B737 Landing Gear Transfer Unit
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B737 Landing Gear Transfer Unit
I came across this comment from BOAC in an 18 month old thread.
This concerns the situation where you would have lost HYD Sytem A, consequently lowered the gear for landing and then having to divert. The general concensus is that the gear cannot be retracted without sys A. BOAC suggests that a 'wise old head' disagrees with this, I guess in order to reduce fuel burn and make it to a distant alternate.
To my surprise BOAC's posting was the final posting in this thread. Nobody bothered replying to this rather steep comment, strangly enough.
I guess you would shut down No1 and restart it as soon as the gear is up. You'll be in a lot of sh*t if it wouldn't restart off course. Is it worth the risk? I guess if you only had one alternate airport and can't make it with gear down it is worth thinking about.
Is it technically possible to use the LGTU in this manner? I think it is, correct me if I'm wrong.
Has anybody done this, for real or in the sim?
Why wouldn't Boeing design it that way? The system to retract the gear with Sys.B is there, but it will only operate with "Eng. No1 RPM below a limit value". How hard is it to make a switch to operate the LGTU at will?
There must be a good reason for that I would think.
Can anybody shed some light?
Ziggy
Originally Posted by BOAC
- it was suggested to me (years ago) by a 'wise old head' that shutting down No1 when conditions permit might allow the LGTU to raise the gear.
To my surprise BOAC's posting was the final posting in this thread. Nobody bothered replying to this rather steep comment, strangly enough.
I guess you would shut down No1 and restart it as soon as the gear is up. You'll be in a lot of sh*t if it wouldn't restart off course. Is it worth the risk? I guess if you only had one alternate airport and can't make it with gear down it is worth thinking about.
Is it technically possible to use the LGTU in this manner? I think it is, correct me if I'm wrong.
Has anybody done this, for real or in the sim?
Why wouldn't Boeing design it that way? The system to retract the gear with Sys.B is there, but it will only operate with "Eng. No1 RPM below a limit value". How hard is it to make a switch to operate the LGTU at will?
There must be a good reason for that I would think.
Can anybody shed some light?
Ziggy
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I've recently done my Boeing 737 type rating in Sweden. While there we had a number of insructors, mostly Scandinavian, some good, some appaling! However the point of the post is that we were told that a Nordic airline had just this problem. Lost Hyd Sys A, couldn't get into destination and alternate was a long old treck away. The crew, who knew their books well, decided to close down No 1, raise the gear, and then restart it. It all ended up with a happy ending and is a classic reminder that tech training these days is perhaps a little shallow. With the basic CBT training and never sight nor sound of a real instructor, how well do we know the aircraft systems? Not as well as we could?
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The crew, who knew their books well, decided to close down No 1, raise the gear, and then restart it. It all ended up with a happy ending and is a classic reminder that tech training these days is perhaps a little shallow.
Shut down one engine AND have the gear down would be a bit of a performance killer. On more occasions than I care to recall this sort of crew action results in a monumental cock-up and the a/c in a worse state than before.
Shut down one engine AND have the gear down would be a bit of a performance killer. On more occasions than I care to recall this sort of crew action results in a monumental cock-up and the a/c in a worse state than before.
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I have heard a heavy hint from a simulator trainer that if you were to fail the power supply to No.1 N1 gauge, you can fool the system into thinking No.1 has failed so the LGTU will then be powered and raise the gear.
I think the option to actually shut down and then relight is reasonable if you are up an alley with no other way out. It's not traumatic for the engine and has such a reliability of relighting that it's OK to do. If the only other alternative is to bust limits into a mountainous nasty place, I'd do it like a shot.
I think the option to actually shut down and then relight is reasonable if you are up an alley with no other way out. It's not traumatic for the engine and has such a reliability of relighting that it's OK to do. If the only other alternative is to bust limits into a mountainous nasty place, I'd do it like a shot.
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For the sake of completeness, here is that thread
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Originally Posted by Rainboe
I have heard a heavy hint from a simulator trainer that if you were to fail the power supply to No.1 N1 gauge, you can fool the system into thinking No.1 has failed so the LGTU will then be powered and raise the gear.
You should pop up the Battery bus circuit breaker right ?
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Anyone with a more technical background who can maybe shed some light on why Boeing doesn't offer this option or hasn't built the system with a switch to operate the LGTU?
I expect there to be a technical reason why you shouldn't do this, maybe the LGTU is not designed to deliver enough hydraulic capacity to take all three units up, but just has enough to assist the A system which is normally still working on the elec.hyd.pump.
Ziggy
I expect there to be a technical reason why you shouldn't do this, maybe the LGTU is not designed to deliver enough hydraulic capacity to take all three units up, but just has enough to assist the A system which is normally still working on the elec.hyd.pump.
Ziggy
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Nice one You should pop up the Battery bus circuit breaker right ?
On the 737NG you can fool the aircraft into thinking that engine #1 is shut down to operate the LGTU. We do this on airtests, at a safe altitude, to test the LGTU by pulling the ENG 1 RUN/PWR c/b (P18-2 B3 or thereabouts) and then retract the gear with the hyd A system off. There is no equivalent c/b on the classics and I would not recommend trying to find one, god knows what else you would inadvertently take out in the process.
Re the performance issue of one engine and the gear down; I can tell you from experience that even in a 20K 737-300 at about 44,000kg in the above config and flap 15, can just maintain level flight at 15,000ft – but it wont climb!
I have been given this no hyd A, gear down scenario in the sim myself and knew that by shutting down eng #1 (or pulling the c/b) I could get the gear up, but I have declined to do it due to the increased risk to the pax. Now that you have the knowledge it is between you, your training dept & your conscience to decide what to do given your particular circumstances.
S&L
Re the performance issue of one engine and the gear down; I can tell you from experience that even in a 20K 737-300 at about 44,000kg in the above config and flap 15, can just maintain level flight at 15,000ft – but it wont climb!
I have been given this no hyd A, gear down scenario in the sim myself and knew that by shutting down eng #1 (or pulling the c/b) I could get the gear up, but I have declined to do it due to the increased risk to the pax. Now that you have the knowledge it is between you, your training dept & your conscience to decide what to do given your particular circumstances.
S&L
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"....and knew that by shutting down eng #1 (or pulling the c/b) I could get the gear up, but I have declined to do it due to the increased risk to the pax."
The increased risk is obvious in the shutdown case. I'm not familiar with what the cb does, so please tell me, is there risk in pulling it?
I'm sure I'll never even get close to needing a last resort solution like this as long as I only fly within Europe but just out of curiosity I'll go and try it in the sim next month if time permits.
Ziggy
The increased risk is obvious in the shutdown case. I'm not familiar with what the cb does, so please tell me, is there risk in pulling it?
I'm sure I'll never even get close to needing a last resort solution like this as long as I only fly within Europe but just out of curiosity I'll go and try it in the sim next month if time permits.
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Batt bus powers amongst other things the Fire Det, Gear lever Latch,
Pack valves, Sby horizon, Eng start valves and sby rudder valves. From a technical point of view this is all very interesting. However, personally, I think that anyone thinking of attempting these exercises needs their head examining!
Pack valves, Sby horizon, Eng start valves and sby rudder valves. From a technical point of view this is all very interesting. However, personally, I think that anyone thinking of attempting these exercises needs their head examining!
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ziggy:
the system was designed to work automatically in the most critical situation possible: engine failure after V1, or during go-around.
In such a case it's criticall to raise the gear asap,so if LGTU senses low eng1 RPM ,thus low output from eng1 hyd pump (even if sysA elec pump it's still working ---it's not a loss of hyd sys A ) then sysB supplies the hyd volume necessary to raise the gear at a normal rate.
Now,you may say what if you have a loss of sysA during take-off.You'll still have 2 engines running,a less critical situation during t-off,giving you plenty of time to asses your situation after climbing to a safe altitude.
You can contact maintainance,find out what CB to pull,or decide to shutdwn eng1,whatever.It's almost no risk in shutting down and restarting an engine,if it's done properly.
Brgds Alex
the system was designed to work automatically in the most critical situation possible: engine failure after V1, or during go-around.
In such a case it's criticall to raise the gear asap,so if LGTU senses low eng1 RPM ,thus low output from eng1 hyd pump (even if sysA elec pump it's still working ---it's not a loss of hyd sys A ) then sysB supplies the hyd volume necessary to raise the gear at a normal rate.
Now,you may say what if you have a loss of sysA during take-off.You'll still have 2 engines running,a less critical situation during t-off,giving you plenty of time to asses your situation after climbing to a safe altitude.
You can contact maintainance,find out what CB to pull,or decide to shutdwn eng1,whatever.It's almost no risk in shutting down and restarting an engine,if it's done properly.
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The clue to solving this is in the MEL. If you fly an NG you will notice that N2 guages are not mentioned-so they are both required for dispatch. The old base check curly one was to fail the eng. one N2 guage on taxi out (after dispatch and now into the QRH)-the survivors of this were the ones who called engineering BEFORE takeoff-the others well......
On the basis that AC lies and DC dies the pulling of the CB MUST be an option before shutting down an engine. Also remember that the manual gear extension door in the flight deck is monitored if the contact is "open" the gear will not retract-a good stamp on it during the "rainbow" check will buy some insurance.
On the basis that AC lies and DC dies the pulling of the CB MUST be an option before shutting down an engine. Also remember that the manual gear extension door in the flight deck is monitored if the contact is "open" the gear will not retract-a good stamp on it during the "rainbow" check will buy some insurance.
Transparency International
I think the LGTU trigger is N2 below a certain value which is just below flight idle....
I've have seen it demonstrated in a sim and recall that as soon as LGTU was activated one could add fuel again and the engine would be up and running before gear retraction was completed.( -3-4-500)
I've have seen it demonstrated in a sim and recall that as soon as LGTU was activated one could add fuel again and the engine would be up and running before gear retraction was completed.( -3-4-500)
50% N2 (NG) / 56% N2 (Classics).
Just my twopenneth, but unless you are familiar with shutting down & relighting engines I would do it in a slow and deliberate way from the checklists. QRH - Engine failure & shutdown followed by In-flight start checklists. Especially as you have another non-normal config to deal with.
It may sound slick to cut the fuel off, allow the engine to decay to the point where the LGTU kicks in, retract the gear and put the fuel back in; but the aircraft will be quite a handful during all of this. Do it slowly, methodically and safely.
I stick by my original post that there would have to be no alternative before I got to the stage of shutting down a good engine with pax on board.
S&L
Just my twopenneth, but unless you are familiar with shutting down & relighting engines I would do it in a slow and deliberate way from the checklists. QRH - Engine failure & shutdown followed by In-flight start checklists. Especially as you have another non-normal config to deal with.
It may sound slick to cut the fuel off, allow the engine to decay to the point where the LGTU kicks in, retract the gear and put the fuel back in; but the aircraft will be quite a handful during all of this. Do it slowly, methodically and safely.
I stick by my original post that there would have to be no alternative before I got to the stage of shutting down a good engine with pax on board.
S&L
Transparency International
Didn't mean to hurry anything/one - just to say that once the LGTU has been activated it will stay activated even if the engine is relighted.
Pulling CBs may not produce the desired result but could enduce some undesired results.
Anyway, the whole subject is extra-curricular. Why don't Boeing offer an expanded checklist for this item?
Pulling CBs may not produce the desired result but could enduce some undesired results.
Anyway, the whole subject is extra-curricular. Why don't Boeing offer an expanded checklist for this item?
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D to D,
May be its a legal thing. A bit like you can have a single engine failure but only loss of thrust on both engines.
To admit that your product is fallible might invite product liability etc. The LGTU is in place to retract the gear in a SE case enabling the a/c to meet and exceed the min climb gradient for certification for individual and fleet wide aircraft. A bit like the remote vs unlikely case-they both have a % odds probability which we as pilots and passangers have accepted as safe-which it is.
May be its a legal thing. A bit like you can have a single engine failure but only loss of thrust on both engines.
To admit that your product is fallible might invite product liability etc. The LGTU is in place to retract the gear in a SE case enabling the a/c to meet and exceed the min climb gradient for certification for individual and fleet wide aircraft. A bit like the remote vs unlikely case-they both have a % odds probability which we as pilots and passangers have accepted as safe-which it is.
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D2D........nope it will auto reset (the "dolls eye indicator will let engineering know it has happened / been tinkered with when it lands.) Raising the gear with "B" and lowering with "A" leads to a mess when retracts are carried out on Jacks and a loss of Hydralic fluid in other cases (Boeing states 1/2 a gallon per retract..!!!!)
Fruitloop,
Is there any transfer of hydraulic fluid from one system to the other during LGTU operation?
Where is the hydraulic fluid lost from? I dont see any evidence of this after a flight where I have used the LGTU, but I suppose it could have blown away by the time of landing.
S&L
Is there any transfer of hydraulic fluid from one system to the other during LGTU operation?
Where is the hydraulic fluid lost from? I dont see any evidence of this after a flight where I have used the LGTU, but I suppose it could have blown away by the time of landing.
S&L
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Originally Posted by screwdriver
Batt bus powers amongst other things the Fire Det, Gear lever Latch,
Pack valves, Sby horizon, Eng start valves and sby rudder valves. From a technical point of view this is all very interesting. However, personally, I think that anyone thinking of attempting these exercises needs their head examining!
Pack valves, Sby horizon, Eng start valves and sby rudder valves. From a technical point of view this is all very interesting. However, personally, I think that anyone thinking of attempting these exercises needs their head examining!
no one is going to pull the battery bus CB obviously in this life or in another one... it is just for the sake of some brainstorming.