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Ditching a modern airliner

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Ditching a modern airliner

Old 3rd Mar 2019, 13:12
  #41 (permalink)  
 
Join Date: Aug 2011
Location: Australia
Posts: 373
With all due respect, by flying an approach to ditch has very little to do with visuals (in a simulator).
A night ditching has its own hazards. You won't see the water until the landing lights illuminate it. So in the simulator you don't have to rely on the visual scene to judge when to flare. In fact you may as well switch off the visuals to simulate a black night. The skill is in the instrument flying bit. To allow for altimeter error you need to be fully configured and on speed early.
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Old 3rd Mar 2019, 13:26
  #42 (permalink)  
 
Join Date: Sep 2016
Location: USA
Posts: 433
Originally Posted by Winemaker View Post
Re simulator training, since the simulator can't generate more than one g how does the experience translate to actual flying? As an ex formula car racer I've experienced more than 2 g lateral load for extended periods of time; a simulator can't generate the head/neck loading and wind impact of the real deal. When flying the g load is generally vertical through the seat so I guess very short bumps above 1 g could be made. What I'm asking, as SLF, is how effective the simulator is at representing real flying conditions.
For regular maneuvering, the lack of G in the sim is not a factor. In a 30 deg banked turn, (which is more than what you see the vast majority of the time) the G is 1.15, which doesn't feel appreciably different from 1. So you don't notice anything.

Rolling into and out of 45 degree banked turns (1.4 G's) the lack does throw me off a bit, but it's a minor distraction.

The real difference comes in a dive pullout after a stall or unusual attitude recovery, and there's nothing that can be done about that.
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Old 3rd Mar 2019, 14:26
  #43 (permalink)  
 
Join Date: Jul 2007
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Wikipedia has just 24 articles on airliner ditchings.

https://en.wikipedia.org/wiki/Catego...lving_ditching
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Old 3rd Mar 2019, 15:45
  #44 (permalink)  
 
Join Date: May 2014
Location: In thin air
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Originally Posted by dogcharlietree View Post
Please remember that the main problem in a ditching is impact forces.
So doesn't the old equation E=mv2 come into play. If you double the speed at impact then you have four time the impact forces.
The impact forces are primarily a function of the rate of descent at touchdown. With unlimited runway length the flight speed is far less important. More important is the optimum pitch attitude, which will dictate the horizontal speed at impact.

Part of the problem is that manuals may provide a procedure for all engines out, and a procedure for ditching. The ditching procedure supposes that you can maintain a certain speed and control the vertical speed with engine thrust. With all engines out you cannot maintain VREF40 and 200 - 300 fpm. Your rate of descent will be more like 500 - 600 fpm. That means that the normal approach speed is too low for a successful flare to ideally zero fpm rate of descent. You need to carry some extra speed during the approach that you then bleed off at low height and minimal vertical speed.

Someone asked if model ditching test are done with airliners. Yes, they are required for certification of transport airplanes approved for long overwater flights.

Last edited by Gysbreght; 3rd Mar 2019 at 15:51. Reason: Typo and added text
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Old 3rd Mar 2019, 17:30
  #45 (permalink)  
 
Join Date: Jan 2006
Location: US
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Originally Posted by Gysbreght View Post
The impact forces are primarily a function of the rate of descent at touchdown. With unlimited runway length the flight speed is far less important. More important is the optimum pitch attitude, which will dictate the horizontal speed at impact.

Part of the problem is that manuals may provide a procedure for all engines out, and a procedure for ditching. The ditching procedure supposes that you can maintain a certain speed and control the vertical speed with engine thrust. With all engines out you cannot maintain VREF40 and 200 - 300 fpm. Your rate of descent will be more like 500 - 600 fpm. That means that the normal approach speed is too low for a successful flare to ideally zero fpm rate of descent. You need to carry some extra speed during the approach that you then bleed off at low height and minimal vertical speed.

Someone asked if model ditching test are done with airliners. Yes, they are required for certification of transport airplanes approved for long overwater flights.
A ditching is a ditching. The difference is with power or without power? Obviously with power should be easier. Without power your rate of descent at touchdown does not have to be 500-600 FPM. You can make it as smooth as a normal touchdown if the sea state is fairly calm. You just need to maintain excess speed and trade that off, in the flare, until you're approaching the desired touchdown speed. With waves the equation to do it becomes much more difficult.

The reason US 1549 hit so hard in the Hudson is because Sully had run out of airspeed at over 100' AGL and was AOA limited. From that point on the AOA limiter prevented a stall but the lack of available airspeed (AOA) prevented any attempt at flaring to reduce the rate of descent at water impact.

The US 1549 investigation mentions using excess airspeed and converting that into a flare to reduce impact forces. Guys have to figure this out beforehand because there's no ability to regain airspeed at low altitude once you squander your airspeed and you have no power available.

Last edited by misd-agin; 3rd Mar 2019 at 17:31. Reason: added word
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Old 3rd Mar 2019, 18:24
  #46 (permalink)  
 
Join Date: May 2014
Location: In thin air
Posts: 186


You've got it
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Old 4th Mar 2019, 05:40
  #47 (permalink)  
 
Join Date: Jan 2013
Location: Australia
Age: 51
Posts: 168
Originally Posted by fireflybob View Post
As regards lifejackets as a passenger I'd still like to have one just in case!
This is also probably the main reason. It gives SLF hope. Bit like the crews of various cold war bomber aircraft (particularly those in the pit below or behind the cockpit). No bang seats like the pilots but parachutes and an escape door - very slim chance of successful use if the aircraft was going down, but at least a slim chance is better than none.
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Old 4th Mar 2019, 16:46
  #48 (permalink)  
 
Join Date: Jul 2000
Location: Nirvana..HAHA..just kidding but,if you can tell me where it is!
Posts: 333
For all the big Boeings,as you have no time to go for a checklist if you hoover up Jonathan Livingstone and his cousins at 2,500' on take off,.ex Dubai,Maldives,Seychelles,Nosy Be,etc..

OPO U30 BFA,.....basically,everything covered by the ditching checklist,below 5000'

O override on Gear n Terrain(least useful item but kills the warning)
P packs off
O outflow valves closed(very good idea,this one)

U undercarriage up
30 Flap 30

B Through in a "Brace Brace"..............now the lucky bit,,and once in the water

F fuel control switches to cutoff
A Apu switch,pull

Throw in the perfect manoeuvre to parallel the swell therebye avoiding smacking in to a crest,and..hey presto,there you have it,the perfect ditching...

IN YOUR DREAMS!




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Old 4th Mar 2019, 19:23
  #49 (permalink)  
 
Join Date: Aug 2004
Location: southwest
Posts: 209
At my initial SEP when I joined easyjet it was explained that " a ditching was very unlikely because we don't fly over sea much"

I mentioned that a friend of mine had ditched a large aircraft just off the scotish coast due to fire and my last employer almost put and a/c in the sea off jersey by putting both props to feather instead of cruise.

You don't have to be mid Atlantic or lose both engines to end up in the drink!
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