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Posted: 11/13/2001 9:27:03 PM EDT
[#1]
As you have suggested both engines dont fall off an airliner.. even one doesnt happen but once every 10 years or so. With 5,000 flights each day in the u.s. The math is simple.
But on the other hand how many G.E. CF6 engines have blow up and caused a crash? Four in the last 3 years... I think the left engine did a KB and initiated a total break up of the aircraft. I am a Mech for an airline that has had a CF6 KB so I have a Basis for my theory. I may be VERY WRONG but it is my gut feeling...pat |
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Posted: 11/13/2001 9:41:12 PM EDT
[#2]
If you want to see what a cf6 will do to an aircraft when it KB's see topic 69213 page 2....pat
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Posted: 11/13/2001 9:44:35 PM EDT
[#3]
"...how many GE CF6 engines have blown up and caused a crash?"
You know, I found a statistic a couple years ago that stated the CF6 series has a 99.96% dispatch rate...that basically represented a expected failure every 12 years if I remember the numbers right. - Anarki |
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Posted: 11/13/2001 9:49:51 PM EDT
[#4]
Remember the Suix City crash? that was a cf6. ever hear of the continetial engine that caused the trash on the runway leading to the sst crash? see the pics of usair N654us with engine scattered all over the place...
Go to the FAA web site and search the history of the CF6. The law says that when an engine does a total KB the parts must be contained... The CF6 cant do it...pat |
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Posted: 11/13/2001 10:05:05 PM EDT
[#5]
If you really want to get into the technical details on why the CF6 hi p turbine wheels come apart....
It is not the basic design or normal wear and tear. It is in how it is overhauled. The individual blades have to be removed from the disk before it is inspected. The engine shops, even the ones owned by G.E. use a small steel rod to drift the blades out. This causes very small cracks on the disk at the blade root. During inspection the cracks are noted and blended. Often not deep enough. When you have a piece of titanium spinning at about 10,000 rpm heated to over 600 degrees c. supporting about 100 blades and it has a very tiny crack it will fail. This has been documented by the FAA, the USAF and the NTSB. Every inspector, in every engine shop, in the world has been made aware of the problem in the CF6, but still it happens.... Go to the faa web site then to ad's once there do a search using cf6 as a key word. You will be amazed at the problems with this engine...pat |
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Posted: 11/13/2001 10:29:39 PM EDT
[#6]
PaterPat, that was a different CF series engine on the United DC-10. It was a CF6-50 series engine and number #2 was found to have a worn out turbine disk. The CF-6 80 series engines I have work on are highly realiable. Too have both engines to drop off an airport is astronamical. I would not take anything from reporters or so-called experts about the engines untill a complete inspection report on the crash is released. FYI, a lot of the KC135s and KC10s are using CF6-50 series engines. I had no idea why I was think about the SCENMA CF5 engines.
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Posted: 11/13/2001 10:34:11 PM EDT
[#7]
I work on the cf6 daily as a line mech for usair working international gates in pit. We watch this engine very carefully. Go to the faa web site and look under ad's then search the cf6. you will find the data that i am talking about.
The engine is not bad its just how it is overhauled...pat |
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Posted: 11/13/2001 10:55:38 PM EDT
[#8]
[b]How often do both engines fall off a jet?[/b]
once? |
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Posted: 11/13/2001 10:57:01 PM EDT
[#9]
ARChoo wins!
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Posted: 11/13/2001 11:23:28 PM EDT
[#10]
WooHoo! What do I get? 2002 LEGP?
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Posted: 11/14/2001 2:48:53 AM EDT
[#11]
NTSB has reported that No Bird Strike or catastrophic engine failure (meaning they were mostly intact). The rear stabilizer was one of the first things off the plane. The terrorist act is starting to receive more play in the media. With most eyewitness accounts seeing some fire or explosion in the air prior to the engines falling it is probably the most likely scenario now.
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Posted: 11/14/2001 3:22:48 AM EDT
[#12]
Vertical stabilizer falling off is even more unlikely than two engines doing so. After that happened, I wonder if the instabliity then caused the engines to depart? IMHO the key is how the stab came to leave.
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Posted: 11/14/2001 5:28:42 AM EDT
[#13]
The law says that when an engine does a total KB the parts must be contained... The CF6 cant do it...pat I could be wrong on civilian aircraft, but I am almost positive that you are only required to contain a blade if thrown. It would almost impossible to contain a ruptured disk if it came undone, especially an HP turbine disk. Those have so much mass and energy, combined with the fact that they are made from some of the hardest(and strongest) metals on the planet mean they would be VERY difficult to contain. I have only had experience with military engines, but the design criteria for most of those was that you had to contain any single blade if lost. Worst cases being a first stage fan blade, or an HP turbine blade usually. As far as the vertical stabilizer falling off, I think that is key, it was awefully clean cut to have happened by being torn off or blown off. A friend wife believes it was a terrorist act of sabotage, and the gov't is trying to keep it quiet to keep from destroying the Airline industry. Possible? What are your thoughs. |
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Posted: 11/14/2001 5:38:18 AM EDT
[#14]
It is not my understanding that the NTSB believes that the engines "just fell off." Recent scenarios point to the tail fin tearing off. The resulting instability and torsion of the aircraft caused the engines to rip off.
At least that is what they're reporting now. I believe it was an accident, plain and simple. A very bad timed accident, but an accident just as well. |
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Posted: 11/14/2001 10:00:28 AM EDT
[#15]
Aren't pylon mounted engines designed to fail and come off under extreme conditions ( high-G , side load etc. ) to prevent further damage to the aircraft ? If you watch the wreckage footage they show the tail end minus the vertical stab and horizontal stabs.
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Posted: 11/14/2001 10:13:46 AM EDT
[#16]
Quoted: Aren't pylon mounted engines designed to fail and come off under extreme conditions ( high-G , side load etc. ) to prevent further damage to the aircraft ? If you watch the wreckage footage they show the tail end minus the vertical stab and horizontal stabs. The plane never reached speeds high enough to generate the G loading required to shear the engines, and was reportedly barely able to remain airborne due to low airspeed. Per aviation talking head on Fox News this AM, the above. The shear at the vert. stabilizer was too clean, unless all of the brackets failed at once. This still does not explain both engines shearing, nor the breakup of the airframe while in the air. Again, the plane's airspeed was reportedly too low to generate enough g-force to break up in flight. If you aiplane people could satisfactorily explain the astronomical number of coincidental failures on a plane with major service maint/inspection less than 2 years ago, I would feel more inclined to believe the official line (that came out less than 30 minutes after the crash, while emergency personnel were still arriving, and before the gov't alphabet soup reps arrived). Don Out |
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Posted: 11/14/2001 10:24:22 AM EDT
[#17]
The tail thing wasn't even struck by anything. Obviously I don't know a lot about planes (tail thing), but I do know for that a big piece of metal like that shouldn't just fall off.
My guess is sabotage. -SS |
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Posted: 11/14/2001 10:41:09 AM EDT
[#18]
Its starting to sound like there was a wake effect going on. The JAL 747 flight ahead of it was 20 sec late, not allowing for the proper interval. That might explain the loss of the vertical stabilizer. But these planes are built to take such stresses. There are documented cases of 737s and 727s going down after following too close. The vortexes created are supposedly extremely strong.
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Posted: 11/14/2001 10:47:39 AM EDT
[#19]
I was watching a history channel program a few nights ago called Broken Arrow. It was about some of the nuclear disasters in the 1950's where we lost a few nukes and spread radiation all over the place. In a few of the B-52 crashes, the huge rear vertical stabilizer was to blame. Just like that nearly perfect tail section they hauled up out of the water the other day, when the B-52 stabilizer sheered off, the plane instantly nose dived due in part to the instant loss of mass/wieght and stability. In the B-52, many times the entire rear end fell off soon after as it lurched forward.
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Posted: 11/14/2001 11:40:30 AM EDT
[#20]
Federal investigators said yesterday the co-pilot of doomed American Airlines Flight 587 called for "max power" four seconds after the frame of his A300 Airbus was rattled twice, possibly by the wake of a larger plane.
Nineteen seconds later, both engines and the tail inexplicably began tearing free of the plane, which had just taken off for Santo Domingo, Dominican Republic, from John F. Kennedy International Airport. The pieces and the rest of the aircraft began falling in a straight line down into the ground. All 260 persons aboard were killed, as apparently were five persons missing from homes that the plane hit. National Transportation Safety Board officials all but ruled out bird strikes or spontaneous disintegration of engine parts as causes of Monday's crash during a dramatic news conference where NTSB Chairman Marion C. Blakey said the probe was "coming to a head." |
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Posted: 11/14/2001 12:10:25 PM EDT
[#21]
After I saw the video of the NTSB & FAA fly a 737 directly behind and clearly in the vortex of a 747, vortex break up doesn't sound plausible to me. Otherwise, problems with the airframe would have been easily discovered in the last inspection.
The other fact that nobody seems to talk about (or I've not heard) is that this plane bounces back and forth to the Dominican Republic who's airport security may be a concern as it is not the US. |
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Posted: 11/14/2001 12:36:57 PM EDT
[#22]
My money is still on the possibility that the thrust reversers somehow became activated shortly after takeoff. That would explain the low airspeed and the engines ripping off the plane.
It happened in 1991 with a Laudia Air 767, killing 127 people when it crashed in Thailand. Of course, that was a Pratt and Whitney PW4000 engine, not a GE CF6. God Bless Texas |
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Posted: 11/14/2001 12:58:09 PM EDT
[#23]
Quoted: My money is still on the possibility that the thrust reversers somehow became activated shortly after takeoff. That would explain the low airspeed and the engines ripping off the plane. It happened in 1991 with a Laudia Air 767, killing 127 people when it crashed in Thailand. Of course, that was a Pratt and Whitney PW4000 engine, not a GE CF6. God Bless Texas How would the thrust reversers rip the engines of the plane? I can definately see how it would crash since it would not have any airspeed. |
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Posted: 11/14/2001 1:28:17 PM EDT
[#24]
I have been hearing here and on the news that the plane might have been going to slow. It had already been airborne for 3-4 minutes. For those in the know what is the acceleration rate of the aircraft?
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Posted: 11/15/2001 10:04:33 PM EDT
[#25]
Keep in mind that MAINTENANCE practices can cause serious damage to any airplane.
The extremely infamous American Airlines DC-10 crash back in 1979, which essentially destroyed Douglas Aircraft and its DC-10, happened because some maintenance morons at American figured they'd save some time by pulling engines off for maintenance in a faster -- but completely unsafe and irresponsible -- way. They cracked the pylon that the engine hung from but didn't notice when they reassembled everything. Then that engine fell off during takeoff, the pilots apparently misinterpreted what was happening, and the rest is history. In other words, to answer the initial question of "how often do both engines fall off a jet?", the answer is "it depends on whether the jet was maintained properly." Given American's complete failure to follow manufacturer's recommended practices in 1979, I really wouldn't be surprised to find that they'd done something similar again. |
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Posted: 11/16/2001 5:13:59 AM EDT
[#26]
Long term performance of composite structures is an area of evolving knowledge. As an example, aluminum helicopter blades have a finite service life, in hours. At end of life they are supposed to be scrapped. Composite blades are supposed to NOT be life limited but rather renain in use as long as they pass inspection. Some aircraft can use either (as a set, of course). Seems the metal ones, in fact, have the longer life!
Composites are light and strong. They are difficult to properly repair. VERY difficult to properly inspect. Long term integrity is somewhat of an unknown. The fin of the A300 is composite. This one was possibly exposed to high stresses in 1994. It was repaired near area of failure. How the heck was it inspected following these events? Many unanswered questions! Sadly, the government is known to be a bunch of liars so a question is always likely to remain! |
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Posted: 11/16/2001 5:43:18 AM EDT
[#27]
My theory/unedumacated guess:
Plane takes off- flies through vortex(s) bad rear tail fin falls off- no side to side control (or plane slips sideways too far before pilots can correct) plane goes sideways through air, engines shear off due to sideways pressure instead of push/pulling (front/rear). rest of plane starts to break up due to incorrect sideways forces on body. crash planes-like missles/space shuttle etc will go fine straight through air at hish speeds, but if tilted slightly, it puts massive strain on it- if it goes too far, it will tear it apart. Kinda think of it as when you carry that plywood on the top of your yugo and you hold it up there by hand-it will be fine if held straight through the air, but if it is tilted, and wind gets under it, say goodbye to the plywood. (don't do this-get a pickup) Or something.... |
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Posted: 11/16/2001 11:22:50 AM EDT
[#28]
Quoted: I have been hearing here and on the news that the plane might have been going to slow. It had already been airborne for 3-4 minutes. For those in the know what is the acceleration rate of the aircraft? It'll do 0 to 170 in a half mile - aka takeoff. |
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Posted: 11/16/2001 11:49:30 AM EDT
[#29]
HAMBONE: After the airplane has been cleaned up(gear and flaps up)the pilots accelerate to 250 knots indicated airspeed(KIAS). 250 is the max speed that a jetliner can go below 10,000 feet in the US. I would think that the Airbus was at or approaching 250 when the problem occurred. I have been flying jets for over 30yrs and I have never, ever heard of a vertical stabilizer separating from an airplane.
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Posted: 11/16/2001 12:07:52 PM EDT
[#30]
I originally posted that i thought the left eng came apart causing the aircraft to come apart. I now looks like I was way wrong.
As for tails coming off Allegany had one in a bac111 but i think this was caused by a fire in the tail compartment. I also think the Virgin aircraft that broke up in flight lost its tail when the thrust reverser deployed in flight. |
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Posted: 11/16/2001 1:34:46 PM EDT
[#31]
Quoted: My theory/unedumacated guess: Plane takes off- flies through vortex(s) bad rear tail fin falls off- no side to side control (or plane slips sideways too far before pilots can correct) plane goes sideways through air, engines shear off due to sideways pressure instead of push/pulling (front/rear). rest of plane starts to break up due to incorrect sideways forces on body. crash planes-like missles/space shuttle etc will go fine straight through air at hish speeds, but if tilted slightly, it puts massive strain on it- if it goes too far, it will tear it apart. Kinda think of it as when you carry that plywood on the top of your yugo and you hold it up there by hand-it will be fine if held straight through the air, but if it is tilted, and wind gets under it, say goodbye to the plywood. (don't do this-get a pickup) Or something.... I think Cletus is on the right track. Think asyemetric. The wake was likely a factor but only a contributing. Thrust reversers were mentioned as was the horizontal stabilizer. Wake turbulence should not cause a horizontal Stab to come off, or a a thrust reverser to deploy, but if it did, it could quickly turn the plane off axis in relation to the relative wind, causing overstess that causes parts to fail. |
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Posted: 11/16/2001 3:16:48 PM EDT
[#32]
Here's a series of pics of a 747 vortex in action (scroll down a few pics)...
[url]http://www.aviationpics.de/pretty/pretty.htm[/url] |
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Posted: 11/16/2001 3:19:24 PM EDT
[#33]
It appears to be once a year....so far...
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Posted: 11/16/2001 5:19:26 PM EDT
[#34]
They were saying on MSNBC that all the fasteners for the tail fin were still attached to the fusilage. And that according to aircraft maintanance records, this individual jet had had a trip back to the factory to deal with delamination around the fin/fuselage joint. It is a all carbon fiber tail.
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Posted: 11/17/2001 12:01:58 PM EDT
[#35]
Quoted: Here's a series of pics of a 747 vortex in action (scroll down a few pics)... [url]http://www.aviationpics.de/pretty/pretty.htm[/url] Lovely pictures -- I especially like the farting SR-71. But I *really* don't think the wake turbulence was the problem. Oh, it might have triggered things, but all of the news reports so far indicate that there was plenty of time for the vortex to dissipate to a safe level, even if the reporters are whining hysterically about how that must be the cause. Sorta like, yeah, the noise might trigger the avalanche, but the huge mass of snow-on-a-slope was a danger even without the noise. . . . |
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