Performance calculation with one pack inop

[WhiteKnight]

Hi,
just had this problem: Boeing 737-800 left pack inop.

Mel reads:


When dispatching with one pack operating by engine bleed air on takeoff:
A)Determine V1(VMCG) based on engine bleed for packs off
B)Determine takeoff performance on packs auto

How and why do you have to do this?

We have a performance program on a laptop where you can choose between an engine bleeds on or an engine bleeds off takeoff. So are you doing than 2 calculations. First with engine bleeds off, taking the V1, and secondly a calculation with engine bleeds on for the other data? Or what??

Furthermore the MEL reads:
For increased airflow when the flaps are extended(takeoff and landing) use apu to supply bleed air to the operating pack.
Left pack inop:
1) Engine no1 bleed air switch off
2) Right pack switch auto
3) left pack switch off
4)Isolation valve switch open
5)engine no 2 bleed air switch off
6)Apu bleed air switch on


So if you do this configuration, you operate the left pack from the Apu, and you can do just an engine bleeds off calculation. Am I getting this right?

So you don`t have to takeoff with one pack operating by engine bleeds, except you`re APU is broken, right?

Can someone clear this a little bit up. I would be very grateful.
Thanks

-Whiteknight

[IRRenewal]

Reading that I'd say you determine all performance data based on 'packs auto', than check that the resulting V1 is higher that Vmcg for packs off.

You're combining two worst cases. Single engine T/O performance with the operating engine running a pack (lowest thrust of the two), and single engine controllability when the operating engine is not running a pack (highest thrust of the two).

So if you do this configuration, you operate the left pack from the Apu, and you can do just an engine bleeds off calculation. Am I getting this right? Correct

So you don`t have to takeoff with one pack operating by engine bleeds, except you`re APU is broken, right? Correct. But if you have enough performance available, why would you?




Just checked our DDPG (B738) and it says:

When dispatching with a single pack on for takeoff (airplane pressurized), VMCG should be determined based on AC packs OFF.
Takeoff performance should be based on AC packs ON/AUTO.