I'm asking because ...

The engine-is-running status is set to TRUE when N2/N3 is above ca. 50% OR when the fuel control is in RUN for 5 minutes.

The RPM range around 50% (+/- 1%) is a critical range for some logical sequences and timings. E.g. when the IDG fails due to low RPM (ca. 50%), the ELEC GEN OFF message will only occur when the engine is running, and that is (physically) only the case when N2/N3 are above ca. 50%. To get rid of this dilemma, we have the 5 minute timer. This latches the eninge-is-running status until the fuel control is switched to CUTOFF. Thanks to this timer, all logical effects which indicate while-engine-is-running failures will operate correctly -- even if the engine has spooled down below 50% in the moment when the failure occurs.

This is fine. But ...

When a failure occurs before 5 minutes have passed, the trick won't work.

So my actual question is ...

Should the timer jump to its 5 minutes level as soon as N2/N3 are above 50%? Only the 5-minutes-passed status will latch the engine-is-running status. Once the engine is truly running, do we want to latch it immediately or only after 5 minutes?


Cheers,

|-|ardy

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #54 on: Fri, 15 Jun 2018 12:17 »
Quote
Is this 5 minute timer also used by maintenance on the ground to simulate the engine-is-running status for certain logic tests while the engine isn't physically running?

Perhaps the guys who work in major maintenance can answer this. I've not come across any specific checks which require the fuel control switches in RUN for 5 minutes. For line personnel, the message is just a side-effect of pulling CBs.

Quote
Should the timer jump to its 5 minutes level as soon as N2/N3 are above 50%?

The schematics simply show an OR gate for the engine running logic. Based on this, the timer should keep running, but I wouldn't bet my life on it  ;D

Hardy Heinlin

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #55 on: Fri, 15 Jun 2018 13:38 »
Any idea why they didn't implement an immediate latch instead of a delayed latch? I mean, they could also latch it after 2 seconds instead of 300.

May these 5 minutes relate to oil system stabilization?

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #56 on: Fri, 15 Jun 2018 16:17 »
Or engine at operating temperature in general. We are told not to firewall the thrust levers until 5 minutes have passed.

But you do get some odd systems with this 5 minute run timer:

Faults relating to GE 11th stage cooling (by air)
FLIGHT RCDR SYS Status message
Probe Heat messages (e.g. HEAT P/S CAPT)

Some messages are latched, some aren't.

jcomm

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #57 on: Fri, 15 Jun 2018 18:26 »
Or engine at operating temperature in general. We are told not to firewall the thrust levers until 5 minutes have passed.


Meaning that a takeoff shouldn't occur withing 5 minutes of the latest engine start ?

John H Watson

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #58 on: Sat, 16 Jun 2018 00:38 »
This applied to maintenance procedures (RB211). Our pilot procedures included the following:

Before Takeoff Procedures (CF6):
Engine oil temperature must be above the bottom of the temperature scale
Run the engine for at least 3 minutes
(During taxi) Use a thrust setting normally used for taxi operations

Before Takeoff Procedures (RB211)
When the engines have been shut down for more than 1.5 hours, run the engines for at least 5 minutes
When the engines have been shut down less than 1.5 hours, run the engines for at least 3 minutes.
(During taxi) Use a thrust setting normally used for taxi operations
Oil temperature must be above the lower amber band before takeoff.

jcomm

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Re: ENG FAIL -- Inhibited on Ground?
« Reply #59 on: Sat, 16 Jun 2018 23:52 »
Thx John !