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-   -   No Bleeds off takeoff (https://www.pprune.org/tech-log/639605-no-bleeds-off-takeoff.html)

argyle 1st Apr 2021 08:41

No Bleeds off takeoff
 
Does anybody know why you are not allowed to do a Bleeds Off takeoff on PW 4056 powered B747-400 freighters?

dixi188 1st Apr 2021 09:59

First thought, IIRC,on all 747s the leading edge devices are air operated so if bleeds are off what holds them out?

mustafagander 1st Apr 2021 10:52

Why would you want to perform a bleeds off take off? Packs off as is common reduces the bleed air extraction to almost zero.

speed freek 1st Apr 2021 13:34

Think something lost in translation. We have one PW powered jumbo. Can't do a "packs off" or "APU to pack" take off. Nothing about bleeds.

No idea either by the way as to why it's not allowed. Been asking the question myself and not getting an answer.

CCA 1st Apr 2021 15:32

APU to pack and packs off takeoffs are allowed on PW4062 powered B747-400ERFs.

Regarding the leading edge flaps they are mechanically extended via pneumatic or secondary electrical.

There was an accident within the first years of 747 service where a bleeds off takeoff was attempted however the bleeds were selected off prior to selecting flap. So the leading edge failed to extend. The green LE extended lights were then added and thus the call “20/20/green” to cover the inboard, outboard and leading edge flap positions.

speed freek 2nd Apr 2021 16:05

Ours is a BCF. Can't imagine what differences exist between it and the ERFs but our manuals specially prohibit packs off and APU to pack.

It's the only one I've come across with this limitation.

Intruder 3rd Apr 2021 02:48

Packs Off takeoffs are prohibited in our "400C" airplanes - a converted Combi and a BCF. Both have extended upper decks, no nose door, and GE engines. They are also prohibited on the LCFs with PW-4056 engines.

tdracer 3rd Apr 2021 19:08

I don't know about your '400C' freighters, but the LCF doesn't have an APU (no easy way to put a fuel line to the APU through the fuselage hinge).

oceancrosser 4th Apr 2021 01:51

Couldn’t they have repurposed the stabilizer fuel tank for the APU? I assume it is unusable for the engines for the same reason.

Check Airman 4th Apr 2021 03:46

I suppose you'd also have to find a way to route air and electricity through the hinge as well.

tcasblue 5th Apr 2021 01:34

Intruder

That's new to me, I have flown pax, straight and converted combi, Boeing freighter with nose door and IAI Special Freighter 747-400's. As far as I can remember, APU to Pack and Packs Off is allowed on all of them. All available as an option in the OPT for performance calculations.

APU-to-Pack Takeoff
After engine start:
LEFT and RIGHT ISOLATION valve switches - OFF
Leave APU running to supply air to pack 2.
Before takeoff:
PACKS 1 and 3 control selectors - OFF
After takeoff:
PACK control selector (One only) - NORM
After engine thrust is reduced from takeoff to climb, position one Pack Control selector to NORM.
PACK control selector (Remaining pack) - NORM
When cabin pressurization stabilizes, position remaining Pack Control selector to NORM.
LEFT and RIGHT ISOLATION valve switches - ON
APU selector - OFF


Packs Off Takeoff
Before takeoff:
PACK Control selectors - OFF
After takeoff:
PACK Control selector (One only) - NORM
After engine thrust is reduced from takeoff to climb and prior to reaching 3,000 feet above field elevation, position one Pack Control selector to NORM.
PACK control selectors (Remaining packs) - NORM
When cabin pressurization stabilizes, position remaining
Pack Control selectors to NORM.


As for a bleeds off takeoff in an aircraft, I seem to remember most of our takeoffs in the 737-200 were with bleeds off as the call during climb was "Climb Thrust Bleeds On".


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