Hyd A Press 737-ng
 

Hi,

Take a look at this picture:

http://!!!!!!!!!!!!!!/open.file/294127/M/

Upper EICAS. HYD A P is indicating 0 although the HYD Q is 94%.

What can be the cause of this? Are the pilots taxing with the HYD A System OFF?

I am confused... :rolleyes:

Thank you
Bruno Francescoli.

Unless the flightcrew is taxiing with both Engine Driven and Electric Pumps OFF (unlikely), then I suspect that the most likely cause is an MEL'd System A Hydraulic Pressure Indication System.

Very observant

Boeing procedures recommend that if pushback is conducted without the use of the nose wheel steering bypass pin, system A hydraulic pumps should be off. If they have just completed the pushback, maybe they are using this procedure.

My company uses the bypass pin so both systems are pressurised during pushback.

Are there companies out there that DO NOT use the bypass pin for pushback?

AA

AA,

I agree,I was also going to suggest the picture was taken during/shortly after a pushback without the steering pin.The nosewheel steering is supplied with A sys px so the pumps would need to be off during push to stop the wheels centering and shearing the towbar.

I don't know of any companies not using the bypass pin but there are companies that take the added step of pushing with A system depressurized.
There are operaters out there with all three types of 737 and it would make sense to keep from popping towbars since the older -200's didn't have a bypass.

That may very well be the case, but if you notice...his flaps aren't set.
So either his pumps are off interntionally or his indication is inoperative.

quote"The nosewheel steering is supplied with A sys px"
Some (300+) have an alternate steering switch that allow's "B"system to be used for steering.

Thank you all for the replies.

Excuse me for my ignorance, but what is a nose wheel steering bypass pin?

Once again, thank you
Bruno

Thanks a lot 7p3i7lot, so basically what the Nosewheel steering bypass pin does is that it prevents hydraulic presure to reach the Nosewheel so that Ground Crew may push, turn and do whatever they need to without problems, right?

If this system is not installed (Like in the picture) HYD SYS A should be Turn Off so that no hydraulic presure reaches the Nosewheel since the bypass pin is not installed, correct?

Hope I got it!
Once again, thank you all.
Bruno Francescoli.

Dead right Bruno.
fruitloop,I should have added the word 'normally'.I'm aware of the alternate steering system but as I have never,ever heard of it being used I didn't think it relevant to mention it.

Sorry If I sounded sarcastic Eng123,didn't mean too,but A/C ops requires it to be operated occasionly (how often I don't know..any-one ??).After viewing the Piccy suspected it was the case..If it hasn't been operated recently it can make a racket and give erronous feel for a few seconds (Air in plumbing ??)
cheers

All,

Got it!!

THANK YOU VERY MUCH , appreciate it.

Bruno Francescoli.

Last question, I swear! :p
 

Hi all,

How are you? It's me again, yes I know, sorry :rolleyes:

Do Classic 737 (2/3/4/5) have the nose wheel steering bypass pin option?

Once again, thank you very much

Bruno

BrunoF. None of the 200's had it (that I worked on)All the 3's and 4's did (sorry havn't touched a 5. !!)

The nose strut mounted bypass valve was an option on the -200's.
To muddy the waters a bit more, the pin actually holds a handle in position. The handle actuates a valve which causes the steering control fluid to bypass the steering actuators thus allowing the nose strut to be rotated freely. There's a couple of different valve types so the handle and valve are mounted in different positions on the strut depending on the series of aircraft.
:8

on that pic ,the plane is stationary (gs=0),just after push and engine start. (engines are at idle thrust,and also flaps=0 ) ,and both sys A hyd pomps off.
Many ops recomand sys A off for pushback,as a suppllementary protective meassure.
You don't want to meet some smart guy who'll forget to install the pin.I'd met one who forgot to remove it:ugh: so,why not the opposite?:)

:ok: