Hi,

 

Departing the Maldives on the way back to Dubai,  APU is inop & the right engine has a minor fault 'BLEED PRSOV R'.    

 

The Mel says it is ok to depart, however I need to reduce my RTOW due to the right pack being inop.   TOPCAT won't provide this data & I only have Airbus data.

 

Any 777 drivers that know what the weight reduction is?  I am going to try and get hold of some software in the next week or so.

 

Cheers 

Did we get a MEL with the PMDG documents?

 

According my MEL (777-200) you require the APU running for T.O. and Lndg with that status message.

Otherwise dispatch is not required!

 

If you get the APU working again, for the 777-200 with GE90-90B the weight reduction can be up to 9389kg.

At MLE and standard atmospheric conditions, no wind, it results in a reduced TOW by 6468KG.

 

If you do a PACKs OFF take off however, then you only have to reduce the TOW by 907KG.

 

But again, different 777 with different engines.

Hey Rob,

 

No MEL with PMDG I have access to AFM,FCOM,FCTM, MEL etc etc for a 777 operator out here.  Thanks for the info.

 

Regarding your company's MEL, so you cannot fly? do they not just limit your flight level?  

 

One last question, in my case the left engine was only supplying the left pack, shouldn't the engine be capable of supplying both packs?

 

Cheers

We are talking about the same thing I hope?

Bleed PRSOV R - STATUS message.

 

Without the APU and with that message we can not fly.

 

No FL restriction for us though.

Once again the different 777 types and operater options seem to make quite a difference behind the scene!

 

- The Associated Engine Bleed Air switch must be off.

- The APU is turned on during T.O. and Landing to power center system hydraulic demand pumps. L and R ISLN switch must be off for T.O and Lndg

- after flaps retracted, L and R ISLN swtich on and APU as required (off).

 

After T.O. you can turn the APU off because as you said, one engine can supply both packs. But bleed isolation system must be in AUTO mode for that.

 

The question is ofcourse how far PMDG has gone with its simulation?

Once again thank you for the detailed reply.  I am going to fire up the sim later and retest this again, left engine was definitely only supplying one pack (Bleed isolation was in Auto)  

what section is that under? i cant seem to find it in the MMEL.

36-11-01 in mine.

Thanks found it, i was looking under bleed air.

Forgive my plebian status, but why would this lead to a reduced RTOW?

 

My own mental processing is as follows:

If a pack is out, then less air is diverted from going out the back.

If more air is going out the back, then there's more thrust available to move the mass.

If there's more thrust moving the mass, then I can move more mass.

If I can move more mass, I should have a higher RTOW.

 

I'm sure there's a gap in that logic, though, because the actuality is that RTOW is reduced.  I'm just struggling to find where that gap is to close it...

Hey Kyle,  

 

Good explanation below, They are not my words.  

 

In the pack inoperative dispatch, the functioning pack maintains a high flow mode to compensate for the inoperative pack. The Fan Air Modulation Valve will also open fully on the engine supplying bleed, because the single pack operation in high flow mode requires cooler input bleed air. The operation of one pack in high flow mode therefore requires that the EPR on that engine be further reduced (relative to normal pack flow) to maintain EGT margin at the higher fan and core bleed level. Because the thrust management system will not permit any significant thrust asymmetry to be set, both engines will be throttled back to the lower level.

The net effect is that both engines are producing less thrust in the Pack Inoperative dispatch even though only one is supplying bleed air, at a higher rate, to supply the single operating pack. Also, after the assumed engine failure, the operating engine maintains the lower EPR value initially set, so the thrust in the one pack inoperative case is lower throughout the takeoff manoeuvre.

I actually had dispatched under this item before. Since 777sim had already answered the question. So I would like to share my little experience here.

 

As to flt level restriction, it will be FL220 or below if you lose the bleed air from the L engine in flight. Because APU bleed air valve will close above FL220, hence for the APU to be able to supply bleed air for the packs to maintain cabin pressurization we will need to descend to FL220 or below.

 

There's small " NOTE: " below the dispatch criteria saying the airplane must also be dispatched under MEL 73-21-01. Which is the Engine idle selection system.

 

I am not sure if PMDG model this, in real life, what MEL 73-21-01 implies is the ASCPC will command a higher N1 on the L eng to compensate for the increased bleed air demand in flight when R bleed air is not available ( higher engine speed for higher bleed air pressure ). As a result on descend towards the destination, the L eng will have a higher IDLE thrust than the R eng for above the reason, and the EICAS msg "Idle disagree" will come up when the thrust first goes to idle. And because of the higher idle thrust generated by the L eng, speed brake had to be used to drag airplane down on a normal Desend path. The problem can further complicate if ATC cut you short on the arrival, making it even harder to get down and slow down at the same time.

 

This is how a MEL item can affect on normal / nor normal operation. This is all very interesting stuff.

 

Happy flying everyone

Rob, i will assume that you can work around this reduced takeoff weight limit by just doing an unpressurized takeoff if you absolutely needed to? No packs running = even more mass.

Forgive my plebian status, but why would this lead to a reduced RTOW?

 

My own mental processing is as follows:

If a pack is out, then less air is diverted from going out the back.

If more air is going out the back, then there's more thrust available to move the mass.

If there's more thrust moving the mass, then I can move more mass.

If I can move more mass, I should have a higher RTOW.

 

I'm sure there's a gap in that logic, though, because the actuality is that RTOW is reduced. I'm just struggling to find where that gap is to close it...

We dont have a broken pack in this example.

 

PRSOV - Pressure Regulating and Shut Off Valve.

So you are missing the bleed air from the right engine and now the left engine has to supply air to both packs.

And thus it has LESS thrust available.

 

I guess the EEC will reduce the thrust on the other engine automatically to prevent assymetric T.O. thrust. So you have two engines with less thrust.

Hey Kyle,

 

Good explanation below, They are not my words.

 

In the pack inoperative dispatch, the functioning pack maintains a high flow mode to compensate for the inoperative pack. The Fan Air Modulation Valve will also open fully on the engine supplying bleed, because the single pack operation in high flow mode requires cooler input bleed air. The operation of one pack in high flow mode therefore requires that the EPR on that engine be further reduced (relative to normal pack flow) to maintain EGT margin at the higher fan and core bleed level. Because the thrust management system will not permit any significant thrust asymmetry to be set, both engines will be throttled back to the lower level.[/size]

The net effect is that both engines are producing less thrust in the Pack Inoperative dispatch even though only one is supplying bleed air, at a higher rate, to supply the single operating pack. Also, after the assumed engine failure, the operating engine maintains the lower EPR value initially set, so the thrust in the one pack inoperative case is lower throughout the takeoff manoeuvre.[/size]

Also good info.....but about the wrong problem if I am not mistaken.

 

We dont have a Pack inop, we have no air from one side.

 

Thus two packs operating on one engine!

 

 

Good explanation below, They are not my words.  

We dont have a broken pack in this example.

PRSOV - Pressure Regulating and Shut Off Valve.
So you are missing the bleed air from the right engine and now the left engine has to supply air to both packs.
And thus it has LESS thrust available.

I guess the EEC will reduce the thrust on the other engine automatically to prevent assymetric T.O. thrust. So you have two engines with less thrust.

 

Thanks guys!