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757 pilot had history of hairy landings

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757 pilot had history of hairy landings

Old 30th Aug 2020, 10:37
  #61 (permalink)  
 
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Originally Posted by Uplinker View Post
If, owing to a quirk of physics, our cars veered to the right with increasing speed, and to the left with decreasing speed...
That is exactly how a motorcycle and sidecar configured for the right side of the road behaves.
  • The faster you go, the more the sidecar drags you towards the near side of the road.
  • Under acceleration the sidecar tries to make you spear off the road.
  • Under brakes the sidecar tries to steer you into oncoming traffic.
To mitigate these effects, the bike is leant slightly away from the sidecar and the sidecar wheel is toed in significantly towards the bike, but this only helps,it certainly doesn't come anywhere near eliminating the joys of riding a sidecar.

And now your comments have me wondering whether it would be possible to dynamically adjust these "trim" conditions at least for different speeds.
Or I could just keep a safe distance from my friend's sidecar. My inner engineer is finding it difficult to resist getting involved, even as the bit of my brain that tried to ride one 39 years ago is howling in protest.

Last edited by nonsense; 30th Aug 2020 at 16:14.
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Old 30th Aug 2020, 10:40
  #62 (permalink)  
 
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Brilliant !
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Old 30th Aug 2020, 12:48
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Can you explain how does it compensate for thrust changes.
Two different effects with thrust changes:

* Pitch/power couple is almost entirely removed through software on a fly-by-wire aircraft.
* The 777/787 will pitch to maintain airspeed with a power change - add power, pitch will gradually increase to maintain the trimmed speed and vice-versa. An Airbus (with plain old C* law) will maintain flight path at the expense of speed until another limit in the flight path envelope is reached.

Personally I prefer the stability of the Airbus - on a gusty day with significant speed changes the flight path on approach tends to be nailed. Speed changes on a Boeing result in flight path changes.
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Old 30th Aug 2020, 15:44
  #64 (permalink)  
 
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Personally I prefer the stability of the Airbus - on a gusty day with significant speed changes the flight path on approach tends to be nailed. Speed changes on a Boeing result in flight path changes.​​​​​​
I was writing on another thread about runway excursions in India. They are exclusively happening in 737 800. Although a good pilot is expected to handle any aircaft safely and within it's limits but those who are borderline not so adept appear to have problem maintaining the flight path lower side of approach after AP disconnection. They are crossing threshold between 100 and 150ft. speed +10 which doesn't appear bad but adds to landing distance, tailwind and prolonged flare resulting in overruns. Actually there are more A320s in India than 737s but they don't seem to have problem. Basic induction into both Aircaft is from the same common stock 250hrs CPL to start with then into command in due course.
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Old 30th Aug 2020, 16:36
  #65 (permalink)  
 
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Originally Posted by vilas View Post
Can you explain how does it compensate for thrust changes. In speed stable system if thrust is increased and if the flight path is maintained i.e. if the nose doesn't come up speed will increase. Similarly if the thrust is decreased if the nose doesn't drop speed will decrease. That's what happens in Airbus. What happens in 777?
It "compensates" as in, prevents the thrust couple from changing the speed maintained hands off.

It does not "compensate" as in, prevent the attitude from changing; this would, of course, vary the speed and go against the fundamental point of the control law (and would essentially turn it into the Airbus control law, as you note)
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Old 30th Aug 2020, 20:41
  #66 (permalink)  
 
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Originally Posted by vilas View Post
Can you explain how does it compensate for thrust changes. In speed stable system if thrust is increased and if the flight path is maintained i.e. if the nose doesn't come up speed will increase. Similarly if the thrust is decreased if the nose doesn't drop speed will decrease. That's what happens in Airbus. What happens in 777?
It's FBW. On the 737, if the thrust changes, the pitch/thrust couple is affected and a pitch input is required to maintain the flightpath. Any sustained pitch force will need to be trimmed out. The FBW on the 777 compensates for the pitch/thrust couple when the thrust changes. A trim change isn't needed because the FBW deals with the control force that would otherwise be required. When climbing, flying level or descending at a constant speed, assuming the aircraft is trimmed to the reference speed, there will be no control force to hold irrespective of thrust. If the reference speed changes, it will produce a control load which will need to be trimmed out. It is easier to use in practice than a paper explanation would suggest.

Last edited by spanner the cat; 31st Aug 2020 at 06:53.
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Old 30th Aug 2020, 23:09
  #67 (permalink)  
 
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My basic understanding of Boeing's FBW is that you don't touch the trim switches unless you need to change your airspeed.
​​​​
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Old 31st Aug 2020, 22:31
  #68 (permalink)  
 
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Originally Posted by Check Airman View Post
The article said the captain should have intervened earlier. How’s one supposed to train or evaluate a student on landings if intervention is done at the first sign of trouble?

When training a new Line Check Airman I have a :45 minute brief I give called, “Verbally Managing the Landing.” (A319/320 - when training new Bus pilots I give a trainee version of this brief to them. This will familiarize them with the commands I will state in the landing phase and their expected appropriate response)

50’ AGL is where the start point of the brief and the selection of reverse is the end point. I identify gates, trainee action or inaction, verbal check airman commands (One - two words, easily said, easily understood), trainee response correct or incorrect and then further check airman verbal commands or, most likely, take over. Anticipation underpins all. (Obviously with no yoke, there’s no tactile nor visual feedback, that’s tough for a new check airman, one has to think about the landing phase differently when teaching IMHO)

You are correct you don’t have to intervene “at the first sign of trouble.” (Unless late in the landing phase) But I have found in almost all cases you should intervene at the second sign of trouble.

my 2¢.


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Old 31st Aug 2020, 23:07
  #69 (permalink)  
 
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There's actually a silver lining to the lack of connection between the controls on both sides of an Airbus. It is that, unless they hear "DUAL INPUT" (or "I have control" if things go south far enough), the trainees can be totally certain that it was them and only them at the controls all the way through. In this way, it's a bit more clear-cut what works and what doesn't. In an aircraft with proper dual controls, some instructors may do subtle interventions on their side without later explaining that to the trainee - and, hence, the trainee can be left with a somewhat flawed impression of what needs to be done because he doesn't factor in that subtle, unmentioned input from the instructor.

That's the glass-half-full viewpoint though. The glass-half-empty one is that teaching and intervention indeed become more difficult and are well worth some dedicated discussion during LTC/TRI training (and, if you ask me, during every Airbus pilot training as part of the pilot incapacitation topic). The standard rules for taking over in the event of suspected incapacitation are not always safe enough close to the ground as you might not have the time to wait for a response to two consecutive deviation callouts. Conversely, if you always take control as soon as anything deviates from normal, that may be detrimental to the trainee's learning. It can be a tough call - and one that only comes with experience.
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Old 1st Sep 2020, 02:14
  #70 (permalink)  
 
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Originally Posted by Fursty Ferret View Post

Personally I prefer the stability of the Airbus - on a gusty day with significant speed changes the flight path on approach tends to be nailed. Speed changes on a Boeing result in flight path changes.
Both concepts work but the Airbus is steadier. Point and let go... auto thrust off to stop the ridiculous power up, power back, power up, power back....ad nauseum, and the plane just tracks towards the aimpoint even in gusty winds.
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Old 1st Sep 2020, 11:13
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So essentially Airbus FBW aircraft fly like any other



Airbus FBW aircraft
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Old 1st Sep 2020, 12:32
  #72 (permalink)  

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Originally Posted by stilton View Post
So essentially Airbus FBW aircraft fly like any other

Airbus FBW aircraft


But then, after all, it will fool a human exactly the same as the 757 discussed above: https://assets.publishing.service.go...DHJZ_12-08.pdf
“THE FLARE WAS RATHER LATE THERE……..BUT THEN I SHOULD HAVE TAKEN OVER”.
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Old 2nd Sep 2020, 05:43
  #73 (permalink)  
 
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Originally Posted by misd-agin View Post
Both concepts work but the Airbus is steadier. Point and let go... auto thrust off to stop the ridiculous power up, power back, power up, power back....ad nauseum, and the plane just tracks towards the aimpoint even in gusty winds.
Auto thrust off? In Gusty winds? That's not what airbus wants.
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Old 2nd Sep 2020, 07:53
  #74 (permalink)  
 
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But then, after all, it will fool a human exactly the same as the 757 discussed above:
Let's accept that the wonderful Airbus has an Achilles's heel in training a specially ungifted trainee about flare perception. So if trainer keeps flaring then trainee doesn't learn and if he doesn't then that can become the last landing before major maintenance. Also fracture of his disc is the least exciting thing a passenger is looking forward to. So since he has very poor judgement some safe guards have to be in place. He should not be executing the flare if the AC is not correctly placed with proper ROD at least from last 100ft. Any corrections required should be done by the trainer and then hand over for flare and landing. The second safe guard is at twenty feet RA call. Somebody needs to flare if not the trainee then the trainer himself. A small backward movement of the stick even without take over button and release will break the descent and touchdown anything around 400ft/mt. should be OK(no choice). Last every body doesn't have to be a pilot. May be the world is missing a genius in another field.
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Old 2nd Sep 2020, 08:47
  #75 (permalink)  
 
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Originally Posted by misd-agin View Post
Both concepts work but the Airbus is steadier. Point and let go... auto thrust off to stop the ridiculous power up, power back, power up, power back....ad nauseum, and the plane just tracks towards the aimpoint even in gusty winds.
(my bold)
Not sure what you mean here. With auto-thrust off you still follow the magenta speed bug right?.......which on approach is indicating ground speed mini.......which reacts to wind gusts.

So if the auto-thrust is going up and down 'ad nauseam' to follow the bug speed, then so should you be if you use manual thrust.

Boeing has a different way of calculating the approach speed, and you shouldn't substitute the Boeing method in the Airbus.

If you ignore Airbus ground speed mini you could end up in a very sticky situation.
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Old 2nd Sep 2020, 15:54
  #76 (permalink)  
 
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Originally Posted by vilas View Post
Auto thrust off? In Gusty winds? That's not what airbus wants.
Not what Airbus wants but much smoother controls and manual thrust does a much nicer job in gusty conditions than the A/THR does. A/T works well in certain situations, but find it really can't compete with manual control on gusty, sheery days. It can get out of sync with the gusts and start an almost PIO type inputs. Much simpler to just fly it manually.

And also fully in compliance with Airbus' golden rules and principals of "If it's not doing what you want take control", and "use the appropriate level of automation for the task at hand".
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Old 2nd Sep 2020, 16:17
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And also fully in compliance with Airbus' golden rules and principals of "If it's not doing what you want take control", and "use the appropriate level of automation for the task at hand"
You find problem with ATHR or the GSmini itself?
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Old 3rd Sep 2020, 00:27
  #78 (permalink)  
 
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Originally Posted by Uplinker View Post
(my bold)
Not sure what you mean here. With auto-thrust off you still follow the magenta speed bug right?.......which on approach is indicating ground speed mini.......which reacts to wind gusts.
Yes, but GS Mini minimises the need for big thrust changes.
A positive gust increases your IAS, but the Vapp target increases as well. Only a small thrust increase should be required to compensate for the extra headwind.
A negative gust decreases your IAS, but the Vapp target decreases as well.

I think that misd-agin is referring to the A/THR overcorrecting in gusty conditions. Which it does. With the risk of reducing or adding too much power just before or during the flare.
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Old 3rd Sep 2020, 00:39
  #79 (permalink)  
 
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Originally Posted by vilas View Post
Auto thrust off? In Gusty winds? That's not what airbus wants.
Airbus states that A/THR should be used, not shall.
They also state that the A/THR should be disconnected in case of unsatisfactory performance. Chasing the speed or overcorrecting can be seen as unsatisfactory performance. It would be the case for a trainee or a pilot being checked, so why wouldn’t it apply to the automation?

Everyone has their preference, and I agree that it’s easier to land without the A/THR making excessive thrust changes.
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Old 3rd Sep 2020, 08:48
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My experience is that GS-mini more or less eliminates “hunting” by the auto thrust in gusty conditions. I used to fly regularly without auto thrust at my previous operator and I’m embarrassed to say that it usually did a better job than me. I think I’ve flown one approach without auto thrust in the last eight years, and that was only because it was decided that VLS-5 was its new favourite speed, in an A321 at max landing weight and conf 3.

The 787 auto thrust, on approach, is excellent in my opinion. It obviously biases speeds above vref, but in general is completely reliable and unobtrusive. The exception is on intermediate approach when it frequently seems to forget that it’s responsible for the speed control during level-off, even with the speed trend arrow going well south of the bugged speed.
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