747 main gear - selectable?

[Hay Ewe]

Just been talking with a guy who says the the main gear on a 747 is selectable and that the wing gear or the main gear can be selected down for landing?

i.e. not all four legs extended.

Is this so?

Doesnt seem right to me, but have been known to be wrong before....


Hay Ewe - got your gear down?

[SnapOff]

Nope, one handle controls all 5 legs. In a inop gear lever scenario, the main gears and doors are released by electrical rotary actuators and fall with the aid of gravity, the system being controlled by a switch, however the nose gear has to be wound down by a handle down in avionic (lwr 41) bay. Blimey didn't know I could remember so far back!!

[SeldomFixit]

Was there not a Wing L/G only selection available at one time ?

[TopBunk]

SnapOff

I think you may be remembering too far back, maybe the Classic!

On the -400 there are 2 guarded alternate gear extension push button switches to the right of the Landing Gear Lever. One is for the Nose and Body Gear, t'other for the Wing Gear.

My notes would suggest they are only used in abnormal Gear Disagree conditions.

[VTM]

SNAPOFF,
All 5 gears on the classic can be selected independently, by 5 switches on the overhead panel, they are only used in abnormal situations ie loss of hydraulics for systems 1 or 4. Nose gear manual extension only used if hydraulic and electric extension fail to operate.
The 744 has only 2 switches as previously mentioned.

VTM

[SMOC]

The 747 used to have a selectable Gear as you can see from this photo:

http://www.!!!!!!!!!!!!!!/open.file/349788/L/

I believe it was a form of speed brake possibly for an emergency decent, it was later found to be redundant so disabled. I saw the modification on a Polar Air Cargo some years ago so a mate and I followed it up and discoverd the wing gear used to be able to be selected down independantly.

[SeldomFixit]

Thank you SMOC - pleased to see I've remembered something after all.
Now - who remembers the surge tank suppression system..............?

[gas path]

....Or even the standby hydraulic system.....

[SeldomFixit]

Sad, but I do

What about MSAS ?

[gas path]

Nope you got me on that one! was it that stability augmentation thingy? You must be a lot older than me
Anyway how about JT9D-3a with all them bleed valves and turbine thrust reversers?

[SeldomFixit]

Modal Stability Augmentation System - keerekt.

Not sad this time though because the less I remember about 3A's ( which I'm sure remained under development up to and including the -4000 before they got it right ) the happier I am.
Have wrestled all the ones you mentioned.

Now - thinking caps on - MSAS had a " sister " system. remember what that one was ???

[Perrin]

From one who had the trill of working on the -3 was it the RABS
system?

[SeldomFixit]

Perrin, although the mere mention of anything with a 3 in it ( -3A - 3.0 Bleed, - 3.5 bleeds ) gives me the shivers, I was after the " sister " system to MSAS. It was a second stability augmenter that used an accel in front ( from memory MSAS was one in the bum and one under the centre lavs ) or vv, but I can't remember the name of the second system. A 3 letter name rings a bell but only VERY faintly.

And for even daring to mention RABS - go and sit in the corner boy !!!

[gas path]

Give us a clue what 3 letter name rings that bell?

Anyway as an aside and thinking of RABS who remembers the 15th stage bleed valves with pressure switches....... or diff. pressure switches depending on the mod state. and why were there 2 different types?

[SeldomFixit]

Well, that's the problem you see I'm old and just don't remember, which is why I was hoping an erudite PPruner would come to my aid
Was it GRS ? ( gust response system )