AA Flight 587

[3WE]

A few comments- a compressor stall sort of basically means it stops sucking air. Whether you suck air or don't, there isn't NECCESARILY any physical evidence of it (although Don mentions the blades being bent back).

I think one can say that 727 engine #2 stalled "somewhat regularly" without any sort of physical evidence or follow up needed.

Now along these lines: (This may be a stupid comment), but who says a compressor stall has to go "bang".

I do recall one on a 727 and it certainly did go BANG, but I also recall L-1011 RR start ups where there would be flames behind the engine, but no bang. A start up isn't a compressor stall, but I THINK the bang is sudden ignition of fuel-air mixtures...so even if the plane spewed some fuel-air into a 200 MPH slip stream, maybe it burned instead of exploded.

As to "no evidence of pre impact damage", I thought this aircraft DID break up (including engine separation) before ground impact- but at a time when speed and attitude would have built up & combined into forces generally expected to cause breakup.

[Dmmoore]

A few comments- a compressor stall sort of basically means it stops sucking air. Whether you suck air or don't, there isn't NECCESARILY any physical evidence of it (although Don mentions the blades being bent back).

Actually they bend forward.

I think one can say that 727 engine #2 stalled "somewhat regularly" without any sort of physical evidence or follow up needed.

Apples and oranges. Okay, P&W and G.E. They behave very differently in a stall. The Pratt is designed to accept an occasional stall as part of it's "NORMAL" operating experience without damage. The General builds engines to operate without stalling and thus when they do, the compressor blades can be damaged.

Now along these lines: (This may be a stupid comment), but who says a compressor stall has to go "bang".

While a quite stall may occasionally happen, a stall caused by blocking the inlet will almost always be an explosive event.

[quote]I do recall one on a 727 and it certainly did go BANG, but I also recall L-1011 RR start ups where there would be flames behind the engine, but no bang. A start up isn't a compressor stall, but I THINK the bang is sudden ignition of fuel-air mixtures...so even if the plane spewed some fuel-air into a 200 MPH slip stream, maybe it burned instead of exploded.[/quote

The flames you observed from the tail pipe at start up were not caused by a stalled condition. Over rich or not fully propagated flames in the burner section can cause the tail pipe flames.

As to "no evidence of pre impact damage", I thought this aircraft DID break up (including engine separation) before ground impact- but at a time when speed and attitude would have built up & combined into forces generally expected to cause breakup.

The noises heard and the fire seen may have been the sound of parts failing and engine separation. Fuel line breakage and associated ignition of the fuel could make a nice fire.

[scottkin]

In the link I'm providing below, check out the last few frames on the video from the toll booth. Im curious as to what was on fire as it dropped from the aircraft. Im assuming its the engine but im not sure. You can see the airplane in the video still above the flaming debris. Any thoughts on this? http://www.ntsb.gov/events/2001/AA58...d_mtg_anim.htm

[cegro27]

Reports were that one or both engines separated from the a/c before it crashed, so that [the engine(s)] would be the flaming debris you see in the video.

[Schorsch]

Just one remark as I am professionally connected to aircraft tails: it is the Vertical Tail Plane (VTP) and not the rudder. Big difference. If just the rudder had fallen off, no bang, no scrap, no bloodshed. But it was the whole VTP with the VTP attachments failing.

[FireLight]

Just one remark as I am professionally connected to aircraft tails: it is the Vertical Tail Plane (VTP) and not the rudder. Big difference. If just the rudder had fallen off, no bang, no scrap, no bloodshed. But it was the whole VTP with the VTP attachments failing.

If the rudder goes but the VTP remains, how would they turn? Do hydraulics remain intact if only the rudder goes? Or do they use differential thrust to get the bird back home?

[cegro27]

The rudder is only used to keep the nose centered with the aircraft's flight path during turns, or keeping the nose steady while flying in strong winds. The plane could make a turn without the rudder, it would just be an uncoordinated (sloppy) turn. The rest of the vertical tailplane, the vertical stabilizer, "is" needed to maintain the plane's directional stability. Without it (rudder included) the nose would have no stability at all and a crash would result.

As for the hydraulics, it would depend on whether any hydraulic lines were cut by the loss of the rudder, and what specific hydraulic systems were affected. Differential thrust could be used (assuming the engines were still attached) if the plane suffered a serious hydraulic failure that affected the use of the ailerons as well.

[Dmmoore]

Correct. The vertical stabilizer provides directional stability critical to aircraft flight. Remember the DHL A310 that took a hit from a missile and landed safely (though not without additional damage) without hydraulics, and most of the R/H outboard flap using only differential thrust. A masterful job of airmanship.

[Airbus_A320]

If the rudder goes but the VTP remains, how would they turn? Do hydraulics remain intact if only the rudder goes? Or do they use differential thrust to get the bird back home?

As stated before the ailerons can be used to turn the plane, it would just be uncoordinated, but they could get it back safely. A while back an Air Transat A310 out of Cuba lost the entire rudder and was able to return safely.



Not sure how good/accurate the two articles are, but they should give a basic idea of what happened.

http://www.iasa.com.au/folders/Safet...rudder-sep.htm

http://technology.newscientist.com/c...ous-flaws.html

[Leftseat86]

Correct. The vertical stabilizer provides directional stability critical to aircraft flight. Remember the DHL A310 that took a hit from a missile and landed safely (though not without additional damage) without hydraulics, and most of the R/H outboard flap using only differential thrust. A masterful job of airmanship.

IMO even more amazing is how long JA123 stayed in the air.

[Gabriel]

IMO even more amazing is how long JA123 stayed in the air.

Flying more or less with the same stability that a leaf in the wind (permanent oscilatons of very large yaw and bank angles in ecxess of 90 degrees).

[Dmmoore]

IMO even more amazing is how long JA123 stayed in the air.

It would have been quite a feet if they could have figured out how to keep its oscillations under some control. The out come may have been much better.

In truth, the length of the 747's fuselage vs the frontal area is much better than the Airbus. The 747 tends to be more stable with the vertical fin missing.

[FireLight]

It would have been quite a feet if they could have figured out how to keep its oscillations under some control. The out come may have been much better.

In truth, the length of the 747's fuselage vs the frontal area is much better than the Airbus. The 747 tends to be more stable with the vertical fin missing.

I hope you mean " ... more stable than the Airbus with the vertical fin missing." Otherwise, they've been wasting a lot of time, money and energy putting VF's on 747's.

[Gabriel]

It would have been quite a feet if they could have figured out how to keep its oscillations under some control. The out come may have been much better.

In truth, the length of the 747's fuselage vs the frontal area is much better than the Airbus. The 747 tends to be more stable with the vertical fin missing.

The sweep of the wings also adds directional stability, and the wings of the 747 are more swept than most (inlcuding all airbus).

Yet, not enough to make it usefully stable without a fin.

[Schorsch]

Flying without rudder is generally not a problem. Of course, it would be very fugly feeling, especially as Mr. Yaw Damper cannot do his magic. But it would work.
The other problem mentioned is hydraulics. The pictured A310 apparently kept his fluids. Otherwise he would have been in trouble.

The DHL A300 that was hit over Bagdad was lucky in two ways:
First, they flew a virtually empty aircraft. With full load the things would have become much more difficult.
Second, the crew did train that sort of thing a bit. A normal crew would have failed.

The Japan Airlines aircraft did have some fin area remaining.
Without VTP no conventional current FAR25 passenger aircraft is controllable, at least not under standard conditions. I read an AIAA paper applying this problem theoretically. It concluded that the aircraft can be controlled in total absence of a VTP, but it needs some sort of dedicated (automatic) controller. Theoretically something you could put into the EFCS, while the current approach of decoupling the pilots pedals from the actual rudder makes sense, too. For the A320 and earlier A330/340 this was the only control that was really controlled directly, now you control sideslip angle via pedal.

The sweep of the wings also adds directional stability, and the wings of the 747 are more swept than most (inlcuding all airbus).

The B747 has 37.5°.
The A380 only gets 36° in one section.
Rest of the Airbus fleet is lame and slow.