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Controlling Airbus A320 With Total Hydraulic Loss  
User currently offlinedhawald3 From India, joined Jun 2011, 17 posts, RR: 0
Posted (3 years 6 months 3 days 14 hours ago) and read 21227 times:

In an Airbus A320 the Rudder and the THS have mechanical cable connections for their operation, but these cables run only till the hydraulic servos that in turn move these surfaces with the help of hydraulic pressure.

I was wondering how will the aircraft be controlled if there is loss of all the three hydraulic systems.

as far as I know the Boeing 737 can be controlled even without Hydraulics.

30 replies: All unread, showing first 25:
 
User currently offlinelonghauler From Canada, joined Mar 2004, 5164 posts, RR: 43
Reply 1, posted (3 years 6 months 3 days 13 hours ago) and read 21245 times:

Quoting dhawald3 (Thread starter):
I was wondering how will the aircraft be controlled if there is loss of all the three hydraulic systems.

This is no different from any large transport aircraft designed from the B747 onward. The short answer is no, the flight controls can not be controlled without hydraulic power. To date, in the last 50 years, I can think of only two occurances where that has happened. The JAL B747 out of Tokyo and the UAL DC-10 into Sioux City.

Quoting dhawald3 (Thread starter):
as far as I know the Boeing 737 can be controlled even without Hydraulics.

Manual reversion is a "feature" of all old Boeing aircraft designs including the B737, B727 and the B707.



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlinebj87 From Netherlands, joined Jun 2009, 448 posts, RR: 0
Reply 2, posted (3 years 6 months 3 days 12 hours ago) and read 21213 times:

Quoting longhauler (Reply 1):
, I can think of only two occurances

There is also the DHL A300 that got hit by a ground to air missile in Iraq and lost all hydraulics. The crew actually managed to land it only to come to a halt in a mine field!

They used the planes engines to steer and climb/decent, amazing airmanship.

Link to wiki for the complete story: http://en.wikipedia.org/wiki/2003_Ba...d_DHL_attempted_shootdown_incident

There was also an Air Crash Investigation episode about the incident. Very interesting.

The story should be the same for an A320.

A couple of years back there was even a study/project where they installed a computer system on aircraft that has the capability to steer the plane only using the engines while the pilot still use the joystick/side stick for input controls. I believe the conclusion was that it was achievable but very expensive to build and certify for every plane hence it is not a feature on any plane that I know of.

(I am not sure about this but I believe it was NASA that did the study and actually performed several landings in a real plane using the system. I think I saw this subject on TV somewhere but can't remember the program. It might have been the ACI episode.)

Some pics of the DHL A300

Damage to the wing:

http://upload.wikimedia.org/wikipedia/commons/1/15/DHL_Airbus_A300B4-203F%2C_BIAP.jpg

The place they ended up, the mine field!

http://upload.wikimedia.org/wikipedia/commons/3/35/DHL_Airbus_A300B4-203F%2C_BIAP_7.jpg

Edit: added pictures



[Edited 2011-06-28 10:18:31]

User currently offlinesccutler From United States of America, joined Jan 2000, 5618 posts, RR: 28
Reply 3, posted (3 years 6 months 3 days 12 hours ago) and read 21185 times:

While I may prefer the Boeing standard for flight control logic, the redundancy built into the Airbii is more than sufficient; there are so many more areas of potential failure that would merit concern, long before worrying about what happens if the series of complete failures necessary to give rise to the OP's scenario.


...three miles from BRONS, clear for the ILS one five approach...
User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 4, posted (3 years 6 months 3 days 11 hours ago) and read 21137 times:

I reckon you imply that not even the Blue pump which is either pressurized electrically or by the RAT is functioning. Well, in that event, I believe there is no way of controlling any flight control surfaces. Although not a loss of all HYD servos, this video shows a simulated loss of Green + Yellow systems with only the Blue system remaining.

http://www.youtube.com/watch?v=6XIn1YGT8pw&feature=related

Speedbird741

[Edited 2011-06-28 11:31:22]


Boa noite Faro, Air Portugal 257 climbing flight level 340
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6972 posts, RR: 76
Reply 5, posted (3 years 6 months 3 days 9 hours ago) and read 20992 times:

Well, the 737 has manual reversion, but, it's the only Boeing with it in production. Anything after the 737 (ie: 747, 757, 767, 777, 787) has no manual reversion.

The 737 only has 2.5 Hyd Systems (2 primaries, and 1 small backup system, mainly for the rudder which has no manual reversion in the event of a TOTAL Hyd Fail).

The Airbii and the other Boeings in production, has 3 full Hyd sys... 3 HYD sys are there for a reason... redundancy...
If you have a mechanical link with HYD boost (reversible) like the 737, you only need 2 Hyd Sys (the rudder, non-reversible, has 3 HYD systems)

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 6, posted (3 years 6 months 3 days 7 hours ago) and read 20915 times:

Quoting mandala499 (Reply 5):
The Airbii and the other Boeings in production, has 3 full Hyd sys... 3 HYD sys are there for a reason... redundancy...


Did Boeing remove one of the hydraulic system from the 747-8's?


User currently offlinezeke From Hong Kong, joined Dec 2006, 9242 posts, RR: 76
Reply 7, posted (3 years 6 months 3 days 7 hours ago) and read 20900 times:

Quoting dhawald3 (Thread starter):

as far as I know the Boeing 737 can be controlled even without Hydraulics.

And the A380, it has self contained electro hydraulic actuators which are independent of the aircraft hydraulic systems giving it controllability even in the event of the failure of all 3 aircraft hydraulic systems.

Quoting 474218 (Reply 6):

Did Boeing remove one of the hydraulic system from the 747-8's?

Still has 4. Systems 1 and 4 power the trailing edge flaps, landing gear, normal brakes (SYS 4), alternate brakes (SYS 1), steering, and their respective thrust reversers. Systems 1 and 4 also provide redundant power to the primary flight controls. Systems 2 and 3 power the primary flight controls, stabilizer trim, elevator feel, and their respective thrust reversers. System 2 also powers the alternate brakes and lower yaw damper. System 3 powers the upper yaw damper. Systems 1, 2, and 3 power the respective center, right, and left autopilot servos. Systems 2, 3, and 4 power the spoilers.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6972 posts, RR: 76
Reply 8, posted (3 years 6 months 3 days 5 hours ago) and read 20828 times:

Quoting 474218 (Reply 6):
Did Boeing remove one of the hydraulic system from the 747-8's?

Bahhhhhh!!!
I keep forgetting that it has 4 on the 747s!!!! Luckily, we have Zeke to remind me!   

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 9, posted (3 years 6 months 3 days 4 hours ago) and read 20814 times:

Quoting mandala499 (Reply 8):
I keep forgetting that it has 4 on the 747s!!!! Luckily, we have Zeke to remind me!


I knew you knew! But you can't let softball like that go by with taking a big swing!   


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (3 years 6 months 3 days 1 hour ago) and read 20719 times:

Quoting longhauler (Reply 1):
This is no different from any large transport aircraft designed from the B747 onward. The short answer is no, the flight controls can not be controlled without hydraulic power.

As Zeke noted, A380 has EHA's that give you control without hydrauilc system pressure. 787 has something similar. I think the days of no control after full hydraulic failure are gone for new designs.

Tom.


User currently offlineWingscrubber From UK - England, joined Sep 2001, 854 posts, RR: 0
Reply 11, posted (3 years 6 months 3 days ago) and read 20712 times:

Quoting zeke (Reply 7):
And the A380, it has self contained electro hydraulic actuators which are independent of the aircraft hydraulic systems giving it controllability even in the event of the failure of all 3 aircraft hydraulic systems.

A380 only has 2 main hydraulic systems, but each main system has 4 engine driven pumps and 2 electric motor pumps. The the backup EHAs comprise the elements of the phantom 3rd system - they're just at the end of a cable instead of a hydraulic line, though I don't know if they're 100% duty cycle actuators or not.

A320 cannot be controlled with 'total hydraulic loss', as it is pure FBW controlled - no pushrods and bellcranks to allow the pilot to fly the airplane with his strength alone, this is why it must have 3 systems, two primarily engine-driven pump powered and the 3rd is electrically powered. Manual-reversion aircraft are flyable without hydraulics with manual input alone, but this can be very hard work. For example, the Citation X has this capability and has used it, a X pilot who experienced this described it to me as simply being 'very difficult'.

Manual Reversion Flight Controls... (by JETPILOT Jan 17 2000 in Civil Aviation)

The rationale is that no single failure combined with any probable failure can result in loss of the aircraft, so with three systems you can have a single or dual engine failure and still be flyable, or a leak in any one or two systems.
This is why there has been a number of 3-system airliners, including Boeing 75,6,7, Airbus A319/20/21/30/40, Bombardier CRJ etc

The trend now is to try to get rid of that third system, and substitute in EHAs or Powerpacks.



Resident TechOps Troll
User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 12, posted (3 years 6 months 2 days 22 hours ago) and read 20656 times:

Quoting zeke (Reply 7):
And the A380, it has self contained electro hydraulic actuators which are independent of the aircraft hydraulic systems giving it controllability even in the event of the failure of all 3 aircraft hydraulic systems.

I think it's interesting that these systems were knocked out in the QF32 incident, and the plane was only controllable because one of the hydraulic systems remained functional. I was expecting the EHAs to be more robust than the hydraulics. Bad luck, or are the EHA's more about improving economics than improving safety?


User currently offlinezeke From Hong Kong, joined Dec 2006, 9242 posts, RR: 76
Reply 13, posted (3 years 6 months 2 days 21 hours ago) and read 20627 times:

Quoting Wingscrubber (Reply 11):

A380 only has 2 main hydraulic systems, but each main system has 4 engine driven pumps and 2 electric motor pumps.

You are right, I knew it only has yellow and green, and the they dropped the blue (well as your said decentralised it using EHAs).

Quoting Wingscrubber (Reply 11):
The the backup EHAs comprise the elements of the phantom 3rd system - they're just at the end of a cable instead of a hydraulic line, though I don't know if they're 100% duty cycle actuators or not.

The A380 has three different types of actuators, the conventional ones that people would be familiar with on other airliners, Electro-Hydrostatic Actuators (EHAs) which are an electrical backup that are active in case of complete hydraulic failure, and Electrical Backup Hydraulic Actuators (EBHAs) that are a combination of a conventional actuator and an EHA. They work as normal actuators when hydraulics are present, and as an emergency backup when not.

The ailerons and elevator have Electro Hydrostatic Actuators (EHA) and the spoilers and rudder have Electrical Backup Hydraulic Actuators (EBHA).

Quoting thegeek (Reply 12):
I think it's interesting that these systems were knocked out in the QF32 incident, and the plane was only controllable because one of the hydraulic systems remained functional. I was expecting the EHAs to be more robust than the hydraulics.

I am not sure exactly what was knocked out, however the flight controls have power sources from the green and yellow hydraulic systems, the AC bus 1 & 2, and the AS essential bus. Even if the aircraft was totally without any hydraulic power, or electrical power except for the essential bus, it still has ailerons, elevator and rudder control. The flight controls were actually designed with an engine burst in mind.

Quoting thegeek (Reply 12):
Bad luck, or are the EHA's more about improving economics than improving safety?

Both, economics are improved as weight and system complexity is reduced, safety is improved as additional redundancy is provided and the systems are simpler, hence less to go wrong.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (3 years 6 months 2 days 16 hours ago) and read 20554 times:

Quoting Wingscrubber (Reply 11):
A320 cannot be controlled with 'total hydraulic loss', as it is pure FBW controlled

Those two statements don't go together. Being FBW has nothing to do with which actuation technology you're using. The JSF is all, or nearly all, EHA actuated (it has no hydraulic system in the conventional sense) yet is pure FBW. There is no technical reason you can't build a steel-cable-pulley-crank actuation system on top of a FBW controller, although I'm not aware that anyone has done it.

Quoting thegeek (Reply 12):
I think it's interesting that these systems were knocked out in the QF32 incident, and the plane was only controllable because one of the hydraulic systems remained functional. I was expecting the EHAs to be more robust than the hydraulics. Bad luck, or are the EHA's more about improving economics than improving safety?

Incredibly bad luck...QF32 had a couple of "magic fragments" that severed both legs of a redundant electrical system. This is how they lost control of the engine spar valves too.

Tom.


User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 15, posted (3 years 6 months 2 days 8 hours ago) and read 20433 times:

Quoting zeke (Reply 13):
I am not sure exactly what was knocked out, however the flight controls have power sources from the green and yellow hydraulic systems, the AC bus 1 & 2, and the AS essential bus.

AC 1&2 and a hydraulic system were knocked out AIUI. I think they still had one hydraulic system and I guess "the AS essential bus". Which meant a number of spoilers were inoperative, and I think some of the ailerons. But still enough remained to get back on the ground.


User currently offlineWingscrubber From UK - England, joined Sep 2001, 854 posts, RR: 0
Reply 16, posted (3 years 6 months 2 days ago) and read 20303 times:

Quoting tdscanuck (Reply 14):
Being FBW has nothing to do with which actuation technology you're using.

FBW generally implies the use of electronically controlled servo-actuators instead of pushrod-controlled actuators, as is the case with the A320 - there is no mechanical link between the sidestick and the control surface, so if all three hydraulic systems are down, no sidestick waggling will help. Those statements do go together with respect to the A320(thread topic) because it has no EHAs.

Another failure mode is the case where the electronic input(which is probably dual redundant) to the actuator fails. To fly the A320 you need hydraulic power and electronic control, if you lose either one, you have lost that control surface, unless a secondary or tertiary actuator on the same control surface is still functional.

If the actuator is controlled mechanically, even if the mechanical input comes from a computer, it is not a true fly-by-wire actuator. If you consider any airplane with electric-mechanical input to the control surface to be fly-by-wire, then a Cessna 172 with autopilot is fly-by-wire.

[Edited 2011-06-29 22:49:06]


Resident TechOps Troll
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 17, posted (3 years 6 months 1 day 16 hours ago) and read 20170 times:

Quoting Wingscrubber (Reply 16):
FBW generally implies the use of electronically controlled servo-actuators instead of pushrod-controlled actuators

Agreed. But nobody said they had to be hydraulic actuators. You can have pneumatic, electric, electro-hydrostatic, etc. There's also nothing wrong with having a pushrod (or cable) controlled actuator where the other end of the pushrod has some kind of actuator, rather than direct coupling to the pilot inceptors (yoke/stick, column, pedals).

Quoting Wingscrubber (Reply 16):
there is no mechanical link between the sidestick and the control surface, so if all three hydraulic systems are down, no sidestick waggling will help.

In the specific case of the A320, yes, absolutely. And I do acknowledge that the OP was about the A320 specifically. But this statement:

Quoting Wingscrubber (Reply 11):
A320 cannot be controlled with 'total hydraulic loss', as it is pure FBW controlled

Implies that it can't be controlled *because* it's pure FBW. That's not the issue. It can't be controlled with full hydraulic loss because it doesn't have any non-hydraulic actuators, which has nothing to do with whether it's FBW or not.

Quoting Wingscrubber (Reply 16):
If the actuator is controlled mechanically, even if the mechanical input comes from a computer, it is not a true fly-by-wire actuator.

Agreed. But if the actuator is pneumatic, or electric, or an EHA, it's can still be true FBW and be fully functional in the event of a total hydraulic failure.

Quoting Wingscrubber (Reply 16):
If you consider any airplane with electric-mechanical input to the control surface to be fly-by-wire, then a Cessna 172 with autopilot is fly-by-wire.

I wouldn't characterize it in that way. In the case of electro-mechanical input to a purely mechanical flight control system, the electro-mechanical input is replacing the *pilot* actuation, not the control surface actuation. The key to FBW is that there is no mechanical link between the pilot inceptors and the control surfaces...positions are read by sensors that drive some type of computer (analog or digital) that then commands the surfaces. The actual power source to the actuators is not relevant to whether it's a FBW aircraft.

Tom.


User currently offlinejetlagged From United Kingdom, joined Jan 2005, 2577 posts, RR: 25
Reply 18, posted (3 years 6 months 1 day 14 hours ago) and read 20132 times:

Quoting tdscanuck (Reply 17):
Implies that it can't be controlled *because* it's pure FBW. That's not the issue. It can't be controlled with full hydraulic loss because it doesn't have any non-hydraulic actuators, which has nothing to do with whether it's FBW or not.

I understood Wingscrubber's comment to mean that in the case of FBW there can be no mechanical back up in the event of a flight control system power failure as no mechanical linkages exist.

Quoting tdscanuck (Reply 17):
Agreed. But if the actuator is pneumatic, or electric, or an EHA, it's can still be true FBW and be fully functional in the event of a total hydraulic failure.

Clearly an electric, pneumatic or EHA flight control servo would not be affected by loss of hydraulic power. Surely the generalised question, beyond the specific A320 case in the OP, is "can the flight control servo be operated without its power source?" In other words is there any back up mode?



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlinedhawald3 From India, joined Jun 2011, 17 posts, RR: 0
Reply 19, posted (3 years 6 months 1 day 12 hours ago) and read 20073 times:

Here are the flight controls of A320 along with the computer priorities for the redundancies.



User currently offlinetravelavnut From Netherlands, joined May 2010, 1670 posts, RR: 7
Reply 20, posted (3 years 6 months 1 day 12 hours ago) and read 20068 times:

Quoting dhawald3 (Reply 19):

Nice diagram, thanks for sharing!

Really shows the levels of redundancies in airliners.



Live From Amsterdam!
User currently offlinedhawald3 From India, joined Jun 2011, 17 posts, RR: 0
Reply 21, posted (3 years 6 months 1 day 11 hours ago) and read 20039 times:

Quoting travelavnut (Reply 20):
Really shows the levels of redundancies in airliners.

Forgot to mention the diagram also shows the control of flight surfaces through multiple hydraulic supply using the three systems in Airbus A320 Green, Blue, Yellow

[Edited 2011-06-30 11:59:17]

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 22, posted (3 years 6 months 16 hours ago) and read 19837 times:

Quoting jetlagged (Reply 18):
I understood Wingscrubber's comment to mean that in the case of FBW there can be no mechanical back up in the event of a flight control system power failure as no mechanical linkages exist.

Ah...OK, that's a different interpretation than I had. Not sure which was the correct one.

However, if we go with that definition, do we not consider the 777 to be full FBW? It has mechanical links to some of the spoilers.

Tom.


User currently offlinejetlagged From United Kingdom, joined Jan 2005, 2577 posts, RR: 25
Reply 23, posted (3 years 6 months 15 hours ago) and read 19823 times:

Quoting tdscanuck (Reply 22):
However, if we go with that definition, do we not consider the 777 to be full FBW? It has mechanical links to some of the spoilers

Now we're into hair splitting territory. I didn't propose that as a dictionary definition of FBW. The A320 is not "full" FBW by that definition either.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineashyy From United Kingdom, joined Sep 2010, 12 posts, RR: 0
Reply 24, posted (3 years 5 months 3 weeks 6 days 19 hours ago) and read 19503 times:

Quoting tdscanuck (Reply 14):

I would say good luck, the fact that the aircraft landed safely and without major damage means the entire hydraulic system design served it's purpose despite extensive damage to the wing following a catastrophic failure that should never of happened.

An uncontained engine failure is a very serious issue, engine manufacturers test for it rigourously and cannot pass an engine into service until it can contain such a violent and high energy failure. There is no predicting what damage that engine could of done to the surrounding wing or worst penetrated the fuel tanks. As the aircraft landed safely and relatively uneventfully considering what happened it's a triumph in the aircraft's design.

It could very easily of been a very different story, UA232 serves as a very real example of the dangers of uncontained engine failures.

[Edited 2011-07-04 03:55:58]

25 flipdewaf : You only have to contain the fan, you arent expected to contain a turbine blade, just minimise the risk if it does go bang. Fred
26 David L : I thought a shed turbine blade was supposed to be contained. What isn't required to be contained is an entire disc that has shattered into three extr
27 474218 : The turbine blades should be contained, broken/failed bits should exit through back of the engine, if they exit at all. However, uncontrolled failure
28 navion1217 : Is the THS hydraulically or electrically actuated?
29 Speedbird741 : It is hydraulically actuated and controlled either mechanically or electrically. However, mechanical control has priority over electrical. Speedbird7
30 flipdewaf : When we were designing an aircraft at uni(I nkow its not the real thing) we were taught that there had to be a less than 20% chance that the burst di
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