Hi Guys,

 

First Post !!!

 

Hi I have been trying a No Bleeds takeoff as per the Supplementary procedures FCOMv1 SP2.7 and came across a problem.

 

With the left pack on utilizing APU bleed for presurization there is a difference in the calculated takeoff N1 for both engines on both the FMC and Engine display(0.8% diff).  The autothrottle will set the N1 when TO/GA is selected however because of the split there is obviously an assymetric thrust setting.

 

Any ideas as how to solve this issue?

 

It would appear that the status of the pack, i.e. operating or not determines the takeoff N1, even though that pack maybe running off of APU bleed air with no pneumatic load on the engine.

 

Marc Holford

 

 

Sorry for the multiple posts.  The forum gave me an error message when I tried to post, so I repeated twice. 
But obviously each attempt was succesful.

 

Marc Holford

This seems to be a problem with the NGX. The N1 setting should take account of pack, bleed and isolation valve switch positions to calculate the bleed correction. The NGX seems to look at pack air flow and apply a bleed correction on the basis of that alone. It ignores the possibility that the APU is supplying the air. I reported this to PMDG some while ago so I know they are investigating.

 

 

Sent from my iPhone using Tapatalk

And you have both packs in AUTO, right?

Thanks Guys,

 

Kevinh :That is what I thought. 

 

 

Matt C : Yes both packs in Auto but in that scenario only the Left Pack would be operative as that would be getting air from the APU.

 

Marc Holford

@Marc

 

Both engine bleed switches are OFF right?

 

>With the left pack on utilizing APU bleed for pressurization...

 

One small caveat if I may: The primary reason the APU bleed air is being used during a No Engine Bleed Takeoff is for passenger comfort from an air temperature and air flow stand point. (Meaning the APU bleed air is operating the left pack). It would not be to provide pressurization. While the APU bleed air does provide some pressurization, that is a secondary concern.

 

So, your statement is correct but I wanted to mention 'the other reason' as well 

 

During the take off, pressurization is not an issue but passenger comfort is. The engine bleed switches are turned ON right after take off and so, that is when pressurization would really get going.

Yes both bleeds switches are off.

 

I refererenced the supplement to perform the procedure.

 

Thanks yes I had realized the pack would provide air conditioning as well but did not write it in the original post.

 

Nice work on the autoland presentation by the way.  It was very well done.

 

Marc Holford

>Nice work on the autoland presentation by the way.  It was very well done.

 

Thank you Marc. I was amazed at how many people have viewed it...almost 450 views in 48 hours. I guess there is a lot of interest in flying CAT III autolands lol.