NG standby RUD
 

Reference the FCOM, selecting stdby RUD on causes;

shuts off the related hydraulic system pressure to ailerons, elevators and rudder by closing the flight control shutoff valve

Why would you want this? I would think opposite, low overall system pressure the last thing you want is less control of aircraft?

Confused!

Also, why are the LE flaps and slats are heavy load items? Hence PTU!

The Primary Flight Controls can be operated completely by either System A OR System B hydraulics so a loss of just one system will have no effect on the basic controlability of the aircraft.

Positioning ONE of the FLT CONTROL switches to STBY RUD activates the standby system as well as shutting off access from the normal system A or B as you say.

The standby system's main purpose (IMHO) is in the "worst case" scenario of failure of both A AND B system (manual reversion) where power to the rudder and the standby yaw damper assist controlability, leading edge slats/flaps extension and thrust reversers assist performance.

With failure of only a single system (A OR B) the standby system is (somewhat) unnecessary....but nice to have anyway, in a manual reversion it shines! :ok:

Manual reversion an interesting SIM exercise - in a small way to feel how heavy the aircraft is but, more interestingly, how to best use CRM and cockpit duties to best handle an exercise that is physically demanding and tiring.

Mr Boeing says the PTU is there to provide volume of hydraulic fluid to allow operation of the LEFlaps/autoslats/slats at the "normal rate" when system B is lost; the electric pump only provides 1/6th of the volume of a mechanical pump hence the PTU to use the A system mechanical pump if required.

That's the way I read what Mr Boing says about "stuff", happy to be corrected anytime.
Cheers.

Good answer.

But turning the flight control shutoff valve has any other advantages. Simply why isolate the normal system?

PTU: I thought other systems would require it's use also?

Selection of Standby Rudder means you'd already have low flight control hydraulics, usually a sign of a leak. You close the shutoff valve to stop losing anymore.

Manual Reversion is the only thing I have found easier in the sim compared to the aircraft :ooh:

Only had the "pleasure" of looking at manual reversion in the SIM a couple of times.
If indeed more difficult again in the real beast then even more "fun, fun, fun"!

However I'll tempt the aviation gods - "what's the chances of ever having a manual reversion in the real world"??:}
Cheers

All these items you mentioned (ailerons,elevatirs,rudder) have redundancy,if one system is inop (A or B) then the other will still provide sufficient volume/pressure to operate them,if not then an secondary source is used(ie TE flaps electrical motor).
Why would you want a line of fluid open with no or too little fluid/pressure supplying it?
It could be simply that under a certain pressure,the above flight control cannot simply be operated.For example,If you lose engine hydr pressure only the electric will take the load but may be struggling to cope with the required pressure demand for the flight controls it operated and low pressure may illuminate.If you lose both pumps then they cant be operated.
A and B hydraulics dont mix.
The standby rudder is powered when the switch is in Stby rudder,useful when you plan on landing in windy conditions.

The PTU will not work if you have lost System B fluid...only if its pressure has dropped under a specific value (2350psi).
It then uses A pressure but B fluid.

Sure about that? Even with a loss of system B there should be enough fluid under the standpipe level for PTU operation.

Assuming the reservoir itself is not leaking and the reason for your leak is a pump/line failure.

I am saying that the PTU works when B PRESSURE is below 2350psi, if you have lost SYS B fluid(yes all of it) then it wont work.

:ok: I just hope it's been properly rigged or you'll have an.....interesting ride :eek:

That is why the maintenance manual requires a hyd power off elevator check flight if the elevator trim tab has been disturbed. I have had one check flight when the setting was not correct and it is a little exciting until you overpower or get the hyd power back on.

The aircraft flys very well in manual reversion, in the 5 different B737-200, 300 and 400 simulators I have used three were very close to the aircraft feel, one was OK and one was so bad the regulator required manual reversion training to be completed in the aircraft or another simulator used.

C100, the most interesting manual reversion air test I've done was a pre C check flight. 18 turns nose down!

Holy cow! That is far too much excitement for me!

Last manual reversion in the Ng aircraft three weeks ago required 9 turns of NU trim.