Question on - Sully's: Hudson ditching

[bobdazzle]

Why did the airplane keep afloat even hours after the ditching inspite of it's packs, outflow valves not being closed during the ditching process?

[Intruder]

Lots of air in the cabin, with no exhaust outlet up high.

Why does a bathyscaphe or bathysphere work?

[Gulfstreamaviator]

big aid....to flotation
glf

[HPbleed]

I thought the valves were closed? Skiles hit the ditching pushbutton did he not? Although it made little to no difference as the high sink rate in the last milliseconds ripped the rear fuselage which allowed water to ingress at the rear.

[Lyman]

Sure? The tail was badly damaged, I am not sure the metal was broken open, and I am pretty sure the hull was intact, eg, the aft bulkhead was not holed.

I think the wings had alot to do with the flotation. The fuel helped, but the voids in the wing provided a good deal of buoyancy. Besides, any modern a/c is pressurized, and designing a device that keeps air in will probably keep water out? The fit on the skin is designed to be tight, since any "leakage" of air, no matter where, means 'drag'? Even the interior penetrations for cabling, ducting and plumbing are sealed, not so much to make her watertight, but to prevent abrasion, and wear on the interior hull.

Not to mention coating the entire a/c with Paint, to lessen drag, an additional benefit would be "watertight". The 1500 pounds of resin/paint have to perform beyond their dead weight, else paint would not be used.

The injured FA was said to have been in knee deep water, at the aft door. I think this intrusion was from the open door, which was then closed? All things considered, an a/c like the 320 is a better boat than alot of boats.

[PJ2]

HPBleed: Although it made little to no difference as the high sink rate in the last milliseconds ripped the rear fuselage which allowed water to ingress at the rear.

Lyman: Sure? The tail was badly damaged, I am not sure the metal was broken open, and I am pretty sure the hull was intact, eg, the aft bulkhead was not holed.
The rear fuselage was significantly damaged as shown in the "Structures 7F Addendum (http://dms.ntsb.gov/pubdms/search/document.cfm?fileid=419640&ntsbnum=DCA09MA026). The NTSB Report is at: http://www.ntsb.gov/doclib/reports/2010/aar1003.pdf

At the site where the Structures document is found, the entire Docket can be accessed for further reading.

PJ2

[Um... lifting...]

Bathyscaphe float is full of gasoline for buoyancy, the descent weights (shot) are jettisoned by electromagnet for ascent, and trim is achieved by substituting seawater for gasoline in the buoyancy tank.

Truly the design of a mad genius.

[lomapaseo]

Bathyscaphe float is full of gasoline for buoyancy, the descent weights (shot) are jettisoned by electromagnet for ascent, and trim is achieved by substituting seawater for gasoline in the buoyancy tank.

Truly the design of a mad genius.


Tis true and a small amount of air trapped in a battery compartment vent tube can be disasterous while submerged

[Ollie Onion]

Surely the fuel kept it afloat, not long after departure the wings would have had a significant amount of fuel in them. Fuel is not as dense as water so in effect you have two massive floatation devices keeping the rest of the aircraft above water.

[Chu Chu]

Sure, fuel is less dense than water, but air is less dense still. So empty fuel tanks would have contributed more buoyancy than full ones. I suppose the bathyscaphe float was filled with gasoline so that it could be exposed to external pressure without compressing. Not a problem for an airplane, at least as long as it stays on surface . . .

[HPIC]

Since they were only going about 500nm on that flight, they probably only had 6.5 to 8T on fuel(depending on alternate) on board at takeoff, well under half of max, which means the fuel tanks had mostly air in them.

[galaxy flyer]

Fuel in the tanks, being an incompressible fluid, should have increased the strength of the structure. Possibly being a bigger advantage than having damaged empty tanks.

Skiles didn't activate the ditch switch, IIRC

GF

[Dan Winterland]

Aircraft are quite bouyant and can float for a while. The RAF nimrod which ditched in the Moaray Forth in the late 1990s floated for some hours and a 707 which landed in lake Victoria floated for three days.

The ditching button will close all the holes on the 320, but the heavy engines should come off as well. The 'fuse pins' have a relatively weak breaking point in the event of a aftwards shock and they would normally come off on ditching. on Sully's aircraft, one came off. It's possible, the very low touchdown speed he acheived didn't rip both off. Also the high nose attitude meant the tail touched first casing the breach in the rear cabin.

[barit1]

#1 engine parted company at touchdown, and that side was more bouyant than the other. When "docked" on the Manhattan waterfront, the right wing slowly sank while the left rode high in the water.

The #1 engine was later recovered from the river bottom.

[Lyman]

Hi barit1. #1 fell off the wing, but not at touchdown, I think. From the Harbor master video, a pronounced Yaw left whilst skidding across the water indicates the engine was dislodged, and perhaps presenting more drag than normal. Then, when a/c stopped, the engine fell free.

That is from memory, so use a pound of salt, eh. :ok:

[barit1]

Yeah, I suppose that's possible, though I wouldn't have guessed it.

[Cubs2jets]

Jeff Skyles NOT pressing the "Ditch Switch" had absolutely no affect on the sinking of 1549. Pressing the switch would have closed the two outflow valves on the Aft Pressure Bulkhead. The fact that nearly 25% of the APB was ripped out negated his actions or lack there of.

The aft cabin flooded up to a depth of about 5ft (~2.2m) within minutes of coming to a stop (last row of passengers were 3ft ((1m)) deep within 60 seconds). The forward cabin remained relatively dry for a much longer period of time. The cabin was "habitable" for about 30 min after the ditching. The aircraft remained technically afloat for 22 hours before completely submerging (all except the left wingtip). Yes, it was right wing heavy due to the loss of No.1 engine. It didn't sink further because the right wingtip was stuck in the riverbottom.

The main source of bouency was the fuel in the tanks (and a bubble in the crown of the cabin). That fuel slowly leaked out through fuel lines and punctures solwly allowing the aircraft to sink.

C2j

http://i272.photobucket.com/albums/jj200/Cubs2jets/1549Aftpressurebulkhead.jpg

[Lyman]

@Cubs2jets

"Jeff Skyles NOT pressing the "Ditch Switch" had absolutely no affect on the sinking of 1549. Pressing the switch would have closed the two outflow valves on the Aft Pressure Bulkhead. The fact that nearly 25% of the APB was ripped out negated his actions or lack there of."

The aft Pressure Bulkhead is effectively in two parts, above the floor, and below it. The dump valves communicate with the cabin, the damaged portion with the hold. If the APB (cabin portion) was undamaged, and not leaking into the cabin, the open valves would allow water ingress. If the valves had been closed, there would have been less water in the cabin, and the a/c would have remained afloat longer, No? Or, are we looking through the APB directly into the cabin and looking at a seat?

Bottom Line? Should the valves have been closed by crew? Yes.

[Cubs2jets]

I think it is pretty clear in the picture that the APB is essentially one unit that encompasses above and below the floor, not two parts one above and one below the floor.

Inside the pie section labled "Damaged Bulkhead" on the picture you are looking through the APB at the backs of the galley cabnetry located on the forward side of the APB. The bottom of the white structure is the floor level (cabin/baggage seperation). This is a massive breach of the APB. Closing the two outflow valves with the "Ditch Switch" would have made little or no difference in keeping water out of the cabin.

C2j

[Lyman]

"Closing the two outflow valves with the "Ditch Switch" would have made little or no difference in keeping water out of the cabin."

I don't disagree. :ok:

[lynn789]

it seems that no airliner simulators have a ditching program??

[Chu Chu]

Kind of makes you wonder if the ditch switch has a point. Sully ditched about as gently as it would be possible to do, yet the bulkhead was damaged enough to make closing the outflow valves irrelevant.

[sabenaboy]

Kind of makes you wonder if the ditch switch has a point.

The ditching switch is useful! I use it a few times per year!! :O No kidding!

[3holelover]

@Cubs2Jets,
Those are not "outflow valves", in the picture you posted, but pressure relief valves on the pressure bulkhead. The (single) outflow valve on an A320 is mounted on the fuselage further fwd, just behind the aft bulkhead of the bulk cargo area. Those two relief valves shown, would in all likelihood have remained closed.
The ditching switch (which was not used) would have closed the two fwd avionics cooling valves as well as the outflow valve.

Personally, I wonder if water rushing in the open outflow vlv during ditching might have had something to do with the damage to the aft pressure bulkhead?

In any case, the aircraft floated because of all the air in the wings. The fuel tanks vent out the bottom, so the air was trapped.

[Pub User]

Sully ditched about as gently as it would be possible to do,

I don't think so. I recall reading somewhere that he hit the water at a considerably higher speed and rate-of-descent than he would have liked, in order to land in a stretch of water clear of bridges and vessels.

No criticism. It was a great job, and touching a bridge or ship would have changed the story completely.