US Airways Jet crashes in Hudson River

[n122vu]

Pilot's Eye View of the NYC Crash Flight

http://news.bbc.co.uk/2/hi/7834499.stm

Looks like FSX, simulation video created by Just Flight.


[Moderator note: merged with the existing thread]

 

[Moonwalker]

Although it possibly could be trained without being a glider, I do believe it actually helps.

Yes. And commercial pilots actually don't train ditching. Some just train gliding in the simulator. Being a glider may contribute to a safe ditching. But I also think that very experienced pilots can bring their aircraft down safely without being a glider (but I'd say that the majority of experienced commercial pilots are also experienced private pilots anyway).

Each aircraft has a specific value which says from which altitude the aircraft can still fly a certain distance without any power if the aircraft maintains a certain speed (even a 747 or an A380 can, it's a myth that airplanes fall down like stones just because the engines are lost). And the landing, be it on water or on solid ground, actually is not that much difficult too. The only critical thing is to find a suitable spot. The Hudson River just was the most perfect spot to put the A320 down relatively safely. Just like the airport in Gimli was perfect too for Air Canada Flight 143. But without the Hudson River and the Gimli airport in place, well... imagine yourself, especially downtown New York.

 

[Andy44]

Everything in that article attributed to glider pilots is taught to all pilots, not just gliders. In the event you lose engine power, you should immediately pitch to obtain best glide speed, which is known for every airplane and is in the operator's manual. While you're getting to best glide speed, start looking for a place to land. Start maneuvering the aircraft to execute your plan. Restart the engine once you have a handle on your airspeed, if possible. Finally, transmit a mayday call.

Aviate, navigate, communicate, in that order. Meaning: get control of the aircraft (airspeed), figure out where you are and where you are trying to go, then talk on the radio once you've got a free moment.

I think a glider pilot would have an advantage in energy management during his approach, though, since he does it all the time, but every pilot is taught how to sideslip and forward slip to bleed off energy while managing cross winds, even if it's not normal in a jetliner, and nobody starts pilot lessons in jetliners.

Experience and training is key. This guy is a Phantom pilot. If anything glides worse than an A320, it's a Phantom, the Powered Brick.

 

[SiberianTiger]

A proposed A-320 mod for US Airways:

 

[Linguofreak]

Everything in that article attributed to glider pilots is taught to all pilots, not just gliders. In the event you lose engine power, you should immediately pitch to obtain best glide speed, which is known for every airplane and is in the operator's manual. While you're getting to best glide speed, start looking for a place to land. Start maneuvering the aircraft to execute your plan. Restart the engine once you have a handle on your airspeed, if possible. Finally, transmit a mayday call.

Aviate, navigate, communicate, in that order. Meaning: get control of the aircraft (airspeed), figure out where you are and where you are trying to go, then talk on the radio once you've got a free moment.

I think a glider pilot would have an advantage in energy management during his approach, though, since he does it all the time, but every pilot is taught how to sideslip and forward slip to bleed off energy while managing cross winds, even if it's not normal in a jetliner, and nobody starts pilot lessons in jetliners.

Experience and training is key. This guy is a Phantom pilot. If anything glides worse than an A320, it's a Phantom, the Powered Brick.

You make it sound like the A320 glides badly. If a plane has too bad of a glide ratio it won't be fuel efficient enough to be economical as a jetliner.

The sources I'm finding say that it has a glide ratio of 17 or 18 to 1, which is about as high as any other jetliner. There are very few powered aircraft with higher glide ratios. You have a few things like the U-2 and some of your planes built to break distance records, but otherwise the only thing with a higher glide ratio than a jetliner is a glider.

I also looked up the Phantom, and its glide ratio surprised me, given its reputation as a brick: 8.58, which is actually apparently better than house sparrows and some general aviation aircraft.

 

[Andy44]

Well, I was comparing the A320 to sailplanes, but I see how I worded it might be confusing.

 

[Urwumpe]

Lingofreak: You are a bit wrong: It is good for planes to have a bad glide ratio. If you want to have fast planes, where the lift generated is naturally a few magnitudes lower than the drag. An A320 can be a very effective plane, by having a suboptimal glide number, so inductive drag at high speeds is less of an concern.

A phantom is a bad glider, because it is designed to fly supersonic. Just like the Shuttle is a brick, because it is designed to reenter from space in first place and just barely land in one piece in second place.

 

[Linguofreak]

Lingofreak: You are a bit wrong: It is good for planes to have a bad glide ratio. If you want to have fast planes, where the lift generated is naturally a few magnitudes lower than the drag. An A320 can be a very effective plane, by having a suboptimal glide number, so inductive drag at high speeds is less of an concern.

Sure, a jetliner may be designed to sacrifice some of its glide ratio for speed, but fuel efficiency is a big consideration for jetliners, and, as such, glide ratio is more of a concern for them than for any aircraft type other than gliders. Thus they have nearly the highest glide ratios of any powered aircraft.

A phantom is a bad glider, because it is designed to fly supersonic. Just like the Shuttle is a brick, because it is designed to reenter from space in first place and just barely land in one piece in second place.

Well, the Phantom isn't an entirely terrible glider. It's glide ratio isn't great (about half that of a jetliner), but looking at the numbers, it's better than I'd expected. But fuel efficiency isn't a big concern for it (fighting capability is the bigger concern), so glide ratio was not high on the list of priorities for its designers.

And for the shuttle, what it's trying to do during reentry is to slow down. So the glide ratio should only be high enough to provide the cross-range desired.

 

[cjp]

This glide ratio made me think...

Suppose you design a jetliner such that it has a very good glide ratio, comparable to a glider. Only, you give it powerful jet engines that allow it to go as fast as other jetliners.

What happens when you accelerate such a plane beyond the speeds of a glider? Both drag and lift will increase. You can increase the altitude of the plane, so you start flying in lower density air. Both lift and drag decrease. This continues until lift equals weight. By speeding up more, you can climb more, until the engine force equals drag at cruising throttle.

The only reasons I can see why a jetliner can't have such a good glide ratio are:

• Maybe drag at jetline speed and altitude has increased cmp. to glider speed+altitude, requiring stronger wings & so on, requiring a heavier airplane.
• Maybe an aerodynamically efficient design for jetline speed+altitude isn't optimal for glider speed+altitude.
• Maybe a glider design is far from optimal for passenger transport, even when taking fuel economy into account.

 

[Urwumpe]

You have to remember that the Glide number is only valid for the optimal gliding speed. If you optimize the gliding behavior for jet liner cruise speed, you also need to drop steep enough to sustain this gliding speed.

 

[cjp]

You have to remember that the Glide number is only valid for the optimal gliding speed. If you optimize the gliding behavior for jet liner cruise speed, you also need to drop steep enough to sustain this gliding speed.

Yes, but 'steep enough' is determined completely by the glide number. With a good glide ratio, your drag is very low, so you hardly have to dive to compensate for loss of speed, even when your speed is high. So, once you have a good glide ratio, the steepness of your descend is already no longer a problem.

In the US Airways crash, the jet was probably below its optimal gliding speed when it hit the geese (although I'm not really sure). So, initially, the first thing it had to do was descend steeply. In a later stage, I think the descend was faster, but less steep.

BTW, how does the glide ratio usually change with altitude (air density, temperature etc.) and speed?

 

[Urwumpe]

BTW, how does the glide ratio usually change with altitude (air density, temperature etc.) and speed?

I had it in a book about high-performance aircraft... maybe I can find the information again...

If I remember correctly, it was a pretty complex formula, if you include the airfoil function into it. Otherwise, it is just Lift/Drag, which depends always on the current flight state. The maximum Lift/Drag ratio is a even more complex term.

 

[Linguofreak]

You have to remember that the Glide number is only valid for the optimal gliding speed. If you optimize the gliding behavior for jet liner cruise speed, you also need to drop steep enough to sustain this gliding speed.

True, but, as a rule of thumb, if you improve your glide ratio (which is your lift/drag ratio at glide speed), you also improve your lift/drag ratio at cruise speed. So a good glide ratio is still important for fuel efficiency. And if a plane loses power while cruising, it can simply fly straight and level until it reaches its glide speed.

In any case, the numbers speak for themselves, as jetliners have higher glide ratios than pretty much any modern powered aircraft.

 

[Urwumpe]

In any case, the numbers speak for themselves, as jetliners have higher glide ratios than pretty much any modern powered aircraft.

Yes, but also at least three times lower glide ratios as a high performance gliders. It is sure possible to do better, but not useful for airliners. I think the Reynolds number for which the airfoil is optimized is the reason why even the U2 only reaches a glide number of 28.

 

[Linguofreak]

Yes, but also at least three times lower glide ratios as a high performance gliders. It is sure possible to do better, but not useful for airliners.

Of course. But I think it's more useful to say that gliders have *excellent* glide ratios than to say that airliners have poor glide ratios.

 

[Cairan]

Having given some thought and flown this accident a couple of times in X-Plane, I -think- I have an idea of what was different for this flight compared to other instances of water landings.

In this case, the wings were still loaded with fuel. This is different from a case of landing "light" due to fuel starvation of the engines after running on empty. Given the inertia of the fuel, and our thrusted formula F=ma, a larger mass in the wings would result in a slower deceleration. Taking into account that for a given speed, the force exerted to the wings and fuselage by the water, in Pascals, would be the same, there might be less of a difference between the deceleration of the main fuselage and the wings.

In other words, landing in the water with full wings (and maybe the center tank) kept them from being snapped away from the fuselage when they contacted the water.


Coupled with a descent to have the shallowest angle possible, this is probably what saved them in the end.

 

[Notebook]

Would the birds have commited suicide like that if they weren't Islamic terrorists?

I'm getting an image of a Canada goose in an explosive vest.

Coincidence, or are you moonlighting for a UK satirical magazine?

N.

 

[Andy44]

Having given some thought and flown this accident a couple of times in X-Plane, I -think- I have an idea of what was different for this flight compared to other instances of water landings.

In this case, the wings were still loaded with fuel. This is different from a case of landing "light" due to fuel starvation of the engines after running on empty. Given the inertia of the fuel, and our thrusted formula F=ma, a larger mass in the wings would result in a slower deceleration. Taking into account that for a given speed, the force exerted to the wings and fuselage by the water, in Pascals, would be the same, there might be less of a difference between the deceleration of the main fuselage and the wings.

In other words, landing in the water with full wings (and maybe the center tank) kept them from being snapped away from the fuselage when they contacted the water.


Coupled with a descent to have the shallowest angle possible, this is probably what saved them in the end.

That actually makes a lot of sense, good thinking. Full wing tanks give the wings a higher ballistic coefficient. And it helps that kerosene is lighter than water, so even loaded the plane still floats. I wonder if the accident analysis will say anything about this.

 

[Cairan]

With full wing tanks and a working APU, and remember, with fuel, even with engines out, the APU can still run and maybe even give flaps, slats, spoilers and other surfaces normally unavailable if fuel dry and with limited systems powered by a ram air turbine, the conditions were really different from any other ditching so far.

It's counter-intuitive that ditching heavy might be good, but in this case and if my theory is proven, it will probably change a lot of checklists regarding ditching. Instead of dumping fuel when in doubt of reaching a runway over sea, you might actually keep that fuel for buoyancy and structural reasons at impact.

 

[Moonwalker]

I think that most checklists are still optimized. Dumping fuel is not part of the A320 ditching and forced landing checklist anyway (but also Boeing ditching procedures usually do not include fuel dump). For immediate emergency landings above maximum landing weight, there is also an overwight landing checklist. The landing of US Airways flight 1549 actually was such an immediate emergency landing.

The A320 even has a "bomb on board" checklist