Ok i'm planning a flight out of EGLC RWY 09 and i'm getting perf limit - 64,805 kg i try PACKS OFF and the perf limit increases to 65,205 kg why does this increase? i drop my cargo from 4500kg down to 3000 kg still in the red perf limit.

 

my flaps are 25

 

thrust is TO

 

LIMIT CODE is FIELD

 

I have dropped my PAX loading to 1 and cargo 100kg still in the perf limit 

sorry mean't to say at the last part by dropping weight it came out of the red perf limit.

What's your question actually?

I performed a packs off takeoff but my perf limit increased?

With packs off, you get a slightly higher N1, so a little bit more power allows you to take off with more weight.

Ok i'm planning a flight out of EGLC RWY 09 and i'm getting perf limit - 64,805 kg i try PACKS OFF and the perf limit increases to 65,205 kg why does this increase? i drop my cargo from 4500kg down to 3000 kg still in the red perf limit.

 

my flaps are 25

 

thrust is TO

 

LIMIT CODE is FIELD

 

I have dropped my PAX loading to 1 and cargo 100kg still in the perf limit 

sorry mean't to say at the last part by dropping weight it came out of the red perf limit.

 

The guy above is right. If you leave the aircondition packs on engine bleed you will "steel" air from the engines. If you switch off the packs you have additional air for the take off. You have more engine thrust thus your limit rises.

 

I dont know the NGX in the sim but i know the E190 in real, so if it is possible you could choose a static take off and/or calculate for a full thrust take off instead of a flex take off. I gues you have full thrust T/O as you want to fly off LCY.

Yes thats understood i just couldn't understand why my perf limit increased due to packs off but i see now!

 

how can you work it out when to use packs off?

In order to cool and pressurize the cabin turbine engines take air from the compressor called bleed air. If the bleeds or packs are off this air is not bleed from the engine allowing for the engine to generate more thrust therefore, the takeoff weight can be increased.

Yes thats understood i just couldn't understand why my perf limit increased due to packs off but i see now!

 

how can you work it out when to use packs off?

Obviously, only when you cannot achieve it with packs on.

Got ya cheers!! just tried a few takeoff weights with PFPX and doing a packs off gives me extra weight to take I'll leave the APU on for pax comfort since i'm nice that way lol

Basically there are 3 types of takeoff: Bleeds ON, Bleeds OFF, and unpressurized.

 

Don't make the mistake of calling a Bleeds OFF takeoff a PACKS OFF. You are still using the APU to supply bleed to the R PACK and both PACK switches are ON.

 

If you can't make the T/O with the Bleeds ON, you might with the Bleeds OFF with the added performance. You'll get 800lbs more if you're runway limited and something like 2600lbs more if you are climb limited.

 

You'd do and unpressurized takeoff if you needed to have the Bleeds OFF and you had an APU that was not working (MEL'd).

Oh, and there's no credit for a STATIC takeoff on the 737.

Yeh the normal procedure is a bleeds on takeoff. If you are perf limited a bleeds off takeoff can be used provided the APU is available (like my case above) You are correct, mixing them up and having switching the packs off with APU running to pressurize the cabin. then the aircraft would depart unpressurized and you will prob have your wings clipped and be having a hearing with the gaffer haha.

 

 

then the aircraft would depart unpressurized and you will prob have your wings clipped and be having a hearing with the gaffer haha.

 

Not necessarily...

 

Unpressurized isn't a huge deal until you get higher up.  If you depart at sea level, you have some time to reconfigure, but for the comfort of the passengers, this is usually unnecessary and avoided.