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Hydraulic system loading
A few times I've seen quips about avoiding using multiple hydraulic systems (like gear and flap movement) simultaneously, because of the extra wear and tear the increased load can put on the system. But this doesn't make sense to me, and I'd like to make sense of it, or confirm that it's bunk. With other types of systems I can see the issue. With electrical, we have increased current and heat flowing through the components. With mechanical systems, we get closer to the yield limits, increased chance of fatigue cracks, etc. With an engine, the implications of loading it more are obvious.
But with hydraulics, we have have fluid, pushed by a pump, staying at a regulated pressure, and running through actuators. With multiple systems using it simultaneously, of course it takes more flow to get the job done (and maybe the pressure would decrease), but there's no more pressure or stress on the lines or actuators. As for the pumps, if anything I see this easing their load as they're pumping against less resistance. Maybe I'm looking at this simplistically, but what am I missing? |
For certain abnormals, you'll notice the decreased system response time. I move gear, flaps, and primary flight controls simultaneously on the A320. Never had a problem. We have some pretty esoteric limitations in our books. If hydraulic loading posed a practical (as opposed to theoretical) problem, I'm sure it'd be in the book.
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I think it has to do with the caudal of hydraulic liquid available in the system. You can have same pressure, but with lesser quantity some systems (heavy users), might not work completely fine.
I was a fan of switching in the yellow electric hydraulic pump when on the APU during an emergency landin with both engines flame out (only in the sim!), until one day the checker asked an obvious question: - "Why you doing that Iggy?" - "For the benefit of having the yellow hyd system working in a situation when control of the airplane and braking power is needed the most?" - "Don't you think that, if doing that was somehow helpful, they would have written down it on the list?" - "But, they are French, and we know better than them in this airline, right?" - ... - "Right?" - "Look, if it is an obvious thing to do, but it is not written, there must be a reason for it. And in this case, the reason is that the caudal (the amount of liquid, I'm not sure if you know the word caudal, Iggy), that the electric pump can deliver is around four times less than the caudal delivered by the EDP. Understood?" - "Yes Sir!" - "Ok, now do me 50 push ups, you are fat". So, not being in the book means has more to do with people like me being allowed in the cockpit more than being esoteric. |
Originally Posted by iggy
(Post 11160752)
I was a fan of switching in the yellow electric hydraulic pump when on the APU during an emergency landin with both engines flame out (only in the sim!)
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Watch the system pressure when operating multiple systems. Especially landing gear. There may be your answer.
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Sometimes it’s a case of mechanical sympathy versus ‘approved operations’.
Best action vs ‘technically not a limitation’. Although whatever you do to enhance the lifespan is negated by the knucklehead before you and the one after you. If the name on the paycheck is the one that’s on the tail then you follow whatever their procedures are. |
Originally Posted by iggy
(Post 11160752)
the reason is that the caudal (the amount of liquid, I'm not sure if you know the word caudal, Iggy)
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Originally Posted by DaveReidUK
(Post 11160784)
I'm not sure if any of the rest of us do, either - have you just made it up ? :O
What would the correct term be in this context? Thanks! |
Pump specifications
https://tinyurl.com/2p967x24
I would assume the ability to operate multiple systems simultaneously will be limited by the maximum output flow (discharge). |
Originally Posted by iggy
(Post 11160788)
:ugh::ugh::ugh::ugh: That's the Spanish for discharge, which I don't know if also can apply to the topic. I guess the checker was right telling me to do push ups and zip it :O:O
What would the correct term be in this context? Thanks! |
Swash plate pump? higher demand higher angle of plate, more friction on slipper pads, case drain filter blockage, more flow generates more heat; excessive high system demand can lead to knock / vibration; jerky operation of hydraulic motors can exacerbate drive shaft wear and cause system lock out ( mainly flaps). Could cause priority valves, where fitted, to hammer leading to such items as extending gear extension time, longer unclean door configuration flight mode.
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Originally Posted by vilas
(Post 11160815)
Fluid turn over. To your yellow pump use in double flame out you were not far wrong. I asked this question Airbus replied to me saying when in dual flame out case when eventually G+Y pressure drops low ECAM will ask for Yellow electric pump with PTU OFF because the fluid turn over is less for powering two systems. Then they replied to another by saying the flap may lower erratically and may not lower to desired position but for yellow brakes surely that will help.
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Originally Posted by iggy
(Post 11160912)
Thanks Vilas!!!
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I think aeromech3 mentions good reasons for operating one hydraulic service at a time.
Other reasons might be : Hydraulic pressure might drop so the services might not reach the intended positions correctly. This might produce a warning or it might not, but it could cause a lock-out - for example of flap or slat WTBs - leading to problems you would prefer not to have. If, say the gear and flaps were operated together and the aircraft suddenly banked over un-commanded; which service caused the problem, and therefore which will remove the problem ? Best to operate one service at a time if you can and confirm the correct operation, travel and lock of each position before operating the next. (Apart from normal ailerons, elevators and rudder, obviously, which are designed to be operated together). |
Then how come Boeing say “Gear down, Flap xx” simultaneously on a bunch of their fleet?
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Originally Posted by Check Airman
(Post 11160741)
For certain abnormals, you'll notice the decreased system response time. I move gear, flaps, and primary flight controls simultaneously on the A320. Never had a problem. We have some pretty esoteric limitations in our books. If hydraulic loading posed a practical (as opposed to theoretical) problem, I'm sure it'd be in the book.
WHEN FLAPS ARE AT 2...........L/G DOWN ORDERL/G lever .....................................SELECT DOWN AUTO BRK....................................CONFIRM If the runway conditions have changed from the approach briefing, consider another braking mode. GROUND SPOILERS ARMEXTERIOR LIGHTSNOSE sw T.ORWY TURN OFF sw ON WHEN LANDING GEAR IS DOWN FLAPS 3 ...........................................ORDER FLAPS 3 ............................................SELECT ECAM WHEEL SD page ...........CHECK WHEEL SD page appears below 15 500 ft when landing gear is extended. Check for three green indications on the landing gear indicator panel. At least one green triangle on each landing gear strut on the WHEEL SD page is sufficient to indicate that the landing gear is downlocked. Rely also on the “LDG GEAR DN” green LDG MEMO message to confirm that the landing gear is downlocked. If residual pressure is indicated on the triple indicator:RESIDUAL BRAKING PROC APPLYDue to the accomplishment of the alternate braking functional test after the landing gear is downlocked, brief brake pressure indications may be observed on BRAKES PRESS. FLAPS FULL .............................ORDER FLAPS FULL ..............................SELECT |
I don’t read that as “wait for three greens to move the flaps”.
I still believe that if a problem existed, it would be specifically prohibited. At both companies I’ve flown the plane, we call for gear and F3 simultaneously, and more often than not, Flap full before we have 3 greens. Haven’t heard of anyone having a problem so far. |
I think if you read the Airbus SOPs like that then you would not be able to lower the gear for drag if you were hot and high. Because what you’re saying vilas, is that you can only select F3 once the gear is fully down and you can only select gear down once F2 is fully set. So how can you put the gear down if you haven’t got F2 set?
If you say you can select gear down without F2 being fully set then the argument that that’s what the book says is invalid. It’s semantics to a point but I don’t read the SOPs like that. What do you think? |
Originally Posted by BoeingDriver99
(Post 11164275)
I think if you read the Airbus SOPs like that then you would not be able to lower the gear for drag if you were hot and high. Because what you’re saying vilas, is that you can only select F3 once the gear is fully down and you can only select gear down once F2 is fully set. So how can you put the gear down if you haven’t got F2 set?
If you say you can select gear down without F2 being fully set then the argument that that’s what the book says is invalid. It’s semantics to a point but I don’t read the SOPs like that. What do you think? Check Airman Nothing has happened philosophy is not used to deviate from the book. There many things one can do differently and normally nothing happens and yet something can happen.The book specifically tells you to take Flap3 when gear down. If it had no meaning then there was no need to mention WHEN GEAR DOWN select Flap3. In Airbus we lower flaps through SFCC and gear through LGCIU. So we make a selection we confirm flap number or call gear down by three Reds for gear to confirm the computer is working but when it says when Flap2 or when gear down then the surface has to be checked at the correct position or three greens for gear. Gear is a high demand system so a pause is indicated. Besides when gear is selected down you need to check AB selection, if required then change it , spoilers need to be armed turn off taxi lights to be put in. If there's a short cut something will be missed. |
And I think you are reading the placement of a sentence in a sequence of SOP as a “must be done this way” approach.
Another example would be the flight control check - in the FCTM Airbus state up/down, left/right, rudder - left/right. Would you be wrong to check the flight controls right/left or down/up? Or does Airbus have to write the sequence a certain way and the sequence is not important - it’s just written down that way and nothing prohibits you from checking down/up, right/left. Everyone does it the way it’s written but would it make any difference whatsoever to do it another way? What if Airbus decided to write it the other way? Would the old way be “wrong” and the new way “right”? If it was a problem and had associated threats then Airbus could put in a Limitation, or a Note, or in the FCTM Preventing Identified Risks section but they don’t. Perfectly happy to to be happy to disagree with you. Has anyone ever experienced an issue selecting gear and flaps at the same time? Any first hand evidence? Ps. The gear takes 15-21 seconds to extend - AMM 32-31-00-720-002A. I’m pretty sure most pilots can check the AB, arm the spoilers, turn on two lights inside 15 seconds. And if necessary select F3. |
Even in B747 classic we ordered gear down and Flap3 together but with a rider " gear down when three greens flaps 3
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I think you may be taking an overly prescriptive view of what’s written in the SOP. Our manual says to turn the speaker on to do the oxygen check. It doesn’t say to turn it back off. I don’t take that to mean we have to fly with the speaker on.
I agree that “nothing’s happened yet” is by itself not necessarily a solid argument, but coupled with the facts that Airbus hasn’t listed a specific limitation against it, I think it’s fine. I’m willing to reverse my stance if there’s any technical word from Airbus against doing so though. |
https://cimg4.ibsrv.net/gimg/pprune....16d16f0273.png
Airbus training power point |
Isn't it also good airmanship to only change 1 configuration at a time?
Flap 2 - balloon - trust back - trim forward Gear down - more drag - trust up - trim back |
Originally Posted by cav-not-ok
(Post 11164586)
Isn't it also good airmanship to only change 1 configuration at a time?
Flap 2 - balloon - trust back - trim forward Gear down - more drag - trust up - trim back Then, if pitch/drag effects of simultaneous config changes are known ahead of time, they can be counteracted simultaneously ahead of time, too. |
Originally Posted by vilas
(Post 11164523)
https://cimg4.ibsrv.net/gimg/pprune....16d16f0273.png
Airbus training power point You point to the fact that it says "when gear is down". There's an argument to be made for that logic, but I'll reiterate, if there was an actual danger in moving the gear and flaps simultaneously, they'd have put that in the limitations chapter. They found time to include a maximum speed in a turn above 76T. The navigation section of the limitations chapter if full of both esoteric, and general limitations. I find it difficult to believe that moving the gear and flaps simultaneously cases undue stress, and they didn't include it in the limitations section. Worth noting that for GA, it doesn't say to wait for the flaps to lock before raising the gear. Surely raising the ear puts more stress on the system than lowering it. |
The point I am making is Airbus says so and teaches it so. You can't say they don't. On the other hand no where is it written that gear and flaps can be taken at the same time. There are a few thing which may not be limitations but good practices. Ask Airbus on techrequest if you want to do differently. Settings heading ang pulling or pulling first and setting the heading. People find no difference and yet Airblue captain in circling approach under pressure of marginal weather kept dialling and then pulled and aircraft turned shorter way into the hill 160 people lost their lives. Making procedures in FBW is not line pilot's job.
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Vilas, any chance you can ask Airbus about it?
I personally always wait for the gears and doors to be locked before asking next notch of flaps unless I find myself in a situation where I screwed up and configured too late. Otherwise, there is no rush to set flaps while gears are still in transit. |
Good practice to do one major thing at a time, so that pilots can confirm correct selection, correct movement and correct final position. If you get an uncommanded roll after dropping gear and flap together. which service is causing the uncommanded roll?
No need to rush in aviation if you are doing it right. So why put your hydraulic system to maximum load if you don't need to? A good pilot will respect their aircraft mechanisms. In a go-around, as you know, the call is "Go around, flap" <select flap> then read out FMA. Then PM will call "positive climb", then PF will call "gear up", <select gear-up> , so the two things are not simultaneous and by the time the gear is called for the flaps will have finished moving. |
Originally Posted by pineteam
(Post 11164856)
Vilas, any chance you can ask Airbus about it?
I personally always wait for the gears and doors to be locked before asking next notch of flaps unless I find myself in a situation where I screwed up and configured too late. Otherwise, there is no rush to set flaps while gears are still in transit. |
Originally Posted by aeromech3
(Post 11160905)
Swash plate pump? higher demand higher angle of plate, more friction on slipper pads, case drain filter blockage, more flow generates more heat; excessive high system demand can lead to knock / vibration; jerky operation of hydraulic motors can exacerbate drive shaft wear and cause system lock out ( mainly flaps). Could cause priority valves, where fitted, to hammer leading to such items as extending gear extension time, longer unclean door configuration flight mode.
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Quote :
WHEN LANDING GEAR IS DOWN FLAPS 3 ...........................................ORDER FLAPS 3 ............................................SELECT Check Airman : I don’t read that as “wait for three greens to move the flaps”. Are you sure ? "WHEN" seems fairly clearly to be a conditional clearance, relying on something else having finished first, in this case the landing gear being down. i.e. you wait until the landing gear is down before moving the flaps further. How do you know the landing gear is down? = you have three/four green lights on the Gear panel and/or at least three/four green triangles on the Wheels page. |
I typed up a much longer response, but it got lost in the ether of the internet.:ugh:
I'll skip to the good part. If Airbus can answer the question of whether there are any short or long term negative effects of moving flaps and gear simultaneously, I'll be happy to change the way I do things. |
Originally Posted by Uplinker
(Post 11165136)
Quote :
WHEN LANDING GEAR IS DOWN FLAPS 3 ...........................................ORDER FLAPS 3 ............................................SELECT Check Airman : I don’t read that as “wait for three greens to move the flaps”. Are you sure ? "WHEN" seems fairly clearly to be a conditional clearance, relying on something else having finished first, in this case the landing gear being down. i.e. you wait until the landing gear is down before moving the flaps further. How do you know the landing gear is down? = you have three/four green lights on the Gear panel and/or at least three/four green triangles on the Wheels page. Configuration Management chapter is quite specified , WHEN sounds quite conditional. And it seems very strange that you read it in another way. So you want them to write it in a way : "Please wait until gears are dn"? So tonight I'll make techrequest about it;) |
We sent a Tech Request a while ago and this is what Airbus said about this topic (320 family; there are other reasons to select gear down as per SOP on, say the 350, e.g., for the PLT to finish before landing):
The SOP philosophy regarding landing gear extension is to get it down and locked before reaching the final landing configuration. As either CONF FULL or CONF3 may be used for the landing, the SOP therefore requires selecting the landing gear down before selecting FLAPS 3, in order that landing gear extension is independent from the final selected landing configuration. This SOP recommendation was established to cope with the fact that the "L/G: GEAR NOT DOWN" red warning is triggered if the aircraft comes down to 750 ft radio height, with landing gear lever not in the down position. Indeed, if this SOP recommendation is not followed, i.e. if, for example, the landing gear and flaps 3 are selected simultaneously, and if the flaps/slats extension sequence is started a bit late, the landing gear selection may be close to this altitude threshold. Another point is that the L/G: GEAR NOT DOWNLOCKED warning is triggered if the landing gear extension sequence is not completed after 30 seconds: thus, selecting the L/G down after flaps 2 extension allow a comfortable reaction time, in the event that the warning is triggered. Finally, for each SLATS/FLAPS setting, the autotrim function trim the aircraft. The same applies when the landing gear is set to down. Waiting the landing gear is down locked before selecting Conf 3 allows getting the aircraft trimmed before a new SLATS/FLAPS configuration. For all these reasons, we recommend to select the landing gear down before selecting FLAPS 3. However, there is no technical objection for selecting CONF 3 or CONF FULL before L/G extension sequence as long as the maximum speeds to operate SLATS/FLAPS and L/G are respected. |
Sideline gripe on linguistics and not hydraulics. I read this sentence: "The SOP philosophy regarding landing gear extension is to get it down and locked before reaching the final landing configuration." and thought WTF kind of sentence is this, the gear is down before you're in landing configuration by definition, there's no logically possible way to have this problem to need avoiding. Gear up in landing configuration is an oxymoron.
Well, the context of the rest of the paragraph sheds light on that "configuration" here means flaps. OK, but we already have a word for that: "flaps!" Now, we're sacrificed a perfectly useful word (configuration) at the altar of long and impressive technical words for ornamentation... we can be in "final landing configuration" but land gear up :rolleyes: (Oh, maybe they wanted that to specify flaps AND slats, not to be confused with flaps only? To avoid the mass confusion and chaos of every other airplane that just calls it "flaps" and everyone understands that it includes both? How about, oh, "flaps/slats" which still leaves "configuration" to mean that you can be configured for landing and have a normal safe landing?!) |
Originally Posted by Vessbot
(Post 11166221)
Sideline gripe on linguistics and not hydraulics. I read this sentence: "The SOP philosophy regarding landing gear extension is to get it down and locked before reaching the final landing configuration." and thought WTF kind of sentence is this, the gear is down before you're in landing configuration by definition, there's no logically possible way to have this problem to need avoiding. Gear up in landing configuration is an oxymoron.
Well, the context of the rest of the paragraph sheds light on that "configuration" here means flaps. OK, but we already have a word for that: "flaps!" Now, we're sacrificed a perfectly useful word (configuration) at the altar of long and impressive technical words for ornamentation... we can be in "final landing configuration" but land gear up :rolleyes: (Oh, maybe they wanted that to specify flaps AND slats, not to be confused with flaps only? To avoid the mass confusion and chaos of every other airplane that just calls it "flaps" and everyone understands that it includes both? How about, oh, "flaps/slats" which still leaves "configuration" to mean that you can be configured for landing and have a normal safe landing?!) But I take your point |
Originally Posted by CrazyStuntPilot
(Post 11166200)
We sent a Tech Request a while ago and this is what Airbus said about this topic (320 family; there are other reasons to select gear down as per SOP on, say the 350, e.g., for the PLT to finish before landing):
1. The response concludes with them saying there's no technical objection. I take that to mean the hydraulics aren't an issue. 2. I'm not aware of any US airline that will allow you to continue a landing if you're not fully configured by 1000ft, so the 750ft point is moot That said, you(pl) were right, and it seems Airbus wants it to be a 2 step process. I'll do my best to remember that on my next trip. My learning continues. |
Originally Posted by Check Airman
(Post 11166233)
2. I'm not aware of any US airline that will allow you to continue a landing if you're not fully configured by 1000ft, so the 750ft point is moot
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Originally Posted by pineteam
(Post 11166241)
Even for visual approaches??
(and no, you can't cheat and reconfigure for a flaps 3 instead of full at 980ft) What altitude do you use for visuals? |
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