complete hydraulic failure
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complete hydraulic failure
dear all
i was watching flightline, a programme on discovery and they were talking about a pilots worst nightmare being complete hydralic failure.
They reffered to some accident that occured in the late eightes in USA but i was more interested in the technology that NASA are looking into whereby pilots can land the a/c using engine thrust alone.
Does anyone have any more information about this and has anyone ever experienced hydraulic failure and what are the procedures in those circumstances.
Thanks.
i was watching flightline, a programme on discovery and they were talking about a pilots worst nightmare being complete hydralic failure.
They reffered to some accident that occured in the late eightes in USA but i was more interested in the technology that NASA are looking into whereby pilots can land the a/c using engine thrust alone.
Does anyone have any more information about this and has anyone ever experienced hydraulic failure and what are the procedures in those circumstances.
Thanks.
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I presume they mean the Sioux City DC10 which didn't have much more than power levers left to control it with.
And yes, I have had complete hydraulic failure and still managed to land without incident, but as it was on a Cessna 120 the only hydraulics were the toe-brakes.
And yes, I have had complete hydraulic failure and still managed to land without incident, but as it was on a Cessna 120 the only hydraulics were the toe-brakes.
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I believe the accident you are refering to was at Sioux City. DC10 had an uncontained engine failure - the debris ripped all three hydraulic systems, causing all the fluid to leak out. Since the hydraulics power the flight controls....
The aircraft was "landed" using assymetric thrust from #1 & #3 engines. Unfortunately flipped over on landing. Many dead but on the other hand, many survived. Crew highly praised, since this was supposed to be impossible (This led to a re-design of the hydraulic line routings).
Since then NASA and others have been investigating using #1 & #3 for yaw control, #2 for pitch control. I seem to remember they landed an MD11 (or DC10) successfully using this method.
I'm sure others can fill in more details. Hope of some use.
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rgds Rat
The aircraft was "landed" using assymetric thrust from #1 & #3 engines. Unfortunately flipped over on landing. Many dead but on the other hand, many survived. Crew highly praised, since this was supposed to be impossible (This led to a re-design of the hydraulic line routings).
Since then NASA and others have been investigating using #1 & #3 for yaw control, #2 for pitch control. I seem to remember they landed an MD11 (or DC10) successfully using this method.
I'm sure others can fill in more details. Hope of some use.
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rgds Rat
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the impact of a complete hydraulic failure depends on the aircraft design and what you mean by "complete"
In a fairly simple aircraft (a C-150 for example) the only thing hydraulic is the brakes and given enough runway (maybe some nice grass) you can land it fine without the hydraulics. When you have hydraulicly powered flight controls (as in the DC-10) normal practice is to have redundent systems (at least 3) with 2 of them running to each control. this makes the probability of a "complete" hydraulic failure a lot less but as the examples cited show not impossible by any means.
Hydraulics, because of the force needed and weight and economic considerations are generally the way flight controls on decently complex aircraft are powered. Military aircraft using fly by wire still use hydraulics for the power of the flight controls but they use high pressure low volume systems. Some of the NASA work I have heard of would use bleed air from the engines for control purposes, kind of like the nozzles on a Harrier. I suppose with enough bellcranks, gears, and bicycle chains this could work but how often do nozzles jam or go out of rig? Maybe as often as hydraulic s fail? I don't know.
My last hydraulic failure was in an A-7E which has three hydraulic systems for flight controls and one for utility systems like landing gear and speed brakes and wheel brakes. since these systems are all linked to the engine (and RAT) for pressure and the utility system has a tendency to lose fluid there is a valve in the cockpit to isolate the utility systems so you don't pee all your fluid over the side. when you come into the break you then use a nitrogen gas bottle to blow the gear and hook down and do a short field arrested landing. Now all airliners need is a tail hook and the airports some arresting gear.
In a fairly simple aircraft (a C-150 for example) the only thing hydraulic is the brakes and given enough runway (maybe some nice grass) you can land it fine without the hydraulics. When you have hydraulicly powered flight controls (as in the DC-10) normal practice is to have redundent systems (at least 3) with 2 of them running to each control. this makes the probability of a "complete" hydraulic failure a lot less but as the examples cited show not impossible by any means.
Hydraulics, because of the force needed and weight and economic considerations are generally the way flight controls on decently complex aircraft are powered. Military aircraft using fly by wire still use hydraulics for the power of the flight controls but they use high pressure low volume systems. Some of the NASA work I have heard of would use bleed air from the engines for control purposes, kind of like the nozzles on a Harrier. I suppose with enough bellcranks, gears, and bicycle chains this could work but how often do nozzles jam or go out of rig? Maybe as often as hydraulic s fail? I don't know.
My last hydraulic failure was in an A-7E which has three hydraulic systems for flight controls and one for utility systems like landing gear and speed brakes and wheel brakes. since these systems are all linked to the engine (and RAT) for pressure and the utility system has a tendency to lose fluid there is a valve in the cockpit to isolate the utility systems so you don't pee all your fluid over the side. when you come into the break you then use a nitrogen gas bottle to blow the gear and hook down and do a short field arrested landing. Now all airliners need is a tail hook and the airports some arresting gear.
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For a historical perspetive:
The DC8 has a single main system of hydraulics powering the alirons, rudder, stabulator trim(the elevators are manually powered by the musles of the flight crew). Flight spoilers are powered by a separate electric hydraulic pump drawing fluid from a separate hydrualic resevoir. Sub systems off the main hydraulic system include landing gear, brakes, flaps, slots, nose wheel steering, ect.
In the event of a total hydraulic fluid loss, all systems are isolated from the cockpit. Flaps are lowered by remaining fluid and main electric hydraulic pump. Landing gear free falls and down locks are operated by a separate resevoir and the main electric pump. Also the slots are opened by this same system. Alerons are now operated manually by movement of the flying tabs. Stab trim is operated by an electical motor back-up system(the auto-pilot uses the same system to trim the stab normally). Rudder can be operated manually, but has a separate electric hydraulic pump and resevoir. Brakes are pressurized by air pressure.
So with fluid loss you have really lost nothing important. The airplane fairly easy to fly under the situation.
Ray
The DC8 has a single main system of hydraulics powering the alirons, rudder, stabulator trim(the elevators are manually powered by the musles of the flight crew). Flight spoilers are powered by a separate electric hydraulic pump drawing fluid from a separate hydrualic resevoir. Sub systems off the main hydraulic system include landing gear, brakes, flaps, slots, nose wheel steering, ect.
In the event of a total hydraulic fluid loss, all systems are isolated from the cockpit. Flaps are lowered by remaining fluid and main electric hydraulic pump. Landing gear free falls and down locks are operated by a separate resevoir and the main electric pump. Also the slots are opened by this same system. Alerons are now operated manually by movement of the flying tabs. Stab trim is operated by an electical motor back-up system(the auto-pilot uses the same system to trim the stab normally). Rudder can be operated manually, but has a separate electric hydraulic pump and resevoir. Brakes are pressurized by air pressure.
So with fluid loss you have really lost nothing important. The airplane fairly easy to fly under the situation.
Ray
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On the DC10, following the Sioux city incident, the hyds were not redesigned, but additional fuses fitted at the tail to prevent total fluid loss if lines were damaged in this region due to uncontained engine failure. As another measure, system 3 was to hold more than the usual amount of fluid.
Regds
Regds
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I think, what Purple Haze refered to and NASA was looking into, is thrust vectoring.
It is only used on fighters, like the F22 and Su27 (if I remember correctly), and will probably not see it way to civilian a/c. The purpose to use it on military a/c is to improve the maneuvering capability and not as a backup system.
It is only used on fighters, like the F22 and Su27 (if I remember correctly), and will probably not see it way to civilian a/c. The purpose to use it on military a/c is to improve the maneuvering capability and not as a backup system.
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Had hydraulic fuses been fitted to the DC-10 and the 747 the accident in Iowa might not have happened or, possibly not have been so bad. It would also have saved the 747 in Japan that suffereed the loss of all three hydraulic systems due to failure of the pressure bulk head. In that incident the vertical fin was blown off but that in itself is survivable.
I don't know if fuses were even considered in the design of both aircraft but based on my experience if it were recommended by the reliability engineer the safety engineer would counter the reliability engineer by saying that they had not concieved of any failure that would cause loss of all three systems. On the other hand if they were considered, the management would offer the same argument used by the safety engineers and would add that it would add weight and cost. General electric proved through the use of Boolean Algebra that the fan disc had a projected probability of failure of 1 10-9 or greater. It is not known if the reliability engineer had consiered a faulty manufacturing process as a mode of failure. It was later proved that there was sand entrapped in the fan disc as a result of a faulty manufacturing process. Since GE stated in their safety analysis that the probility of failure was so low then Douglas never felt it was necessary to protect the elements of the hydraulic systems in the vicinity of No. 2 engine. A similar failure caused the loss of a 737 in Manchester and the failure resulted because the engine manufacturer (P&W) said the engine would never fail in the manner that it did and no precautions were taken by Boeing to protect the underwing. Think Concorde!
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The Cat
[This message has been edited by Lu Zuckerman (edited 05 January 2001).]
I don't know if fuses were even considered in the design of both aircraft but based on my experience if it were recommended by the reliability engineer the safety engineer would counter the reliability engineer by saying that they had not concieved of any failure that would cause loss of all three systems. On the other hand if they were considered, the management would offer the same argument used by the safety engineers and would add that it would add weight and cost. General electric proved through the use of Boolean Algebra that the fan disc had a projected probability of failure of 1 10-9 or greater. It is not known if the reliability engineer had consiered a faulty manufacturing process as a mode of failure. It was later proved that there was sand entrapped in the fan disc as a result of a faulty manufacturing process. Since GE stated in their safety analysis that the probility of failure was so low then Douglas never felt it was necessary to protect the elements of the hydraulic systems in the vicinity of No. 2 engine. A similar failure caused the loss of a 737 in Manchester and the failure resulted because the engine manufacturer (P&W) said the engine would never fail in the manner that it did and no precautions were taken by Boeing to protect the underwing. Think Concorde!
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The Cat
[This message has been edited by Lu Zuckerman (edited 05 January 2001).]
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DC8Ray,
Easy to fly the -8 without hyd? I'd say "flyable", perhaps...
The DC-8 is as big as you can get and still manage to fly it with no hydraulic assist. Larger airplanes proved to be impossible, so other backups have been employed.
The "thrust" only tests were with an MD-11. The higher mounted center engine along with the FBW throttles provided the precision and control authority required to make it work. Of course, if #2 is the one that went and if somehow the hyd s/o valve failed so you ended up in the Sioux City scenario, you wouldn't have #2 to help anyway, so the computer system might not work.
With the valve working it has limited control, a true challenge to get it on the ground still, but possible (at least in the sim!). You have to be ready for the pitch changes as you enter ground effect, among other surprises.
A similar situation happens with either the loss of hydraulic or all electrical on any of the pure FBW aircraft. Of course, in those aircraft there are two separate paths that can land you in the same boat...
Easy to fly the -8 without hyd? I'd say "flyable", perhaps...
The DC-8 is as big as you can get and still manage to fly it with no hydraulic assist. Larger airplanes proved to be impossible, so other backups have been employed.
The "thrust" only tests were with an MD-11. The higher mounted center engine along with the FBW throttles provided the precision and control authority required to make it work. Of course, if #2 is the one that went and if somehow the hyd s/o valve failed so you ended up in the Sioux City scenario, you wouldn't have #2 to help anyway, so the computer system might not work.
With the valve working it has limited control, a true challenge to get it on the ground still, but possible (at least in the sim!). You have to be ready for the pitch changes as you enter ground effect, among other surprises.
A similar situation happens with either the loss of hydraulic or all electrical on any of the pure FBW aircraft. Of course, in those aircraft there are two separate paths that can land you in the same boat...
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Tor, I think that purple haze is not refering to thrust vectoring. Some time ago I read an article in Flight International that NASA was conducting flight tests with a DC 10 (because of obvious advantages from the no. 2 engine position) whereby the flightpath was controlled solely by adjusting thrust on the 3 engines. No flight controls were used. They were able to control the plane using a computer that gave "thrust requests" to the engines using input from the yoke. The idear was to have a backup in case the hydraulics failed.
BTW, 747`s have 4 hydraulic systems. Twice I`ve had one system fail on me (in a 744), but the only implication was a manual gear extension of body and nose gear. Nothing more serious, luckily. Both times the failure was caused by leakage.
I believe the Fokker 27 used to have pneumatically operated flight controls and gear actuating. The advantage being that a leak had less effect on the system.
BTW, 747`s have 4 hydraulic systems. Twice I`ve had one system fail on me (in a 744), but the only implication was a manual gear extension of body and nose gear. Nothing more serious, luckily. Both times the failure was caused by leakage.
I believe the Fokker 27 used to have pneumatically operated flight controls and gear actuating. The advantage being that a leak had less effect on the system.
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thanks for the info, and yes they did mention thrust vectoring and the programme left an impression that one day it might be used in civian aircrafts but it seems unlikely.
But its still fascinating the way we can hopefully land an a/c using thrust from four engines. Is this something u would practice in flight sims today.
from what i remember Captain Eric Moody did a four engine start up in a sim a couple of months before the real thing.
[This message has been edited by purple haze (edited 05 January 2001).]
But its still fascinating the way we can hopefully land an a/c using thrust from four engines. Is this something u would practice in flight sims today.
from what i remember Captain Eric Moody did a four engine start up in a sim a couple of months before the real thing.
[This message has been edited by purple haze (edited 05 January 2001).]
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The 747 classic has a backup control using separate electric drives for the inboard and outboard trailing edge flaps, but it is rarely taught to the pilots and most do not know how to use it. After the Japan accident Boeing offered a fuse for the #4 system but many operators did not do the mod because it costs 110k or so per airplane.
The 744 has the fuse, so it should not suffer the same complete failure. Dunno about the 777.
The 744 has the fuse, so it should not suffer the same complete failure. Dunno about the 777.
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If the dear old VC10 sufferes a total hydraulic failure, you lose flaps, slats, spoilers, tail trim, brakes (except for whatever is left in the accumulators) and nosewheel steering. But you can free-fall the landing gear, make an approach at Vat + 45 and hope that you know where the longest runways are...(LHR and FRA in Europe!!). It has been done in the past, I believe, when one of the re-possessed EACC Super VC10s landed at Filton with no hydraulics.
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To: askcv
$110,000.00? You have to be kidding. How much does it cost to cut out a small section of hydraulic tubing and prepare the ends by flaring and then insert the fuse? Oh, I completely forgot that we are talking about Boeing. They probably wanted to pass on the costs of changing the drawings and performing the necessary tests on to each of the operators for each aircraft at the full cost of the mod. That would be a substantial amount added to Boeings' bottom line.
It reminds me of a job that I did on a part made by a German company. What I did would normally be charged off to the customer at about $10,000. The German Company paid me well for my services but gave the analysis to Boeing for free. The subject part was the truck positioner for the 767 main landing gear. The contract was written in such a way that the German firm would supply 250 ship sets (500 parts)and,50% spares (250 units) with these parts being provided up front. The parts would then be paid for when each individual aircraft was sold or, when a spare was sold. My boss who was an American had a great deal of experience in product support, discovered that each unit was priced at $6400.00. He told the marketing department that the price should be twice that amount. They said that a profit of six percent was sufficient. My boss contacted a friend of his at Lufthansa who also was a Boeing tech rep. My boss asked what Boeing charged the airline for a spare truck positioner. He responded, $23,000
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The Cat
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
$110,000.00? You have to be kidding. How much does it cost to cut out a small section of hydraulic tubing and prepare the ends by flaring and then insert the fuse? Oh, I completely forgot that we are talking about Boeing. They probably wanted to pass on the costs of changing the drawings and performing the necessary tests on to each of the operators for each aircraft at the full cost of the mod. That would be a substantial amount added to Boeings' bottom line.
It reminds me of a job that I did on a part made by a German company. What I did would normally be charged off to the customer at about $10,000. The German Company paid me well for my services but gave the analysis to Boeing for free. The subject part was the truck positioner for the 767 main landing gear. The contract was written in such a way that the German firm would supply 250 ship sets (500 parts)and,50% spares (250 units) with these parts being provided up front. The parts would then be paid for when each individual aircraft was sold or, when a spare was sold. My boss who was an American had a great deal of experience in product support, discovered that each unit was priced at $6400.00. He told the marketing department that the price should be twice that amount. They said that a profit of six percent was sufficient. My boss contacted a friend of his at Lufthansa who also was a Boeing tech rep. My boss asked what Boeing charged the airline for a spare truck positioner. He responded, $23,000
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The Cat
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
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To use the alt flap, yes, but not as an alternate pitch control. My IP told me that the arrows on the panel were to warn of the direction of trim change, only because I would know what elevator to use to compensate. I only learned the real reason from another line pilot who had been trained in the US, a couple of years later. And the use of the flap as a pitch control is not covered in the manuals, so it probably does not have Boeing approval. I dunno! (and don't fly the Classic any more anyway)
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The use of flaps for pitch control was part of the alternate procedures in the CV880 QRH. Easy way to remember NUID (nude), nose up, inboards down. The B707 had the same capabilities but the procedure was not part of our alternate ops on that airplane.
[This message has been edited by HotDog (edited 08 January 2001).]
[This message has been edited by HotDog (edited 08 January 2001).]
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Total hydraulic failure is the one time I would rather not be flying a helicopter. Most of the larger types have NO manual reversion, with the flying controls effectively locked if all the systems fail.
You then remember the Microsoft motto: "Where DID you want to go today?"
You then remember the Microsoft motto: "Where DID you want to go today?"
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To: Shy Torque
Just the opposite. If you lose all hydraulics the controls don’t lock up. They are completely free to move due to the opening of the bypass valve inside the servo. When this happens you had better forget about having children as the cyclic will imediately start rotating in a circle driven by the feed back forces in the rotor system.
The Sikorsky S-55 could be flown without hydraulics but the lateral feedback forces were quite high and it made the cyclic difficult to handle. To compensate for this, they incorporated a servo that was powered by engine oil pressure but this servo was in a constant state of bypass as long as there was pressure on the hydraulic system. If the pressure dropped below a certain level (750 PSI I think) the primary servo bypass valves would open and the oil powered servo would come on line and power the two lateral servos which at this time are linkages in the control system.
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The Cat
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
Just the opposite. If you lose all hydraulics the controls don’t lock up. They are completely free to move due to the opening of the bypass valve inside the servo. When this happens you had better forget about having children as the cyclic will imediately start rotating in a circle driven by the feed back forces in the rotor system.
The Sikorsky S-55 could be flown without hydraulics but the lateral feedback forces were quite high and it made the cyclic difficult to handle. To compensate for this, they incorporated a servo that was powered by engine oil pressure but this servo was in a constant state of bypass as long as there was pressure on the hydraulic system. If the pressure dropped below a certain level (750 PSI I think) the primary servo bypass valves would open and the oil powered servo would come on line and power the two lateral servos which at this time are linkages in the control system.
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The Cat
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]