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A320 how to save this landing

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A320 how to save this landing

Old 8th May 2010, 01:18
  #61 (permalink)  
 
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I heard this from a former SEA colleague about this quirk in flying the scare bus. He had transitioned to the T7 and was discussing or rather giving some tips about his experience to some new A330 drivers.....he cautioned against " fighting the controls " via the side stick especially pitching motions in gusty weather when close to touchdown. According to him, if you fight the controls with pitch down inputs, the autotrim will trim down and when this cuts out below 100 ft RA as the flight control law transitions to flare law, you lose a lot of pitch authority to flare and there it goes into a crunch unless you're fast enough to take momentarily take the thrust levers out of climb detent and back to get a boost of raw power to cushion the thump. And only if there is sufficiently runway to play around with........the temporary power boost can be considerable if one is not quick enough to " retard "
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Old 8th May 2010, 02:47
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John Farley put an excellent flow chart and explanation regarding 'flight path stable' FBW aircraft and POI's --in the FT forum
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Old 8th May 2010, 11:57
  #63 (permalink)  
 
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My Twopence: Don't forget that the F/CTL system in normal law trims the aircraft 2 degrees nose down when it's in flare mode (below 50ft RA) and if back pressure is not applied to the side stick to maintain the descent path a hard landing will result.

Unfortunately when Bernard Ziegler designed the A320, he didn't put the aircraft into Direct Law during landing, so we are stuck with the feel it has with a reference pitch attitude remembered at 50 feet.
I'm amazed at that comment. Why would anyone prefer direct law for landing? Astonishing. Direct law exists because there is no flare mode in alternate law so when in alternate law due to failures direct law is entered when the gear goes down (or you have a double failure). The aircraft (if simulator fidelity is to be taken as a given) is decidedly more difficult to land in DL.

I think the root problem is the modern over-reliance on technology and automation. The A320 can be flown just like any other aircraft. Airbus itself says so. the only difference is in the F/CTL system which takes out the trim changes for the pilot in response to slat/flap, speedbrake, gear and power changes. In training young pilots to land the 320 I have lost count of the number I have to persuade to stop concentrating their scan on the PFD once they have gone visual. The focus should then be on the touchdown point with glances inside to monitor and correct speed. Keep the touch down point 1/3rd of the way up the windscreen. If it moves up you're going low; if it moves down you're going high. Correct the flight path with power adjustments as required. Simple really.
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Old 8th May 2010, 12:53
  #64 (permalink)  
 
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Why would anyone prefer direct law for landing?
Hi wingswinger,

I bet you use ground mode for take off.

It was meant to explain the difference between a conventional aircraft's feel with a quick burst of power when below 50 feet versus FBW feel.

e.g. Consider a normal 3 deg approach. If the nose was briefly allowed to drop by up to one and a half degrees (so ROD increase from 700 fpm to 1050 fpm) just as you passed 50 feet:

1) Conventional aircraft will feel correct after a quick burst of power and attitude re-established to original 3 deg trajectory.
2) A320 now uses -4.5 degs as reference attitude (despite anything done with thrust) and when below 30 feet also gradually feeds in an additional feel of 2 degs nose down. No wonder it can feel "sluggish" and "heavy" and can be very confusing.

I've spent 5 years on A320 type in intensive European Operations after over 25 years on Boeings / Lockheed. I still prefer the "feel" of a conventional aircraft, & I especially miss moving thrust levers with autothrust, & the control wheel feed back from the other pilot's input when close to the ground.

FBW is very clever in some areas - but it's far from perfect.

Last edited by rudderrudderrat; 8th May 2010 at 14:19. Reason: addition of ground mode.
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Old 8th May 2010, 13:49
  #65 (permalink)  
 
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Hello PA,

Presume that was a typo: do you mean “PIO”? Any chance of a link to John Farley’s post? Am currently on a dial-up connection at 20kb/s, so searching difficult.

A couple of years ago, when we were discussing a Lufthansa cross-wind incident at Hamburg, you may remember the subject of sidestick technique came up? My thoughts on the avoidance of “sidestick abuse”, refined in the light of comments from others, were posted here.


Back to the main topic, and Tipsy Barossa’s post. Haven’t flown the A330, unfortunately, but don’t remember ever experiencing inadequate pitch authority in the flare on the A320 in 14 years line flying, despite the features of flare law described by Wingswinger and rudderrudderrat. On an average day, if landing is assured and the speed on target, you can even retard the throttles at 50 feet, before starting the flare (as is done for certification).

Tipsy Barossa’s other point refers to the difficulty of adding a burst of extra thrust to what the A/THR is providing, but which the throttle levers − parked in the CLB detent − are not reflecting. This facility was not available in the early days, and I’m not keen on it.

By advancing the levers the slightest amount from the CLB detent, you are effectively calling for more than climb thrust. If you actually needed and achieved that much power in the late stages of an approach, you would be going around. So it’s only the relatively slow acceleration of the big fans that enables the approach to be continued, provided you quickly return to the CLB detent. On the other hand, if you return too quickly, the energy deficit may not have been corrected. It is a very crude tool, which is one of the reasons I prefer manual thrust for manual landings.

Chris
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Old 8th May 2010, 15:14
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Originally Posted by Chris Scott
Tipsy Barossa’s other point refers to the difficulty of adding a burst of extra thrust to what the A/THR is providing, but which the throttle levers − parked in the CLB detent − are not reflecting. This facility was not available in the early days, and I’m not keen on it.
... and for good reasons Chris :

This strange procedure came up only in 2004 I believe (?) through a FCOM BULLETIN :
AIRCRAFT HANDLING IN FINAL APPROACH

Above 100 feet
The purpose is to reduce the A/THR response time. This will temporarily deactivate and arm the A/THR.
"This possibility should be used in exceptional circumstances, and should not become a routine flying technique."

Below 100 feet
The story is different too, and can get pretty interesting ...

Overall, many agree that it is much more simple to be in manual thrust by 1000 feet and forget about this mascarade.
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Old 8th May 2010, 18:21
  #67 (permalink)  
 
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So are all you bus veterans saying its not practical to add power close to the ground to avoid a hard landing.....

Yes or No???

So you're at 50ft and experience perf decreasing windshear - what do you do?

Im sure its not as bad in reality as the picture you're painting
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Old 8th May 2010, 18:26
  #68 (permalink)  
 
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Hey Chris
http://www.pprune.org/flight-testing...ml#post5434108

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Old 8th May 2010, 19:43
  #69 (permalink)  
 
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Pugilistic-Would you be able to provide a link to John Farley's flow chart please?
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Old 8th May 2010, 20:15
  #70 (permalink)  
 
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http://www.pprune.org/flight-testing...l#post5432833:)

post #7
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Old 8th May 2010, 22:18
  #71 (permalink)  
 
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Reading the old version of Flying the Big Jets would answer 98% of the posts in this thread.
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Old 9th May 2010, 00:48
  #72 (permalink)  
 
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Thanks for the link, PA.

p51guy,

I'm not sure I would put it as high as 98%, but I'm not inclined to dispute your figure either. Since 1988 it's been evident to me that the A320 is a very ordinary aeropane, and handles conventionally with no particular vices.

But I agree with John Farley's comment that you need to give the relevant FBW computer a moment to correct a displacement, before chasing it yourself.

G-SPOTs Lost,

If you are using it, the A/THR normally sorts it out pretty well. If not, and you are very low, I suggest a go-around is a wiser move than trying an uncontrolled burst of thrust, followed by reversion to A/THR (see CONF_iture's post). A late switch to manual thrust is also not to be recommended.

Chris
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Old 9th May 2010, 09:31
  #73 (permalink)  
 
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@ BarbiesBoyfriend,

Instead of looking for a solution on PPRuNe, why not learn to fly?
We've all been there and done that at "our local aerodrome" - FBW is the next step in evolution.

If the Wright Brothers had started with side stick controls - how would the invention of a "big control wheel" have been greeted?

The comprehension of the pilot reflex required when converting from conventional aeroplane control to FBW is brilliantly aired on this sort of forum.
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Old 9th May 2010, 11:51
  #74 (permalink)  
 
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Hello rudder,

Ground mode of Normal Law, yes. - for about 5 seconds until flight mode has blended in. Direct Law it ain't. Next time you're in the simulator have the rad alts failed, select flap 2, put the gear down and raise the flap to 1. Fly along at about F speed and then rotate to 15 degees nose up with TOGA. That should demonstrate the difference between Normal Law Ground Mode and Direct Law.
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Old 9th May 2010, 12:03
  #75 (permalink)  
 
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Hi wingswinger,

I've flown the equivalent of "Direct Law" for over 25 years on Boeings etc. It's beautifully simple and very instinctive.
As you correctly point out
"The A320 can be flown just like any other aircraft. Airbus itself says so."

Last edited by rudderrudderrat; 9th May 2010 at 16:36. Reason: typo
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Old 10th May 2010, 18:50
  #76 (permalink)  
 
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G-SPOTs Lost,

If you are using it, the A/THR normally sorts it out pretty well. If not, and you are very low, I suggest a go-around is a wiser move than trying an uncontrolled burst of thrust, followed by reversion to A/THR (see CONF_iture's post). A late switch to manual thrust is also not to be recommended.

Chris
Thanks Chris

So an expensive possible once around again 30 minute go around instead of adding some power to arrest a decreasing performance gust of wind.

Nobodys suggesting an "uncontrolled burst of thrust" just enough to keep the desired speed whilst arresting the ROD a tad.....forgive me this is what we get paid for no?

I've never flown Airbus as you can probably tell and it cant be this bad otherwise we'd see more go arounds from Airbi, you're comments fan the flames of the accusations that FBW degrade core skills...

In many ways Im slightly flabbergasted that we're heaping ultimate speed control onto the AT in circumstances that by the sounds of it it cant always cope with, when it cant cope we're advocating a go around rather than flying the aircraft close to the ground because its unwieldy to manipulate the thrust levers
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Old 10th May 2010, 22:06
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I may (well probably ) be too far beyond my primitive knowledge level but I think the issue seems to be the transition from autothrust to manual thrust, specifically in respect to thrust levers which are not backdriven.

So, when changing to manual thrust one has to move the lever back from climb detent to find the level where the levers would have been had they been "normal" driven levers, then add power, then reduce again? Is this actually the case? Not an ideal proposition at 50ft if so...

Hence I think folks are saying that switching off the autothrottle much earlier is the way to go - keeping the PF much more "in the loop" - and not scrabbling to switch from one mode to another at the last minute.

I await correction!!
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Old 10th May 2010, 22:41
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Hi, G-SPOTs Lost,

Quote:
Nobodys suggesting an "uncontrolled burst of thrust" just enough to keep the desired speed whilst arresting the ROD a tad.....forgive me this is what we get paid for no?

I agree with most of your interpretation of my previous post, but am not entirely convinced that you understand why I’ve used the phrase: “uncontrolled burst of thrust”. If in any doubt, refer to the last paragraph of my post #69, and CONF_iture’s post #70.

As you know, on a conventional (driven) auto-throttle, a controlled, short-term thrust increase − for example, to add the right amount of energy (by increased GS) to recover from a sustained loss of headwind − is a simple matter of pushing the throttles forward, as much as you judge necessary, against the clutch mechanism. Once you’ve recovered airspeed, you allow the throttles to do their own thing again.

With the current Airbus system (unlike the A300 and A310), how much energy you add depends on how quickly the engines spool up towards the very high thrust setting you have commanded − something over which you’ve no control − and how long you dare to keep the levers forward of the CLB detent. If you overdo it, not only will you find yourself with too much energy, but the big fans will take another couple of seconds to slow down. This may result in the A/THR selecting idle, to correct an excessive IAS. Not something you want at 100ft.

As I said in an earlier post, the battle some of us putative A320 pilots waged − to persuade Bernard Ziegler that we needed conventional (driven) thrust levers, when in A/THR mode − was lost circa-1986. Our concerns included the issue of A/THR cancellation, but concentrated mainly on the loss of tactile information in A/THR with the non-driven thrust lever. The latter criticism was ruled out of order on the spurious, but undeniable, pretext that no pilot should assume that thrust is changing − without reference to the gauges − just because the throttles are moving. (I guess the B777 accident at LHR might appear to lend credence to that argument.)

Having said all that, the A320 throttle levers provide the smoothest thrust changes when operated in Manual Thrust: the best of the six jet types I flew. Left to its own devices, helped by the excellent GS-MINI system, the A/THR is also pretty good.

Chris
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Old 18th May 2010, 21:04
  #79 (permalink)  
 
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How can you guys tell the G-load on landing?
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Old 19th May 2010, 09:48
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sigler,

There's a complicated formula:

You take the average change of height of all occupants, multiplied by the square root of pi and the difference in the local elevation before and after the landing.

Or you can print a load report via the MCDU
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