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Hydraulic Failure  
User currently offlineBDABOY From Bermuda, joined Nov 2004, 110 posts, RR: 0
Posted (6 years 8 months 1 week 5 days 1 hour ago) and read 12880 times:

What is exactly involved in a hydraulic failure? I ask after an incident on the 6th of november when our BDA bound flight on an American 757-200 suffered, as the pilot described it, a failure of the main hydraulic system, about 4 minutes into the flight. We had experienced some moderate turbulence for about a minute before the announcement, and I remember thinking it felt rather strange ( I have flown a lot in my life so I have a few bouts of turbulence to compare it too!! ) but I am prepared to accept that as just coincidence. The pilot informed us that the backup system(s) was working well, and that he would have to do a series of checks before we could head back to JFK. Indeed we landed about 20 minutes later after some low altitude (it seemed) circling, and were immediately surrounded by more fire engines than I've ever seen in one place.

I am wondering several things. How dangerous a situation was this? What exactly do the hydraulics control? Do you think the "turbulence" was associated with it? What procedures did the pilot have to go through before we could land?
Any insight would be appreciated. Forgive my ignorance. Despite a long interest in aviation I find myself sadly lacking in detailed technical knowledge, and this is my first post in the tech/ops forum.

16 replies: All unread, jump to last
 
User currently offlineJetMech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 1, posted (6 years 8 months 1 week 5 days 1 hour ago) and read 12886 times:



Quoting BDABOY (Thread starter):
What exactly do the hydraulics control?

Hydraulics provide the power to move stuff such as flight controls and landing gear, so such systems are very important on modern commercial aircraft. It is hard to say what constituted the main hydraulic failure on your flight. I have never worked on a 757, but I assume it would have three hydraulic systems like a 767.

The hydraulic failure may have been a partial or full failure in one system. Perhaps one of the pumps failed on one of the systems and a back up had to be used? Perhaps there was a leak which entirely disabled one system such that you were only flying on two systems? It is hard to say without knowing more details.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineFr8Mech From United States of America, joined Sep 2005, 5355 posts, RR: 14
Reply 2, posted (6 years 8 months 1 week 5 days 1 hour ago) and read 12884 times:

The 757 has 3, count them 3, main hydraulic systems. Left, Center & Right. The failure of any one or even two systems does not put the aircraft in any serious impending jeopardy. Modern aircraft are designed to operate just fine with the loss of one of the systems. Redundant actuators and back-up systems, usually electric, usually prevent scary scenarios.

The fire trucks are a precaution.



When seconds count...the police are minutes away.
User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9497 posts, RR: 52
Reply 3, posted (6 years 8 months 1 week 5 days ago) and read 12856 times:

Everything has at least one backup when it comes to hydraulics. Some have redundant hydrualic controls. Some have redundant electric controls. There are at least two systems that can power anything used in flight.

Hydraulics are needed for flight controls (elevators, rudder and aeilerons) as well as flaps, spoilers and gear retraction. The gear on many planes can be deployed without the use of hydraulics, although it normally does need hydraulic pressure.

I can't imagine turbulence causing the loss of one of the hydraulic systems. Probably, either a pump, actuator or line failed. Usually it is a pump which is powered by either the engine or electric power that fails. Turbulence will not effect these. If the pump already has a problem that is causing it to slowly fail, then a bit of turbulence could put it over the edge. However usually failures are caused by a large hydraulic system demand, such as when the landing gear is being retracted while other systems are being used such as flaps and control surfaces.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (6 years 8 months 1 week 4 days 21 hours ago) and read 12824 times:



Quoting BDABOY (Thread starter):
What is exactly involved in a hydraulic failure?

Could be pretty much anything in the system (filter, pumps, line somewhere, etc.). By far the most likely cause is a flakey sensor somewhere saying something is bad when it actually isn't. The flight crew gets fairly limited error messaging on the flight deck.

Quoting BDABOY (Thread starter):
How dangerous a situation was this?

Not at all. Loss of one system, as described well in previous posts, doesn't cause the loss of any aircraft functions.

Quoting BDABOY (Thread starter):
Do you think the "turbulence" was associated with it?

Nope, unless the motion from the turbulence finally popped a bad coupling or wiggled a sensor wire just right. In other words, the turbulence might have been cause, but almost certainly wasn't a result.

Quoting BDABOY (Thread starter):
What procedures did the pilot have to go through before we could land?

It really depends on what specific error the flight crew got. Typical things are to verify the operation (or not) of the systems that that hydraulic circuit controls and see if the power transfer unit is working. The crew has a defined list of checklists to do in a situation like this and "hydraulic failure" could encompass one or more of about 8 procedures, some of which call out other checklists.

Tom.


User currently offlineWirelock From Spain, joined Sep 2007, 126 posts, RR: 0
Reply 5, posted (6 years 8 months 1 week 4 days 13 hours ago) and read 12767 times:



Quoting BDABOY (Thread starter):
Indeed we landed about 20 minutes later after some low altitude (it seemed) circling,

this could have been to dump fuel so that the aircraft was not overweight on landing. not familiar with B757 but i assume it has this provision


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 6, posted (6 years 8 months 1 week 4 days 13 hours ago) and read 12766 times:



Quoting Wirelock (Reply 5):
this could have been to dump fuel so that the aircraft was not overweight on landing. not familiar with B757 but i assume it has this provision

Nope. The 757 has no fuel dump.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineWirelock From Spain, joined Sep 2007, 126 posts, RR: 0
Reply 7, posted (6 years 8 months 1 week 4 days 12 hours ago) and read 12754 times:



Quoting Dl757md (Reply 6):
Nope. The 757 has no fuel dump

cool... everydays a school day when it comes to aviation


User currently offlineAAR90 From United States of America, joined Jan 2000, 3466 posts, RR: 47
Reply 8, posted (6 years 8 months 1 week 4 days 10 hours ago) and read 12723 times:



Quoting BDABOY (Thread starter):
How dangerous a situation was this?

A single system failure... virtually no change in your safety.

Quote:
What exactly do the hydraulics control?

Essentially all the "big" mechanical devices along with flight controls, brakes, etc.

Quote:
Do you think the "turbulence" was associated with it?

Probably not.[/quote] What procedures did the pilot have to go through before we could land?[/quote]Varies depending upon which of the three (L-C-R) systems experienced the "failure" and what type failure it was. If you could provide the flight number/date/stations, I _might_ be able to pull up the acft's maintenance log for more detailed analysis.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineBDABOY From Bermuda, joined Nov 2004, 110 posts, RR: 0
Reply 9, posted (6 years 8 months 1 week 4 days 8 hours ago) and read 12691 times:

AAR90, the flight number was AA1444, JFK- BDA on November 6th, scheduled departure was 5.20 p.m. I seem to recall.

Thanks for the replies everyone. I just remembered the pilot saying he didn't think it was a good idea to head out over the Atlantic with the system down. Everyone laughed thinking he was joking, but would it have been a consideration at all with the 2 backup systems operating normally?


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 10, posted (6 years 8 months 1 week 4 days 8 hours ago) and read 12679 times:

Firstly Intersting username.....Any reason.

The B752 is a fantastic Aircraft in terms of backups.
it has the Left [1EDP + 1EMDP],Right [1EDP+1EMDP],Centre [2EMDP]...Add in the RAT,PTU & if ETOPs enabled craft the HMG or HDG.

A single or Dual Hydraulic failure can still be controlled efficiently.
The RAT will deployed for a more serious case.

Trust me its a great aircraft.

regds
MEL



Think of the brighter side!
User currently offlineFr8Mech From United States of America, joined Sep 2005, 5355 posts, RR: 14
Reply 11, posted (6 years 8 months 1 week 4 days 7 hours ago) and read 12666 times:



Quoting HAWK21M (Reply 10):
HMG or HDG.

We've been over this...this is not a source of hydraulic power, it is a user.

Quoting BDABOY (Reply 9):
Everyone laughed thinking he was joking, but would it have been a consideration at all with the 2 backup systems operating normally?

No, a hydraulic failure, whether single system or multiple, should get the pilot thinking about landing. It should certainly give him pause if the routing is across a large body of water.

Though the systems are isolated, some of the systems do share a component or two. Left and Right share an automatic brake selector valve (or some such thing) which if it failed could result in a dual system loss. A PTU failure could result in a L/R loss. A very few other things. And by failure I mean a physical failure such as a rupture of the valve body (extremely rare).



When seconds count...the police are minutes away.
User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9497 posts, RR: 52
Reply 12, posted (6 years 8 months 1 week 4 days 5 hours ago) and read 12633 times:



Quoting BDABOY (Reply 9):
I just remembered the pilot saying he didn't think it was a good idea to head out over the Atlantic with the system down. Everyone laughed thinking he was joking, but would it have been a consideration at all with the 2 backup systems operating normally?

Losing a hydraulic system doesn't require landing at the nearest available airport, but it does warrant a diversion. You never know why it failed for sure in the flight deck. If one system goes down, then the probability of another going down does increase. Although there is redundancy and few places where the systems interact with each other (there is no direct transfer possible between the systems) it is a good idea to land. BDA does not require ETOPS operations, but it is a pretty stupid idea flying there with a system down. There are no alternates and only one runway.

Hydraulic failures are rare. For example, on the 737, I've only ever heard of one instance where the two main hydraulic systems failed.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineAAR90 From United States of America, joined Jan 2000, 3466 posts, RR: 47
Reply 13, posted (6 years 8 months 1 week 4 days 4 hours ago) and read 12608 times:

Okay BDABOY, here you go. Let us know whatever you can't decipher from below:
---------------------------
From Daily Operations Summary:
-1444/06 N619 JFK-BDA RTND JFK ACCT LH HYD QTY LOSS. EMGCY DCLRD. LNDD OVRWT W/OUT INCDNT. ACFT OTS. FLT RON ACCT BDA CURFEW.

From Acft Electronic Maintenance Log (the problem):
LEFT HYD QTY EICAS MSG AND RSVR LIGHT ILLUMINATED
IN CLIMB TURNED OFF L ELEC HYD PUMP @ L ENG HYD
PUMP WITJ .45 QTY REMAINING RAN ALT FLAP AND ALT
GEAR CHECK LISTS

The maintenance reply (action taken):
FACT.06NOV/JFK/AC
REPLACED RT WHEEL WELL DOWNLOCK ACTUATOR PRESSURE
AND RETURN LOSES AND OPS CK GOOD.

More log entries documenting phone conversations between TULE engineers & JFK maint.techs as well as action taken on this event:
MDIS.06NOV/TUL
ACFT HAS HAD A/I DUE LT HYD QTY LOSS. PER TELECON
WITH JFK TECH CC. THE LEAK IS IN THE RIGHT W/W.
EVALUATE AND REPAIR. PLEASE UPDATE THE HYD LEAK
WEBSITE. INFORM TECH SERVICES OF PARTS AND
MATERIALS NEEDED

ATBT.07NOV/TUL
1 EVALUATE AND REPAIR PER FINDINGS, UPDATE HYDRAULIC
2 WEB SITE, ADDRESS IS HTTP://ME.AA.COM/MESI/SIC/ SO
3 ENGINEERING CAN ADD TO DATA BASE.

FACT.06NOV/JFK/AC
REPLACED RT WHEEL WELL DOWNLOCK ACTUATOR PRESSURE
AND RETURN LOSES AND OPS CK GOOD.
------------------------------
Were you in danger? No.
Good decision to return to JFK? YES.
As others have noted, "not a big deal" but one you don't want to continue the flight with --you don't know WHY the quantity was decreasing at that time. Only system that was not "working" was the ALTERNATE wheel brakes, but the NORMAL and EMERGENCY systems were working properly.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineBDABOY From Bermuda, joined Nov 2004, 110 posts, RR: 0
Reply 14, posted (6 years 8 months 1 week 4 days 1 hour ago) and read 12578 times:

Once again, many thanks for the replies.

AAR90- that log makes fascinating reading! I think I got pretty much all of it except "EICAS" message, and left engine hydraulic pump "WITJ".

I love the 757, especially the whopping take off, and this is the only problem I've ever encountered on one after many, many flights.

P.S. HAWK21M, my user name means simply,"the boy from Bermuda".


User currently offlineFr8mech From United States of America, joined Sep 2005, 5355 posts, RR: 14
Reply 15, posted (6 years 8 months 1 week 4 days ago) and read 12570 times:



Quoting BDABOY (Reply 14):
I got pretty much all of it except "EICAS" message, and left engine hydraulic pump "WITJ".

EICAS = Engine Indicating Crew Alerting System. When looking at a B757/767 cockpit, the 2 screens in the middle are the EICAS displays. The EICAS computers gather information from the various systems/sensors arrayed throughout the aircraft and display certain information on the screens.

WITJ = That's probably a typo. It should be "with" as in "with .45 qty remaining". Very important information. It means the pumps did not run dry and maintenance would not need to replace them.



When seconds count...the police are minutes away.
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 16, posted (6 years 8 months 1 week 2 days 9 hours ago) and read 12478 times:



Quoting Fr8Mech (Reply 11):
We've been over this...this is not a source of hydraulic power, it is a user.

True.....I wonder Why I put that in.Apoligies.

Quoting BDABOY (Reply 14):
P.S. HAWK21M, my user name means simply,"the boy from Bermuda

ok.

regds
MEL



Think of the brighter side!
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