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Sully's Flare on the Hudson: Airbus Phugoid Feedback

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Sully's Flare on the Hudson: Airbus Phugoid Feedback

Old 25th May 2017, 05:47
  #101 (permalink)  
 
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@Quagmire

You will note that I have removed the post that offended you, but I would say that the private comments I received were supportive.
At various times in your campaign you invited alternative views from those who you described as "Airbus apologists". Apart from the fact that I feel no need to aplogise for a very successful aircraft with one of the best safety records in the world, I am disappointed and illuminated by the fact that when such views are posted they are airily dismissed as "nonsense" or "boring"
Disappointed because on Tech Log one expects, or at least hopes, to read reasoned technical argument and counter-argument; illuminated because arbitrary rejection of opposing views without discussion is often the refuge of those who have no viable arguments of rebuttal.
But I long ago recognised the futility of arguing with closed minds, so for me the best option will be to let this thread die from neglect.

Last edited by Owain Glyndwr; 25th May 2017 at 09:17.
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Old 25th May 2017, 06:02
  #102 (permalink)  
 
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Objections many a times are visceral not technical making any discussion waste of time.
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Old 25th May 2017, 08:47
  #103 (permalink)  
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You put a catastrophic scenarios where there is none.

Oh ? I might have thought that passing 150ft at 1200ft/min approximated something a lot closer to mischief than most airline pilots routinely have to manage .. and, this, without any thrust to help out ?

By all accounts, declarer appears to have made a pretty reasonable job of the bad hands dealt to them on the day.
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Old 25th May 2017, 08:48
  #104 (permalink)  
 
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Originally Posted by CONF iture View Post
There was no such danger. Passing 150ft at 1200ft/min the airplane didn't reach yet alpha prot - Autotrim was still in action.
Had the elevators collaborated to Sully request anything better, and certainly not worse, was achievable.
You put a catastrophic scenarios where there is none.
Are you absolutely sure? From the report: 'Airbus performed a simulation of the last 300 feet of the accident flight, which indicated that the airplane was performing as designed and was in alpha-protection mode from 150 feet to touchdown.'



Honestly answer us please CONFiture, what result do you expect in a 737 with an average pilot:
-Rate of descent 1200 fpm, double the normal.
-SpeedVLS -17, that's more or less Vapp-17 in Boeing terms, leagues below the safe speed, probably approaching stall
-At or near stick shaker
-150'
-no power

Recover.
How??
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Old 25th May 2017, 08:53
  #105 (permalink)  
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As most are aware, we tolerate quite a range of robust discussion on Tech Log - barring anything which is over the top.

However, I think it appropriate to note, for those who don't know them, that OG and zzuf are, in their respective fields, peer-acknowledged technical experts.

Do this in a 737:

Thanks all the same but I think one should pass.
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Old 25th May 2017, 09:53
  #106 (permalink)  
 
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Apha-prot warning.

Whilst the experts debate each other wether you can have stall protection without phugoid damping, maybe Airbus should find a way of letting unfortunate pilots know that they have entered alpha protection?

Ultimately the only reason we are having this discussion now is the fact that Sully had no idea whatsoever that his airplane was in alpha protect mode. Maybe we do need a sidestick shaker?

Last edited by PENKO; 25th May 2017 at 11:43.
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Old 25th May 2017, 11:16
  #107 (permalink)  
 
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Maybe we do need a sidestick shaker?

Actually, I think that would be a good idea!
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Old 25th May 2017, 11:49
  #108 (permalink)  
 
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PENKO
There is already a warning in normal law which calls "speed..speed...speed" but got suppressed by priority of GPWS. Although Sully's hands were full but just like he switched on the APU out of turn had he switched off the nuisance creating GPWS he would have got the warning. May be airbus needs to address that by installing a parallel channel with another loud speaker to create safer priority for warnings.
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Old 25th May 2017, 11:55
  #109 (permalink)  
 
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Originally Posted by QuagmireAirlines View Post
So if you can't win an argument against me and the original NTSB findings, just insult your way to victory. Yeah, that works.
I guess that's one way to look at it. Another one might be that some people take any disagreement as a personal insult.
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Old 25th May 2017, 11:55
  #110 (permalink)  
 
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Exactly what I was thinking Vilas. As you say, the SpeedSpeedSpeed got suppressed due to out of sequence actions. But we can't blame Sully and Skyles for that, the situation was hectic, there was no time for a flame-out checklist designed to be read from the relative calm of level 380.

Hence the thought of an insupressable sidestick shaker/vibrator/buzzzer that unambiguously tells the pilot he's in alpha prot.
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Old 25th May 2017, 16:03
  #111 (permalink)  
 
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John,
The catastrophic scenarios was to face an all engines failure 3000 ft in the climb over a big city.
The catastrophic scenarios would have been to opt for another option ... but in the end, find yourself unable to make the desired runway ...

Originally Posted by PENKO
Are you absolutely sure?
Absolutely, as stated in the report.
  • Above 150ft the airplane was not in alpha prot.
  • Below 150ft it was.
  • And additionally passing 50ft it was not anymore.

Honestly answer us please CONFiture, what result do you expect in a 737 with an average pilot
I won't tell for the 737, not to exacerbate any passion, but we can take a 320 with a direct relation between stick and elevators displacements.
Data show that there were margin for improvements to be made at attitude and ROD levels for touchdown.
Airbus, for good reasons, put a margin between a-prot and a-max, and they did also between a-max and a-stall.
When Sully touchdowned there were still 3.5 deg to even reach a-max ...
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Old 25th May 2017, 16:54
  #112 (permalink)  
 
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Megan - "Not a FW guy, but never liked tapes. Always thought it took too much to interpret in comparison to a round dial and noting the o'clock position of the needle. Man/machine interface problem for Sully?"


Sully had 4,765 hrs in the AB. That's years of flying. I wasn't a fan of tape displays, especially for altimeters(!!), but after 4-5K+ hrs flying them I think the modern tape displays are better than round dial airspeed tapes.

I'd still might prefer round altimeters, needle straight up is also a thousand foot mark. Perhaps easier to not exceed your cleared altitude with an obvious readout (needle at 12 o'clock) vs the tape altimeter readouts.
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Old 25th May 2017, 17:03
  #113 (permalink)  
 
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Vilas - "misd-agin
Only slat attitude is very high. Even in normal landing tail strike is possible if not flared carefully. Landing distance also almost 1000mtrs higher without flaps. And you won't convince CONF iture. He has good company in Quagmire."

A post stated that AB had an ideal pitch attitude range for ditching. The range is in a previous post in this thread. The higher pitch attitude range would probably result in a tail first landing considering the tail strike regime of 11.7-13.5 degrees for a 320. So apparently a slight tail first landing, for an aircraft about to be written off, is in the ideal range.
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Old 25th May 2017, 17:03
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Originally Posted by PENKO View Post
Apha-prot warning.

Whilst the experts debate each other wether you can have stall protection without phugoid damping, maybe Airbus should find a way of letting unfortunate pilots know that they have entered alpha protection?

Ultimately the only reason we are having this discussion now is the fact that Sully had no idea whatsoever that his airplane was in alpha protect mode. Maybe we do need a sidestick shaker?


..
I'm not an Airbus guy, but isn't this signified by being in the black/yellow checker range of the airspeed?
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Old 25th May 2017, 18:40
  #115 (permalink)  
 
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Page 11 of the report, 28/213 of the PDF, goes over the airspeed display and the display symbology.

https://www.ntsb.gov/investigations/...ts/AAR1003.pdf


alpha protect and alpha max are represented by the top of the black/yellow checkerboard and the red bands.

Last edited by misd-agin; 25th May 2017 at 18:43. Reason: Alpha...
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Old 25th May 2017, 21:13
  #116 (permalink)  
 
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During the flight time in between the birds and the water impacts, the
Aircraft was flown occasionally within the alpha protection range (around 1minute 7s), notably from about 150 ft RA down to water impact.
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Old 26th May 2017, 08:31
  #117 (permalink)  
 
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Originally Posted by Vessbot View Post
I'm not an Airbus guy, but isn't this signified by being in the black/yellow checker range of the airspeed?
Yes, yet that is not clear enough apparently. Arguably the same can be said for the barberpole in a 737, hence the stick shaker/clacker...
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Old 26th May 2017, 13:30
  #118 (permalink)  
 
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Above 150ft the airplane was not in alpha prot.
Below 150ft it was.
And additionally passing 50ft it was not anymore.
This cannot be true because once it is activated, to deactivate: (from FCOM)
1. The pilot must push the stick greater than 8 degrees forward or
greater than .5 degrees for at least for .5 seconds when alpha is less than alpha max.
2. In addition below 200ft, the angle of attack protection is also deactivated when,
-the side stick deflection is less than half nose up and
-actual alpha is less than alpha prot-2 degrees.
When Sully was pulling full back stick to get flare how can he be out of alpha prot?
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Old 26th May 2017, 17:23
  #119 (permalink)  
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Originally Posted by CONF iture View Post
Had the elevators collaborated to Sully request anything better, and certainly not worse, was achievable.
Originally Posted by CONF iture View Post
When Sully touchdowned there were still 3.5 deg to even reach a-max .
Then you too agree with the original NTSB findings (and the FAA, see below) where they said flare was interfered with by the pitch-down terms by Airbus. I think its obvious. Also, note the CLmax was probably still ~5 degrees from where Sully pitched, in this case (above even the 3.5 deg margin to alphaMax). If you agree with the facts in the NTSB report such as flight data and statements they made about alpha-prot during the flare phase, then its hard to believe some others on this forum still can't see it. Its plain as day.

In summary, there is also: http://www.tc.faa.gov/its/worldpac/techrpt/ar11-28.pdf (Bilbao, 2001) "In some other incidents, crews wanted to land in a nose-high attitude (e.g., because of suspected nose wheel problems) but it was prevented by the alpha-prot feature, and the aircraft sustained preventable damage. The Mode cause code was assigned because of unsuitable control limitations imposed by the alpha-prot function."--- Although the FAA's statement about "Mode cause" isn't quite right, since its not the Mode itself, its the way the mode is constructed, which can be fixed easily in flare situations.

We've mentioned the Habsheim, Bilbao, & Hudson River A320 accidents already above, yet the recent Halifax, 2015 accident is very suspicious as well. The crew tried to pull up in time, but couldn't get the aircraft up in time. There is an accident report, yet I'm still looking for flight data plots to see if alpha-prot interfered with using the maximum amount of lift before impact close to the ground. Anybody know about that one? I do know there is a lawsuit being prepared now, so I might contact them to find out what they know about the pilot/aircraft dynamics in the moments of attempted pull-up before impact.

And I love the title of this paper, which gets to the heart of all this flare-Airbus "surprise!!!!" stuff: Sarter, N. B., & Woods, D. D. (1997). Teamplay with a powerful and independent agent: A corpus of operational experiences and automation surprises on the Airbus A320. Human Factors, 39, 553-569. Available from:
https://www.researchgate.net/publica...ountermeasures
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Old 26th May 2017, 20:11
  #120 (permalink)  
 
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Quagmire, Halifax was due to pilots forgetting to fly the aircraft, rather than just watching the automation. It had nothing to do with the aircraft protections..If they did pull up it would have been load factor protection to +2g as the flaps were out, and this protection is using the aircraft certified limits as a target. I do wonder what you are trying to prove with your discussion of the protections, or is it data gathering for a law suit?
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