creating an area to move this discussion to a more accurate topic.

D.A.G.SEATTLE
Member
Member # 46
posted 13 November 2001 09:58 AM
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but the engines were made by G.E. maybe JMT can offer an opinion as to why they blew.
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D.A.G.SEATTLE
furdoo3@aol.com


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Posts: 771 | From: mukilteo wa. usa | IP: Logged

JMT
Member
Member # 474
posted 13 November 2001 11:29 PM
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Wendell, I think the plane was an Airbus A300-600. Those might be the only only A300-600s in the US, but they are not the only Airbus planes here. America West has a bunch of Airbus planes. Northwest has a boatload of Airbuses. US Airways does too. As does United. I don't think Delta does.
Most jumbo jets and most newer jetliners are offered with 3 major engine choices. The CF6 is made by GE, and thats what the AA jet had. Rolls Royce makes a RB211 engine that is in that same class. Pratt & Whitney also makes a competing engine. The airlines are free to choose which engines they want to use on the planes. Obviously initial cost is a major concern but it doesn't always go to the lowest bidder. Airlines also consider thrust ratings, time between overhauls, fuel consumption rates, tech support, parts availability, other engines in their fleet, noise, reliability, and other factors.

Just for the record, the engines are made to fall of the plane...under certain circumstances. The jet engine spins very fast and has almost no vibration. If you have ever played with a top, gyro, yo-yo, floor polisher or other gadget that spins a large mass, you learned a lot of physics lessons whether you knew it or not. Mainly, you learned that a large spinning mass is reluctant to move outside of it's axis. You also learned about gyroscopic precession. Anyway, the jet enigne mounts to the plane at a certain angle and is expected to stay on that axis. The mounting bolts are very strong in normal usage, but are designed to sheer or break off if it enounters extreme abnormal forces. So normally the bolts do a great job holding the engine to the plane.

What about abnormal forces? If you took a chunk out of that yo-yo or top, it would be so out of balance that it would be very difficult to spin, and would be very unstable, bouncing all over the place. The same for a jet engine. If it becomes unbalanced, it will start shaking real bad and leave that perfect axis.

It's probably a good guess that the AA jet engine lost it's axis. Why it did it remains to be seen. Here are some more common reasons. FOD, or foreign object damage. If the jet engine were to suck in something other than air, it might be enough to break off a fan blade and throw the engine out of balance. Engine have been known to suck in birds, debris on the runway, nose tire treads, nose gear doors, ice that built up on the engine inlet, blue ice that built up from a leaking toilet and they have been known to eat their own blades if one breaks off from stress or a bad mount. If it wasn't FOD, it could have had an internal failure that threw it out of balance. Another reason could be that the engine was forced outside of it's limits from a sudden airplane movement. Yet another reason could be a compressor stall. This happens when the engine can't suck in enough air and basically backfires. It can happen when the engine is at a high power setting, sucking in a lot of air, and suddenly the aircraft yaws (or skids) to a large degree. When this happens, the aircraft fuselage blocks the incoming ram air to the inlet. The engine can't suck in enough air so it burps. Sometimes these compressor stalls do no damage. Sometimes they do minor damage. Sometimes they start spitting out blades...and that is not a good thing.

Finally, as to why the engines are designed to break off, it is a safety thing. If the engine was hard mounted and welded to the wing, everything would be fine in normal operation. But IF the engine were to get out of balance, it would not only shake violently, it would be shaking the wing violently. And since the wing is mounted to the fuselage, the fuselage would shake violently. Throughout this shaking, there would be a weak spot somewhere and something would snap. The designers would rather let the fuselage and wings remain intact, and jettison the out of balance engine.

None of us know whay the AA jet went down. My first two theorys were...

A. Bird ingestion or other FOD. Sometimes, as the engines start to come apart, they spray fragments of the hot metal all over. These pieces can penetrate the fuselage, wing fuel tanks, and tail sections. Since both engines were recovered basically intact, it would be relatively easy to see if the first stage fan blades had signs of FOD. I believe the news said today that they ruled out bird strikes.

B. My second theory was airframe stress. In this theory, there was a sudden unforseen problem, and they needed to go back to JFK. In a rush to get back to the airport, the pilot turned the plane sharply to get headed back in the right direction to land. I figured that he overstressed the plane by turning too sharp and turning out of coordination. By coordination, I mean that the plane needs to bank and turn at the same time. Kinda like on a bicycle, you can't just turn the front wheel 90 degrees and do a hard left turn. Nor can you leave the wheel straight and just lean over to do a sharp turn. You gotta lean and turn. Anyway, this theory of mine suggests that when he did that, he could have broken the tail off. He could have stalled an engine. He could have done all sorts of fuselage damage.

There are still a dozen other likely theories. I'm gonna stick with my B theory for now. "Something" caused them to turn back, and they did it too quickly, exceeding the operating limits of the structure of the plane. At the moment he broke it, he went from pilot to passenger. It seems to best explain the tail section found in the water with no significant damage. It covers the engines coming loose intact. It covers the total loss of control.(nose dive) The flight data recorder will be a big help in proving this theory right or wrong.

It could have been A and B.

It is a sad situation, and I am not trying to convince you of one theory or another. Nor do I know why the jet went down. The media is throwing you a lot of tidbits, and I think you would be better off knowing how to digest them.


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Posts: 168 | From: Grapevine, TX , USA | IP: Logged

D.A.G.SEATTLE
Member
Member # 46
posted 14 November 2001 12:58 AM
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Thanks JMT--your b theory makes sense to me.i couldn't figure out how both engines and the tail "fell off"the plane.
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D.A.G.SEATTLE
furdoo3@aol.com


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Posts: 771 | From: mukilteo wa. usa | IP: Logged

Lee-PA
Member
Member # 476
posted 14 November 2001 04:36 AM
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JMT,
Thanks for the explanation.
How about an accedental engine reversal? Wouldn't that sort of twist the plane to allow all the parts to break off also? I seem to remember (can't recall when or where) this theory has happened before.
On another note, TWA has a bunch of AirBusses also, and I expect they'll all be repainted soon with AA colors.

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Lee-PA
lee@talkvegas.com


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Posts: 516 | From: PA | IP: Logged

JMT
Member
Member # 474
posted 14 November 2001 06:07 AM
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You're right Lee, an accidental reversal could easily do it. I was looking for that on the engine that landed at the gas station. That enigne did not appear to go into reverse. You know what a jumbo jet engine looks like in reverse. It looks like about a 1 foot gap going around the engine. Another symptom might be that the visable section behind that gap being ripped off by forward thrust deployment.
Airlines take reversal systems very serious. It was a Lauda Air Boeing 767 owned by race car driver Niki Lauda that made a lot of headlines when it went into reverse in cruise flight and crashed.

Two of the biggest media popularized engine departures happened to American Airlines. One was many years ago when a Boeing 727 going to California lost a #3 enigne due to blue ice from the forward toilet. The crew saw all of it's cockpit indicators for that enigne go to zero and "assumed" it just flamed out. It wasn't until the plane landed that they found the enigne missing. The other popularized case was the DC10 in Chicago where the engine came off, taking a lot of the wing and wing control systems with it.

And it's not just AA. All the airlines have had some enigne problems. The United jet in Souix City Iowa and a Delta jet in Florida had engines explode doing a lot of damage. Most 737 operators have had the rear engine mount "sheer off". Usually the result is that the rear of the engine hangs down about a foot. Sometimes the entire engine completely leaves the plane.

One more note. Most of the engine makers only make forward thrust engines. The airfame manufacturer, such as Boeing or Airbus will contract a thrid party to design a reverser system for that plane. That is because a given engine can be mounted a number of different ways on different airplanes. And some jet engines are used in industrial operations and are forward thrust only. Some forward thrust applications include enignes used in power plants, pipe line pumps, train engines, or boats.

Since the Lauda Air crash, the indications and control system black boxes for the reversers have become much more complex. It may have been a reverse situation or even a reverser warning light that caused the AA flight crew to want to go back to JFK.


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Posts: 168 | From: Grapevine, TX , USA | IP: Logged

Thanks JMT - your explanations make more sense than some of the experts I have heard on TV. Talk to us about the "other Air Buses" in service with other airlines. Made overseas or in U.S. For some reason. I have more confidence in our abilities than other countries. Also, would be interested in your opinion of the 737 and MD-80. Maxine was on a flight where one engine went out (did not fall off) and said the flight and landing was "smooth" - was not sure what type of aircraft she was in. Hope all of this does not scare Lee's family from their trip to LV. Wendell

JMT--in regard to the tail section--did it whiplash off the plane?

Wendell, I'm with you. I have a lot more confidence in American quality in terms of aviation. That extends to American engineering, American research, American testing, American standards, American assembly, etc. I've worked on a lot of foreign airplanes including the Embraer aircraft that killed Texan John Tower, which BTW was engine problems. That airplane was built under Brazilian technology. I like their coffee better than their planes.

Airbus planes are built in France. But they are French technology. It is a consortium of at least 5 different countries that build various pieces and ship them to France for assembly. So it is different technology, different research, different quality control, etc. My biggest complaint with working on the Airbus A320 is communication. For instance, one small system on the plane may be made by the Germans. It's probably a very good system. The Germans send their instructions, supporting data, service manuals and other papaerwork to France. Well, the French translate all that paperwork into French for their people to utilize. Then we buy the plane in America, and they translate all that info into English. If you have ever studied foreign languages, you know some words just don't translate very well. It is my own personal opinion that while it is amazing that so many language barriers have been overcome, there was still some vauge and questionable wording in my English training and the English manuals.

Most of the Airbus planes in the US are A320 jets. They are being replaced by the A319. Also, at DFW, sometime around 1:30, you can see a four engine Airbus with Lufthansa colors landing.

Some of the planes I work on have the General Electric CFM56 engine. It was originally built by a consortium also. I have not run into the language barrier that I found in the Airbus plane. This summer I went to a GE engine facility in Ohio and found the training top notch. Nothing like what I had at Airbus.

Working on Airbusses, MD-80s, and 737s is kinda like a Ford, Chevy, Dodge deal. The Airbusses have a slightly larger fuselage, the MD-80s have rear mounted engines for better quietness in the cabin, and the 737 follows the research and development of it's Boeing family. It has many proven systems that were used on the 707 and 727. On the downside, I really don't like Airbusses period. MD-80s, like all McDonald Douglas planes are not mechanically friendly. The 737s are more noisy because the engines are on the wings.

DAG, that is just a theory that it got whiplashed off. Judging by the vibration that is being reported today, the tail may have been loose. But I think I will stand with Theory B for a little while longer. I haven't studied the news to see what turns the plane made. The Digital Flight Data Recorder will tell us a lot. It records stress off of accellerometers mounted on the plane, as well as control inputs from the cockpit.

Thanks JMT - I can certainly see where info such as the above can be quite benefical to those of us on this BB who like to fly in and out of LV. Why don't you join us Tuesday?? Wendell

I guess we all tick differntly. For some strange reason the fact that it wasn't (or atleast doesn't look like terrorist) seems to calm the flying public down. To me the factthat it just fell apart for no aparent reason spooks me more!

I'm guessing we won't really know what happen for a long time. Those NTSB things seem to drag on and on. Still with no hard conclusive reason.

JMT, Those Embraer's scare the heck out of me as far as small planes go. But what is the name of those "flying box cars" I don't even know if you know what I'm talking about, but that is what we always called them. they where comuter planes, high wing, sat maybe 20-28 people? UsAir flew alot of them in our area. Just wondering who made them really. They looked like an odd duck to me.
Also again thanks for the information and sharing your ideas and views.

Lee, those boxcars are made by Shorts. It's an aircraft and missle company based in Belfast Northern Ireland. I worked on them a few years when I lived in Louisiana. We had about 10 of them. The scariest part of them was that the fuel tanks were mounted in the ceiling. So if the plane had a fuel leak you could see fuel dripping down through the passenger windows. It had a lot of other wierd factors too. In general it was better than the Embraers.

On AA 587, I caught the end of a blip that showed the vertical tail attachment points where they were broken. It wont take much work by the investigators to find out if they were previously cracked, previously stressed, corroded, or snapped off on the last flight. It's a real possibility that they were stress cracked and or corroded for a long time, and the finally gave way. I'm not buying the wake turbulence from the 747 ahead of it.

Sorry Wendell, no trips to LV this year. I hope y'all have a blast!

Joe, I have 2 questions. I heard that the airplane was 13 years old. Is that considered "old" for an airplane?
And, how often do planes undergo a complete maintenace inspection?

It's just mind boggleing to be flying along and have the tail fall off your plane!!! the plane did have a violent shaking incedent in it's flying history

That's not old by airline standards. It takes about 10 years to go through a complete maintenance cycle. They are done in phases, called A checks, B Checks, C checks, and D checks. And each of those phases is broken down into phases so that when all phases are complete, that entire inspection is done. Here is an hypothetical example.

A1 check every 7 days
A2 check every 14 days
A1 & A2 together every 21 days
B1 check every 30 days
B2 check every 60 days
B3 check every 90 days
B4 check every 120 days
C1 check every 120 days
C2 check every 240 days
C3 check every 360 days
C4 check every 480 days
1/4 D check every 750 days
1/2 D check every 1500 days
Full D check every 4000 days

Whenever a B check is done, both A checks are done too.
When a C check is done, whichever B check is next on the list is done along with both A checks.
When any D check is done, All A, B, and C checks are done too.
Under a program like this, whenever a plane comes out of maintenance, it is reset to zero time regarding lesser checks.

An A check is mainly a good visual check along with checking fluids, pressures, lights, emergency equipment, and stuff that's easy to get to.

A B check involves filters, lubrication and full detailed checkouts of systems and electronics. It can be done overnight on the ramp or in a hangar.

A C check involves opening inspection panels, removing a landing gear, removing engine fan blades, and checking the rigging of flaps, landing gear, doors, flight controls, etc. This takes every bit of an overnight to do, requires special inspection and calibrationn equipment, and is done in the hangar.

The D checks involve removing anything that is removeable, including seats, galleys, floorboards, black boxes, windows, wing panels, flight controls, engines, and stripping the airplane down to a skeleton and skin. A structual inspection is performed checking for corrosion, wear, and cracks using very specialized equipment. The airplane is often shored up in jigs because the airplane cannot suppor itself with so many structural components removed. All removed components undergo overhaul before they get put back on. The D checks take about 3 weeks to 2 months to complete. When the plane comes out of a full D check, it "should be" a brand new airplane in regards to maintenance status.

In regards to feeling safe on a plane, I'd much rather fly in a 11 year old airplane recently out of a full D check than fly on a 4 year old airplane.

In addition to the phase checks, certain parts have a hard time when they must be changed by, regardless what check is due. The airlines usually try to schedule these replacements during a check if possible. Thes compnents include engines, landing gear assemblies, flap drive motors and gearboxes, some radio and navigational boxes, and most of the emergency equipment.

DAG, that could easily be it. It could be the previous vibration cracked something, the wake turbulence aggrivated it, and the evasive manuever snapped it. Or maybe it got previously cracked on the previous accident and it finally gave way.

I'm pretty sure the crew never knew the tail fell off. I'm guessing all they knew is that they were experiencing symptoms they could not quite understand completely, further complicated by their corrective actions not responding to their inputs. For instance, they may train for wind shear time and time again, but never actually experience it. They know what it feels like in the simulator and they understand that not all windshear situations are the same. They train for heavy wake turbulence from other aircraft, but they never actually encounter it and they know that not all wake turbluence is the same.

They MIGHT have mis-diagnosed a loose tail for wake turbulence. In that situation, they are trained to add power and fly out of it. In the Monday morning quarterback seat, IF the vibration was actually loose tail feathers, the corrective action might be to back off on the power, slow the plane down, use asymetrical engine thrust to turn the plane instead of the rudder, and make very wide shallow turns to get the plane back on the ground.

A friend at work told me that the Airbus tail section that fell off the plane was made in Spain.