Airbus direct law landing
Technique for direct law landings.
If you're in alternate law, lowering the gear puts you in direct law and auto trim is lost. So I think the technique is to fly the approach stabilised, landing flap, @Vapp (to get it all trimmed out nicely) and THEN lower the gear and no further trim changes should be necessary. Is that the general technique? I notice the QRH for G+Y hydraulic specifically requests this for example, but struggling to find other examples. |
It’s not really necessary for a non hydraulic induced direct law landing as manual pitch trim is available via the trim wheels. Why the G+Y hyd QRH says to do that is due to the fact the THS is also lost, so when the landing gear goes down the elevators are set in a “null” position so the aircraft is “trimmed” to a stick neutral position.
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Originally Posted by Jonty
(Post 11186654)
It’s not really necessary for a non hydraulic induced direct law landing as manual pitch trim is available via the trim wheels. Why the G+Y hyd QRH says to do that is due to the fact the THS is also lost, so when the landing gear goes down the elevators are set in a “null” position so the aircraft is “trimmed” to a stick neutral position.
What has confused me is that the STAB JAM QRH just says "If MAN PITCH TRIM not available: For landing: use flap 3" Wheras the FCOM then also includes the instruction "When Conf 3 and VAPP: L/G DN" Any idea why the QRH doesn't include this info? Thanks for your help. |
Jam stab if ELAC doesn't detect it then there will be no ECAM actions and aircraft will remain in normal law. In that case QRH procedure will be applied. The manual trim remains available and if not then elevator holds it's position, so it's not necessary to lower gear at Vapp. But when ELAC detects Jam stab aircraft will go in Alternate law and appear on ECAM. If stab trim is not available the ECAM will ask gear to be lowered at Vapp.
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I think the thing to remember is that this scenario (gear down at Vapp) is linked to the condition of the stabiliser, and not wether you’re in direct law or not.
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Yes, I see now. Thanks for your help, those answers are great! Cheers.
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Just a comment. In direct law, the pitch direct law is a direct stick-to-elevator relationship(elevator deflection is proportional to stick deflection) and so is the FLARE MODE in normal law. FLARE MODE is also a direct stick-to-elevator relationship( with some damping provided by the load factor and the pitch rate feedbacks) as well as the memorization of the aircraft's attitude at 50ft.
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Actually in normal and alternate law a software called integrater moves and holds the elevator to commanded position till stab trim catches up. In direct law integrater is not available. So, when stab is jammed due hydraulic or any reason it helps to get the speed to Vapp so the elevator is positioned at Vapp with stick in neutral and then put gear down. If the gear was lowered at higher speed then at Vapp in approach the nose will drop and to maintain the approach path stick will require to be held aft of neutral. This compromises side stick aft range. And in case of go around it may not be possible to raise the pitch to 15°.
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Originally Posted by vilas
(Post 11187417)
Actually in normal and alternate law a software called integrater moves and holds the elevator to commanded position till stab trim catches up. In direct law integrater is not available. So, when stab is jammed due hydraulic or any reason it helps to get the speed to Vapp so the elevator is positioned at Vapp with stick in neutral and then put gear down. If the gear was lowered at higher speed then at Vapp in approach the nose will drop and to maintain the approach path stick will require to be held aft of neutral. This compromises side stick aft range. And in case of go around it may not be possible to raise the pitch to 15°.
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Originally Posted by CMpilot1
(Post 11188195)
The above explanation holds good for a DUAL HYD G+Y failure. However, in other cases where the airplane switches to direct law after selecting the gear down--e g. "DUAL RA FAULT", I don't think it is necessary to wait for the Vapp and selection of flaps 3 to lower the gear. In this case since the MAN PITCH TRIM is available, you could configure the airplane as you normally would.
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Originally Posted by vilas
(Post 11188510)
That's true. As I said if stab is jammed only then. However many instructors teach to lower the gear after flap3 even in case of Dual RA. According to me this doesn't serve any purpose except postponing direct law by may be 15 seconds. Since you are going to fly in direct law till touchdown these 15secs should not be such a problem. According to me there are only two cases for non-standard configuration i.e. G+Y 1,2,3 and gear down and G+B gear down 1,2,3.
In my previous airline I was taught to do it like this no matter the fault. Then recently on an OPC in new outfit, without thinking much of it during an unreliable speed approach I called for non standard F3 before LG down (despite the procedure indeed calling for normal F2 then manual gear extension and then F3), until I was stopped by the instructor, telling me it is dangerous to go away from the procedure. I mean at the end of the day it doesn't change much and certainly doesn't jeopardize the safety of the flight to do it one way or another. Just showed me once more how formatted we can get! EDIT : Now that you mention it, I had forgotten about G+B special config also. Well makes my point somewhat weaker indeed! Procedures are here for a reason. Makes me question my former outfit now though |
In the sprit of standardization, wouldn't it be easier to always do the same for direct law with gear down after flaps 3 and Vapp? |
Originally Posted by Scagrams
(Post 11188553)
Makes me question my former outfit now though
A few years ago we introduced a "new" function within the FDM of my operator, that is the capability to detect non standard configuration changes, i.e. anytime F3 was selected with LG still up and it would trigger (and still does) a Level 2 alert (nothing much just an email where you are told to stick to SOPs please). The amount of such alerts was quite impressive as a large number of the pilot population thought it was a good idea to save fuel by delaying as much as possible the LG extension and a few trainers encouraged the practice. The issue was quickly solved but it shows how easy it is to spread erroneous practices within the Industry. |
I've done one for real, the trimming for F3 after gear down is a complete non-event as is the landing. Bit odd trimming with no control feel but it really isn't a problem.
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Originally Posted by vilas
(Post 11188510)
That's true. As I said if stab is jammed only then. However many instructors teach to lower the gear after flap3 even in case of Dual RA. According to me this doesn't serve any purpose except postponing direct law by may be 15 seconds. Since you are going to fly in direct law till touchdown these 15secs should not be such a problem. According to me there are only two cases for non-standard configuration i.e. G+Y 1,2,3 and gear down and G+B gear down 1,2,3.
I have seen quite experienced 320 Captains doing anything - anything! - so they didn't have to trim the airplane manually in the sim, and here is where the problem lies: many instructors don't know how to trim the airplane using the MAN PITCH TRIM, and therefore the FO doing the sim with them learns that direct law is the "worse thing" that can happen to a pilot, starting the myth of direct law being the maneouvre that will fail your sim session. The only way I have seen to stop this is to sit in the sim with the flight crew, and flying a direct law landing myself configuring the airplane as usual: flaps 1, 2, gear (direct), and then 3. Only when they see how not difficult it actually is they start doing it themselves. And of course, if a dumb overweight Spaniard like me can do it, they can do it as well, I keep telling them! |
+1 iggy :ok:
I found there was a distinct lack of training by actual physical demonstration in all my Airbus SIMs. |
Direct law definitely feels more sensitive because there's no artificial feel added like a conventional aircraft also you move the elevator directly without any G control like in normal or alternate law. However it is not something to be afraid of, with either the stab trim available or already trimmed closely to Vapp, as when trim is not available. You are established on final course and most of the flight path will be a small straight and level and most descent to landing.
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