complete hydraulic failure

[purple haze]

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.

[Mark 1]

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.

[CargoRat2]

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

[RATBOY]

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.

[dc8ray]

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

[spanners]

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

[Tor]

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.

[Lu Zuckerman]

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).]

[Prof2MDA]

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...

[static]

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.

[purple haze]

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).]

[askcv]

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.

[CargoRat2]

Spanners; Thanks for that. I thought the hydraulic lines had been re-routed.

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rgds Rat

[BEagle]

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.

[Lu Zuckerman]

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).]

[AhhhVC813]

askcv
In the uk it is an implicit part of conversion and recurrent training that 747 classic pilots know how to use the alt flap extension. By your comments is it thus safe to assume it's not in other places???????????

[askcv]

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)

[HotDog]

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).]

[ShyTorque]

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?"

[Lu Zuckerman]

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).]

[ShyTorque]

Lu,

You are certainly correct for some helicopters, possibly all Sikorsky ones. I flew the Whirlwind in full manual once and can confirm what you say about the feedback forces.

However, I believe some Aerospatiale designs are as I describe, depending on the configuration of the main servos and flying controls.

We are splitting hairs here as the outcome would be the same.

[This message has been edited by ShyTorque (edited 09 January 2001).]

[Lu Zuckerman]

To: Shy Torque

If what you say is true, then you would not be able to move the flight controls while on the ground unless the hydraulics were powered. On the newer Aerospatial helicopters as well as other helicopters that use elastomeric bearings moving the unpowered controls is difficult. But not incorporating bypass valves in the servos is like condemning the pilot and passengers to death if hydraulics fail. I don’t think the helicopters could be certified if that were true. Perchance your opinions stem from trying to move the controls with no hydraulics. What you interpret as the system being locked is the resistance of the elastomeric bearings.

I don't know for sure but it would seem that helicopters with elastomeric bearings should have dual hydraulics because of the stiffness problems. A helicopter with these bearings and with a single hydraulic system woud be extremely difficult if not impossible to control in the event of a total hydraulic failure.


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The Cat

[This message has been edited by Lu Zuckerman (edited 09 January 2001).]

[ShyTorque]

Lu,

Yes, I have flown an aircraft where the controls could not be moved until the rotor rpm increased enough to power up the hydraulics. The military AS-330J is like this; it has a fully articulated head and no elastomerics.

This aircraft was originally designed and supplied with a disconnect in the No. 1 engine input, to allow the engine to run the No. 1 hydraulic system and No. 1 AC generator for ground servicing (these were / are primarily AC aircraft with the generators running off the main gearbox accessories). However, the "disconnect" facility was modded out of our fleet as they could slip in flight. I seem to remember if this happened the No.1 hydraulics and the No. 1 AC generator would go off line, but more importantly, the (only) MGB oil pump would stop as well, which took the shine off your day.

On these aircraft, if a single hydraulic failure occurred, the aircraft would be put down asap for obvious reasons. I spent a few occasions in fields waiting for hydraulic repairs during my time operating them.

However, it is academic only whether the cyclic becomes rigid or thrashes round the cockpit following a complete hydraulic failure. You cannot control the aircraft in either case. A joke we used to make was that in the unfortunate event of a total hydraulic failure the pilot's immediate actions would be to unstrap, drop trousers, sit on the cyclic. Just to give the BOI something to think about!

Another nasty problem with these aircraft was that if one of the two separate tail rotor servo control "pull" cables snapped, the servo would run to full travel the opposite way. This would result in either full positive or full negative T/R pitch, which rendered the aircraft uncontrollable in yaw. I know for sure that the RAF fleet flew like this for over twenty years but I understand they now have been modded with a centering device for the servo valve which gives some level of control, like later Sikorsky designs.

And then there was the engine response (Turmo 3C4) which was appalling from flight idle, due to the lack of a collective anticipator in the FCU design...

You are correct about the lack of certification for civilian use. There were many mods and additions to the civil version.

Edit: If we are going to continue discussing this we perhaps ought to start a new thread on Rotorheads as I feel we have diverted from Purplehaze's original line of discussion. Sorry, PH! :)

[This message has been edited by ShyTorque (edited 09 January 2001).]

[before landing check list]

Speaking from limited experience(compared to some of you here) the UH1H flew just fine with out hydraulics. You just had to learn to relax a bit and not to turn on the hydraulics back (close to the ground)or in the case of a actual failure, turn them off as a precaution against getting them restored close to the ground without input from the pilot. The UH1 has one system. The civilian varient the B205 has 2 systems. The UH1N and BH212/412 both has 2 systems but would fly fime without any, with practice of course. The MD500/530 did fine without hydraulics. The BO105 had a rigid rotor so you needed one to fly ALL THE TIME but it had two, very reliable and safe.The AS350 uses a starflex rotor head(composite) and accumulators incase of hydraulic failure. The UH60 Blackhawk had 3 systems. Two mains driven off of the transmission and one electric(all 3 identical pumps) Would fly just fine with just one. But you had to have one, or else. You could fly with the pilot assist(boost off but you needed to practice, like all things.
hope this helps
j

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Here's to cheating, stealing, fighting, and drinking.
If you cheat, may you cheat death.
If you steal, may you steal a woman's heart.
If you fight, may you fight for a brother.
And if you drink, may you drink with me.

[This message has been edited by before landing check list (edited 10 January 2001).]