zanl188
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737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 6:54 am

Just curious how often dual hydraulic failures (& use of the mechanical reversion) occur on 737s specifically & on other large jets in general.

Thanks

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20061101X01595&key=1

NTSB Identification: LAX07IA014
Scheduled 14 CFR Part 121: Air Carrier operation of Alaska Airlines, Inc.
Incident occurred Thursday, October 19, 2006 in Los Angeles, CA
Aircraft: Boeing 737-790, registration: N614AS
Injuries: 5 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On October 19, 2006, about 0100 Pacific daylight time, a Boeing 737-790, N614AS, returned to Los Angeles International Airport (LAX), Los Angeles, California, after experiencing a dual hydraulic system failure while en route to Licenciado Benito Juarez International Airport (MMMX [MEX]), Mexico City, Mexico. Alaska Airlines, Inc., operated the scheduled international passenger flight under the provisions of 14 CFR Part 121 as ASA flight 250. An instrument flight rules (IFR) flight plan had been filed. The flight departed LAX about 1200.

According to Alaska Airlines flight safety personnel, after entering Mexican airspace at cruise altitude, the flight crew was alerted to a System B hydraulic failure. The flight crew opted to return to the United States. Upon reaching United States airspace the flight crew declared an emergency and returned to LAX. While on a 5-mile final approach to LAX at 2,500 feet above ground level (agl), the flight crew selected flaps to 15 and extended the landing gear. About 800 feet agl, the flight crew was alerted to a System A hydraulic failure, and subsequently lost hydraulic quantity and pressure of System A. At that point, the airplane became difficult to control in the mechanical reversion mode; however, the flight crew was able to land the airplane without further incident at 0330.

Alaska Airlines maintenance personnel, a Federal Aviation Administration (FAA) airworthiness inspector, and personnel from Boeing examined the airplane and noted that the hydraulic failure of System B (the first event) was attributed to a catastrophic failure of the engine driven hydraulic pump. ASA maintenance personnel found a spoiler hydraulic line that had fractured and bled out the System A (the second event) hydraulic quantity leading to the dual hydraulic failure event.

The cockpit voice recorder (CVR) and flight data recorder (FDR) were sent to the National Transportation Safety Board headquarters in Washington, D.C., for readout.
Legal considerations provided by: Dewey, Cheatum, and Howe
 
troubleshooter
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 4:16 pm

Such failures are fortunately very rare.

In the past years I´ve experienced two events of a full hydraulic system loss: a broken hydraulic line on a Fokker 100 main landing gear and a hydraulic EDP leakage (broken pump case) on an EMB145. But I never saw a dual system failure.
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Curmudgeon
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 4:50 pm

The airline that I know best currently has had approximately 800 plane/years operating 737 aircraft without a dual system loss. (737-3/4/8).
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domokun
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 5:10 pm

Quoting ZANL188 (Thread starter):
According to Alaska Airlines flight safety personnel

... Who, based on this excerpt, either happened to run into an unfortunate but rare failure or who need to pay more attention.

Quoting ZANL188 (Thread starter):
the hydraulic failure of System B (the first event) was attributed to a catastrophic failure of the engine driven hydraulic pump. ASA maintenance personnel found a spoiler hydraulic line that had fractured and bled out the System A (the second event) hydraulic quantity leading to the dual hydraulic failure event.
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 5:36 pm

Quoting ZANL188 (Thread starter):
Just curious how often dual hydraulic failures (& use of the mechanical reversion) occur on 737s specifically & on other large jets in general.

Thanks

http://www.ntsb.gov/ntsb/brief.asp?e...key=1

Alaska Airlines, what a surprise. We all know how great their maintenance inspections are.

But yes, they are extremely rare. The only complete hydraulic losses I can think of are JAL 123 and UA 232. You know the outcomes there. File that under worst case scenario along with inflight break up and inflight thrust reverser deployment.
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Mir
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 6:15 pm

5 people on the plane? I take it this was a positioning flight then? Or was it that five people on board suffered very minor injuries?

-Mir
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HAWK21M
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 6:54 pm

Very rare.With Three systems in total There is a safety factor built in.
regds
MEL
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Curmudgeon
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 7:01 pm

There are two systems in total on a 737, plus the stand-by rudder. Manual reversion is provided for roll and pitch, plus the stabiliser electrics. Flight without hydraulics on the 737 is certainly possible, and trained for, as all three axes of control are still available to the crew. The 737 may be unique in having a manual reversion, but I can't speak with authority on that.
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zanl188
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 8:57 pm

Quoting Mir (Reply 5):
5 people on the plane? I take it this was a positioning flight then? Or was it that five people on board suffered very minor injuries?

Editting on NTSB preliminary reports leaves something to be desired. "5 uninjured" yet it's a "... scheduled international passenger flight...".

And what time did it arrrive in LA?

"...On October 19, 2006, about 0100 Pacific daylight time, a Boeing 737-790, N614AS, returned to Los Angeles International Airport (LAX..."

"...however, the flight crew was able to land the airplane without further incident at 0330. ..."

Did it hold in the LAX area for 2.5 hours?

Back on topic... Is either a catastrophic pump failure or a line fracture something that MX ought to be able to uncover in advance?
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Curmudgeon
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 9:11 pm

Quoting ZANL188 (Reply 8):
Back on topic... Is either a catastrophic pump failure or a line fracture something that MX ought to be able to uncover in advance

Probably not. Hydraulic pump parameters are not recorded by any telemetry on the aircraft, nor are lines-it just wouldn't be feasible. Also, lines fracture without much warning, as can mechanical (or electric) pumps.
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DC8FriendShip
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RE: 737 Dual Hydraulic Failure - Frequency?

Sun Nov 19, 2006 11:04 pm

Quoting TrijetsRMissed (Reply 4):
The only complete hydraulic losses I can think of are JAL 123 and UA 232. You know the outcomes there

The aircraft above had complete hydraulic loss. The fact that it had manual reversion kept the aircraft controllable. UA 232 had triple hydraulics- a very safe system indeed. The fact that no SB's or AD's came of that accident shows that it is a one in a millon event.

Quoting Curmudgeon (Reply 7):
The 737 may be unique in having a manual reversion, but I can't speak with authority on that.

Manual reversion was commonly used before hydraulically boosted controls to move large flight controls. the operator actally moves the tab, which moves in the Opposite direction from the actual control. this being why it is called reversion.
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OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 2:56 am

Quoting ZANL188 (Thread starter):
Just curious how often dual hydraulic failures (& use of the mechanical reversion) occur on 737s specifically & on other large jets in general.

Can't speak for other types, but in 35 years of 737 flying at my place, I know of only one A and B system failure. The crew used manual reversion and the standby rudder (hydraulic) system and landed without incident.

Quoting Domokun (Reply 3):
... Who, based on this excerpt, either happened to run into an unfortunate but rare failure or who need to pay more attention.

...rare failure.

Quoting TrijetsRMissed (Reply 4):
Alaska Airlines, what a surprise. We all know how great their maintenance inspections are.

Cheap shot...

Quoting TrijetsRMissed (Reply 4):
The only complete hydraulic losses I can think of are JAL 123 and UA 232. You know the outcomes there.

While those two were total system failures, they had no manual reversion systems as the 737 does. It's an apples-to-oranges comparison.

Quoting DC8FriendShip (Reply 10):
the operator actally moves the tab, which moves in the Opposite direction from the actual control. this being why it is called reversion.

It sounds like you're describing how the trim tabs work...

I was always under impression that the word "reversion" in term "manual reversion" was a form of the word "revert" as in reverting from one type of system (hydraulic) to another one (cables) that was of an older design. Check out the 3rd definition at:

http://dictionary.reference.com/browse/reversion
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DC8FriendShip
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 4:13 am

Why not look in an aeronautic dictionary?

Manaul reversion uses servo tabs on the flight controls, which in response to the control wheel inputs, move in the opposite direction of the intended movement of the flight control. Trim tabs work in the same way, but are not connected to the control columns. try this little test http://www.sheffield.com/FAAKT/Aircraftaerodynamics1.html
see how many you get right it will help you see how much knowledge you have.  Smile
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Curmudgeon
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 6:34 am

Quoting DC8FriendShip (Reply 12):
try this little test http://www.sheffield.com/FAAKT/Aircraftaerodynamics1.html
see how many you get right it will help you see how much knowledge you have.

After a brief look, I think that's a crappy little test. The answers given are incomplete, and the page design is primitive. I've never seen a complete explanation of anything aerodynamic that can be distilled into a three choice answer. I wouldn't hang my understanding of "manual reversion" on this test.

The 737 elevator is flown manually via the tab, but in practise it has such a huge dead band, and is so heavy, electric stabiliser trimming is done concurrently to lighten the load.

The current Boeing FCOM does not inform the pilot on the aerodynamic features employed on the control surfaces at all. Having had 737 training at a few places now, including Boeing, everybody uses the phrase "manual reversion" in the sense that you have reverted to "pre-powered flight control" methods to control the flight path, without mentioning, or caring, exactly how it is accomplished.
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OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 6:40 am

Quoting Curmudgeon (Reply 13):
The current Boeing FCOM does not inform the pilot on the aerodynamic features employed on the control surfaces at all. Having had 737 training at a few places now, including Boeing, everybody uses the phrase "manual reversion" in the sense that you have reverted to "pre-powered flight control" methods to control the flight path, without mentioning, or caring, exactly how it is accomplished.

Nicely stated...
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miamiair
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 6:53 am

Quoting TrijetsRMissed (Reply 4):
Alaska Airlines, what a surprise. We all know how great their maintenance inspections are.

 redflag 

When was the last time you were there?
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TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 12:10 pm

Quoting OPNLguy (Reply 11):
Quoting TrijetsRMissed (Reply 4):
Alaska Airlines, what a surprise. We all know how great their maintenance inspections are.

Cheap shot...

Facts are facts. What next, are you going to tell me Aeroflot has a great safety record too?

Quoting Miamiair (Reply 15):
When was the last time you were there?

When maintenance personnel are whistle blowing regarding inspection practices what does that tell you? I think that speaks for itself. And that doesn't even include the mess the NTSB uncovered.
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OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 12:45 pm

Quoting TrijetsRMissed (Reply 16):
Facts are facts.

True, facts are facts, but you've taken then so far out of context so as to paint any maintenance-related issue as product of some nefarious intent or conspiracy.

And, no, I don't work for them...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 12:53 pm

Quoting OPNLguy (Reply 17):
True, facts are facts, but you've taken then so far out of context so as to paint any maintenance-related issue as product of some nefarious intent or conspiracy.

No not conspiracy, more in the realm of cost cutting and negligence. The forging of inspections and repairs that never occurred is not a conspiracy theory.
There's nothing quite like a trijet.
 
OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 1:27 pm

Quoting TrijetsRMissed (Reply 18):
No not conspiracy, more in the realm of cost cutting and negligence. The forging of inspections and repairs that never occurred is not a conspiracy theory.

Are you suggesting that the 737 involved had two separate components fail due to "cost cutting and negligence"? If you can't offer any proof of that kind of assertion, I'd submit that you're projecting the AS261-era stuff on the present day, which is quite an assumption...

I'd fly Alaska any day of the week....
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 1:47 pm

Quoting OPNLguy (Reply 19):
Are you suggesting that the 737 involved had two separate components fail due to "cost cutting and negligence"? If you can't offer any proof of that kind of assertion, I'd submit that you're projecting the AS261-era stuff on the present day, which is quite an assumption...

I'd fly Alaska any day of the week....

No I'm not suggesting that, all I am saying is I am never surprised when I hear an AS aircraft have some sort of system malfunction.

I admit I am somewhat biased, but when I interned at the NTSB not one person had a positive thing to say about AS.
There's nothing quite like a trijet.
 
OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 1:59 pm

Quoting TrijetsRMissed (Reply 20):
No I'm not suggesting that, all I am saying is I am never surprised when I hear an AS aircraft have some sort of system malfunction.

I admit I am somewhat biased, but when I interned at the NTSB not one person had a positive thing to say about AS.

There's an old saying that goes "Never attribute to malice that which can be adequately explained by stupidity..."

Modifying that here a bit to fit the situation, it'd be "Never necessarily attribute an airline's past problem(s) to those mechanical situations than can and do happen to every airline flying at one point or another...

'Nuff said...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 2:17 pm

Quoting OPNLguy (Reply 21):
Modifying that here a bit to fit the situation, it'd be "Never necessarily attribute an airline's past problem(s) to those mechanical situations than can and do happen to every airline flying at one point or another...

When you examine the details there is a large difference in say UA 232 vs AS 261. Yes both accidents were caused by system malfunctions, however one was completely avoidable and should have never happened and the other was something no one ever expected would happen. They may be in the same category but hardly alike.

Quoting OPNLguy (Reply 21):
'Nuff said...

No there's a lot more to it than that. You'd learn a lot talking to an NTSB accident investigator.
There's nothing quite like a trijet.
 
OPNLguy
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 3:20 pm

Quoting TrijetsRMissed (Reply 22):
No there's a lot more to it than that. You'd learn a lot talking to an NTSB accident investigator.

In my 25+ years in the biz with 3 different airlines, I've spoken with several, and have indeed learned alot from them as well as various accidents related to my specialty.

Can't say as much for any of their interns as I've never met any...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
miamiair
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 6:54 pm

Quoting TrijetsRMissed (Reply 16):
When maintenance personnel are whistle blowing regarding inspection practices what does that tell you? I think that speaks for itself. And that doesn't even include the mess the NTSB uncovered.

Didn't answer my question. AS MX has cleaned up their act, and your comments are  redflag .

Quoting TrijetsRMissed (Reply 20):
I admit I am somewhat biased,

Enough said.

AS MX got the bad rap, but there are many MX professionals there that you are painting in a bad light with your broad brush.
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HAWK21M
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RE: 737 Dual Hydraulic Failure - Frequency?

Mon Nov 20, 2006 10:54 pm

Quoting TrijetsRMissed (Reply 22):
You'd learn a lot talking to an NTSB accident investigator

Pls Elaborate.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Wed Nov 22, 2006 8:32 am

Quoting HAWK21M (Reply 25):
Quoting TrijetsRMissed (Reply 22):
You'd learn a lot talking to an NTSB accident investigator

Pls Elaborate.
regds
MEL

Certain airlines and aircraft have a history of problems, whether fatal or not. While the NTSB may not publicly acknowledge this, they do keep a closer eye on some airlines compared to others. Also while many accidents can be classified in the same category, for exampe system malfunction there could be several different causes which have nothing in common with one another from accident to accident. Nothing is simply "nuff said"

Quoting OPNLguy (Reply 23):
In my 25+ years in the biz with 3 different airlines, I've spoken with several, and have indeed learned alot from them as well as various accidents related to my specialty.

Well given by your comments you must have been speaking more than listening..

Quoting OPNLguy (Reply 23):
Can't say as much for any of their interns as I've never met any...

Haha good one, and you're accusing me of cheap shots? It's not worth arguing facts with opinions.

Quoting Miamiair (Reply 24):
Didn't answer my question. AS MX has cleaned up their act, and your comments are .

Do you want me to spell it out or draw a picture? You seem to know at least a little bit about AS mx history. By the way, do you work for AS?
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miamiair
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RE: 737 Dual Hydraulic Failure - Frequency?

Wed Nov 22, 2006 8:53 pm

Quoting TrijetsRMissed (Reply 26):

Just a friendly note:

Whether or not you are still employed by the NTSB, your arrogance is noted. The NTSB investigators I have dealt with are a fine lot. Your tenure as an intern does not qualify you to tell some of the people here that they speak more than listen. Many people here have probably forgotten more about aviation maintenance,than you have learned. The opinions you are offering, are exactly that, not facts.
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HAWK21M
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RE: 737 Dual Hydraulic Failure - Frequency?

Thu Nov 23, 2006 1:02 am

Quoting TrijetsRMissed (Reply 26):
Certain airlines and aircraft have a history of problems, whether fatal or not. While the NTSB may not publicly acknowledge this, they do keep a closer eye on some airlines compared to others.

Don't they provide Info to reach those Airlines thru the Regulatory Authorities.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
TrijetsRMissed
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RE: 737 Dual Hydraulic Failure - Frequency?

Thu Nov 23, 2006 12:46 pm

Quoting Miamiair (Reply 27):
Just a friendly note:

You don't have to agree with everything I say and visa versa, its an open forum for debate. You think I'm arrogant, I think you're ignorant. I do think it is worth noting that casual conversations with an NTSB personnel are not comparable to on the job training and learning the ropes with those in the know at the safety board. We will just have to agree to disagree on this one.  smirk 
There's nothing quite like a trijet.
 
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HAWK21M
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RE: 737 Dual Hydraulic Failure - Frequency?

Thu Nov 23, 2006 5:48 pm

Quoting TrijetsRMissed (Reply 29):
You think I'm arrogant, I think you're ignorant

My side of the story,Your side of the story & the Truth.
Lets stick to the topic folks.Its better that way.
Any data on the number of Multiple Hyd failures on a B737 till date.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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