Hi all!

 

My question is regarding packs on/packs off takeoff. When I choose packs to be on during takeoff via the FMC takeoff page, I get a higher N1 value than if I had chosen a packs off takeoff mode. I'm somewhat confused since I thought that when using packs on the engines would produce less power causing the lower N1 value.

TOPCAT gives me lower N1 when choosing packs to be on during takeoff, which is what I also expect, but not the simulation itself.

 

Is there anyone who could throw some light on this?

 

Thanks in advance!

 

Simon Larsson

I thought that when using packs on the engines would produce less power causing the lower N1 value

 

When you are using the packs, the engines produce more power to compensate for the added demand on bleed air. The engine values should be higher.

 

TOPCAT gives me lower N1 when choosing packs to be on during takeoff, which is what I also expect, but not the simulation itself

 

I would use TOPCAT to calculate an assumed temperature and use the FMS to calculate engine parameters and Vspeeds.

When you are using the packs, the engines produce more power to compensate for the added demand on bleed air. The engine values should be higher.

 

Hi Kenny,

 

thank you for your reply, is this true for the MD11 only or does it apply also to the 737NG?

Hi Kenny,

 

thank you for your reply, is this true for the MD11 only or does it apply also to the 737NG?

Check the ops manual.

 

Best regards,

Robin.