737 Questions

[Pete the Pilot]

1.Why does rudder pressure in 737 go to high when there is a depressurisation in B Hyd sys? The manual doesn't mention A Hyd sys??

2.In the QRH there is a speedbrakes extended light checklist as well as the other speedbrake checklists, but, silly me, I cant find the light anywhere??

[stator vane]

you must not be talking about the -300 or -400's.

my QRH only shows SPEED BRAKE DO NOT ARM checklist and that light is on the forward panel just above the fuel guages.

i also do not know of the rudder pressure change.

[john_tullamarine]

Following on from the previous response ..

(a) perhaps you could recheck the title of the light in question ?

(b) you might be thinking of the situation with loss of A and B if the relevant Flight
Control Switches are not positioned to Standby Rudder. Then the loads get quite high and the rudder is near locked out as far as I can tell.

(c) which model are you concerned with ?

[A and C]

Pete i think that you will only find the speed brakes extended light on the 6-7-800 aircraft (900 ?) it is on in flight when the the speed brake lever is beyond the armed position AND te flaps extended more than 10, or rad alt less than 800ft.

On the ground if the speed brake lever is in the down position and the ground spoilers are deployed.

[ 06 September 2001: Message edited by: A and C ]

[stator vane]

ah-ha!

so he must be speaking the B737-Mutant Generation!!!!!!!!
;)

[Pete the Pilot]

Sorry guys, its the -300 series.

I definitely have 'speedbrakes extended' checklist as well as 'speed brake do not arm'.

Rudder going to high pressure is referenced in Vol 2 flight controls (page 9.20.10 ).
Staes hydraulic pressure returns to normal when descending thru 700' when N1 difference between left and right exceeds 45% and if B hydraulic sys depressurises. Can't see the logic of JUST B depressurising............

[CaptainSandL]

Pete,

Since the rudder scares, 737’s are now fitted with an RPR (Rudder Pressure Reducer) to reduce the rudder authority by about 30%. It is clever enough to give you back full rudder pressure at certain critical times ie:

a) During take-off below 1000’ Rad.alt.
b) During approach below 700’ Rad.alt.
c) If a difference of >45% N1 exists between power units.
d) If B-system hydraulic pressure is lost.

Unfortunately it cannot give you back full rudder pressure if system-A is lost because it is powered by system A!

A good article on the 737 rudder system can be found at:
www.b737.org.uk\theruddersystem.htm (http://www.b737.org.uk\theruddersystem.htm)

S & L

[stator vane]

wow, when i wrote my reply, i had my book beside the laptop!!

my airline has not made a peep about this new hydraulic thing. i knew we had reducers, only by reading the tech logs but no text about what it really does.

and the speedbrake also??!!

can i ask which airline gave you that info, or if not was it UK, USA or otherwise??

will talk to my company tomorrow!!

thanks for the info

[Pete the Pilot]

Thanks Captsandl, I didn't know the system was powered by A so that would explain why B is the only one 'backed up'.

[CaptainSandL]

Stator,
I am with a UK operator of classics, but the info is not likely to appear our pilots tech manuals – need to know basis and all that.

Pete,
You appear to be in a minority with your “Speedbrakes Extended” light and checklist. Could you post it here for the rest of us with any accompanying notes?

S & L

[Pete the Pilot]

I've got the Checklist but unfortunately can't find the light!

Checklist:

Speedbrakes Extended.

Condition: The speedbrakes extended light indicates:

*In flight, the speed brake is beyond the armed position with either the trailing edge flaps extended more than flaps 10 or rad alt less then 800'

*On ground the speed brake lever in down detent and the ground spoilers are not stowed.

Speed Brake Lever..........Armed/down detent

If light illuminated on the ground:

Do not take-off.

[CaptainSandL]

Pete

I have never seen this light before on any classic and our maintenance training manual makes no reference to it. Maybe it was installed on –200’s and migrated across if your airline, or the previous owners, operated both types. My guess is it shouldn’t be in your QRH. What do your engineers / fleet managers say? I presume you still have the SPEED BRAKE DO NOT ARM and SPEED BRAKE ARMED lights and this doesn’t replace either of those. Let us know what you find out.

S & L

[Ugly Jet Captain]

I have seen the lite as an option on several "used" aircraft. The light is on when the brakes are out and the speed brake is in use past the arm detent. We quickly deactivated the system for standardization of the fleet. I have also seen the "blow up" light on a few examples that tells you when the falpas blow up to 30 when you pass 156 KIAS with 40 selected.

[steelbird]

We have the speedbrake (extended)light on our a/c(B737-300/400/500).It is located above the accumulator brake pressure indicator on the F/O's panel.
It flashes when in air & the speedbrake lever is aft of the ARMED position & flaps extended beyond position 10.
Cheers! :cool: