737 bleeds off takeoff

[TotalBeginner]

Supplementary procedures state that if engine anti ice is required for taxi, then bleeds off configuration should be delayed until just before takeoff. But if conditions exist that require TAI to be used during taxi, then surely it’s likely that it will need to remain on for takeoff too?

[FlyingStone]

Bleed configuration has no effect on engine anti-ice, as the air comes directly from 5th/9th stage.

The issue is more with wing anti-ice, which is used in icing/freezing condition on the ground (unless aircraft is protected by Type II/IV de-icing fluid). Wing anti-ice should not be used with bleeds takeoff, as isolation valve is closed in that case, meaning only left wing would receive air for wing anti-ice.

Wing anti-ice is off during normal takeoff as well (valves close when thrust levers are advanced for takeoff), and it is very rare that you would need to use it immediately after takeoff.

[ImbracableCrunk]

I'm not sure you'd ever need to do a bleeds off takeoff if the temp if below 10C.

[FlyingStone]

Originally Posted by ImbracableCrunk

I'm not sure you'd ever need to do a bleeds off takeoff if the temp if below 10C.

Why not? If you are performance limited at 11C OAT, it's not going to get any better with 1C less and engine anti-ice on - quite the opposite.

[Johnny F@rt Pants]

I'm not sure you'd ever need to do a bleeds off takeoff if the temp if below 10C.

What a load of rubbish.

Example, taking off from say Jersey in the winter cold wet weather, you’ll definitely be performance limited and will need to use bleeds off if your payload requires it.

[tdracer]

Depends on the engine and the aircraft installation, but 'bleed debits' to the max TO rating are often automatic and independent of OAT.

[TotalBeginner]

Originally Posted by FlyingStone

Bleed configuration has no effect on engine anti-ice, as the air comes directly from 5th/9th stage.

The issue is more with wing anti-ice, which is used in icing/freezing condition on the ground (unless aircraft is protected by Type II/IV de-icing fluid). Wing anti-ice should not be used with bleeds takeoff, as isolation valve is closed in that case, meaning only left wing would receive air for wing anti-ice.

Wing anti-ice is off during normal takeoff as well (valves close when thrust levers are advanced for takeoff), and it is very rare that you would need to use it immediately after takeoff.

like an idiot I misread it. It states anti-ice, not engine anti-ice and therefore must be referring to wing anti-ice.

I’m not sure I can think of a time when wing anti-ice would be used during taxi though. Are there operators that use it along with fluid treatment?

[FlyingStone]

Yes, as per Boeing procedures:

Use wing anti-ice during all ground operations between engine start and takeoff when icing conditions exist or are anticipated, unless the airplane is, or will be protected by the application of Type II or Type IV fluid in compliance with an approved ground de-icing program.

[ImbracableCrunk]

14 years of rubbish

Originally Posted by Johnny F@rt Pants

What a load of rubbish.

Example, taking off from say Jersey in the winter cold wet weather, you’ll definitely be performance limited and will need to use bleeds off if your payload requires it.

14 years on the type at two airlines and I’ve never needed bleeds off in cold weather ops. It’s always been summer ops. But I’ve never flown to Jersey.