B737NG - PTU + Alternate Flaps System?

[ATRflyer]

Hi all,

Just doing a bit of preparation before commencing training on the B737NG by reading through the boeing manuals and also the 737NG Cockpit Companion. I have being looking over flight controls and hydraulics recently and just wondering if anyone out there can help me out with these couple of questions?


1) If in the unlikely event of having a failure of both system B hyd pumps (system B reservoir quantity still full), would the PTU still be capable of extending/retracting the LE devices and Autoslat operation?

I ask this because I get the impression from reading about the PTU in the manual that it is there mainly as a backup incase the output pressure from the System B engine driven pump is low, and isn't really designed to work with the loss of both system B pumps?


2) In relation to the Alternate Flaps System, it is mentioned that the leading edge devices will remain extended if you put the alternate flaps toggle switch in the 'UP' position. Does this only apply if you had first selected the LE/TE devices down with this switch or would it actually be possible to first select both LE + TE devices up, if they were already extended before you lost system B?


Thanks in advance,
All the best,

Atrflyer

[ifleeplanes]

1) Should there be a failure of both the Elec and Mechanical pumps then the PTU will power the LE Flaps and Slats and Auto slats, using system A pressure but using system B fluid.

2) The alternate flap switch operates the TE devices electricaly, with the switch closing a value to prevent a hydraulic lock and allowing an electric motor to extend/retract the flaps.
If the LE devices were already out you would be stuck with them out since it uses hydraulic power from the standby system via a standby pump to extend only. The TE devices could be retracted but VERY slowly

Hope thats of some help...good luck. who are you off to work for?

[ATRflyer]

Thanks very much for your help and responding so quickly ifleeplanes, appreciate it.

I thought everything was straight forward when the manual mentioned that the standby system can only extend the leading edge devices, but it was the following paragraph out of page 30 of the cockpit companion that really confused me:

Note: PTU control valve closes when the Alternate Flaps Master switch is moved to ARM and the Alternate Flaps control switch is moved to DOWN; this stops PTU operation.

- if you loose B sys hydraulics and flaps are extended (after takeoff), the LEDs can be retracted with PTU pressure using the Alternate Flap system.

- PTU would not be inhibited because the control switch was not moved to DOWN.


I thought the PTU and the Alternate Flap system were two completely different systems or maybe I am just getting confused at the way it is worded?


Joining Ryanair, looking forward to moving onto the 737 and getting plenty hours up. Will miss flying the ATR though, it's a great aircraft and a pleasure to fly.

Thanks again for your help ifleeplanes.

Regards,
Atrflyer

[ifleeplanes]

If you had just got airborne the Standby Hydraulic System would operate automaticaly since for automatic operation it requires that :
1) Airborne and
2) Loss of System A or B and
3) Wheel speed >60kts and
4) Flight control A or B switch is on
ALL the conditions have to be met. Thus takeoff is one such occurence. When it operates it only allows LEDs to extend.

Hope you enjoy the flying, dont delve too deeply into the mauals it can get confusing. All you need for the exams is in the Boeing manuals, the Cockpit companion is great for just that...the cockpit.

[ATRflyer]

Thanks again for your help and advice ifleeplanes.

I'm certainly looking forward to it all. Should be great.

I promise not to ask ya any questions like that if we fly together some day!!

Thanks again.