Posted on 11/16/2001 1:16:03 PM PST by Agent Smith
Up until now, my best guess as to the cause of the 587 crash was defective/substandard bolts used in attaching the vertical stabilizer to the tail and a failure to detect the problem through inspections.
However, I heard on the news last night that the vertical stabilizer was not fabricated from aluminium, but from a carbon fiber composite. This material is very strong and light but can fail catastrophically if a stress fracture/crack develops. Based on the photos of the recovered stabilizer showing that it was cleanly severed from the tail, I now believe that this is the most likely cause of the accident.
The turbulence from the JAL 747 was the straw that broke the camel's back.
I'm not so sure about this statement. An American Airline pilot friend of mine says that security is extremely lax on the ground, in areas where the public is not allowed. He has always been nervous about baggage handlers, mechanics, etc. due to the fact that they seem to be able to go wherevere they please, unrestricted.
Would someone explain to me the physics behind wake turbulence? I can't understand how there could still be turbulence and jet wash from a plane that has left that immediate airspace 45 seconds ago -- even with no wind.
Meanwhile, in Tulsa, the maintenance records group discovered that one of the six main attachments that held the Flight 587 plane's tail to the fuselage underwent a significant repair in 1988, soon after the plane rolled off the assembly line but before it was delivered to American.So the last inspection of the 13 year-old repair was 2 years ago. How much experience is there with assessing incipient failures with this kind of repair? How did they pick a five year inspection interval?The left-center fitting "delaminated," and technicians in Toulouse, France, where the plane was built, added a "doubler" and rivets to reinforce the joint, Black said at the evening briefing. Airbus then delivered the plane to American but did not indicate that special inspections of the repaired area were necessary.
The attachments are to be checked every five years, Black said. The last check of the American A300-600's tail/fuselage attachment fittings took place in December, 1999, which is also when the plane had its last heavy maintenance visit.
"However, that also should have produced a prominent heading change, as a first event."
Absolutley-- matching the FDR data to the radar tracks will be crucial to making this theory plausible. If the aircaft were suddenly pitched/yawed/rolled, whatever, absent input from the flight deck, then we can legitimatley yell 'wake turbulence'. It is telling that the crew did just that-- they ID'd the behavior of the aircraft as wake turbulence.
Supposing we are right, the issues (to me) remain -- why did the VS fail, and why are A300s not grounded right now if they cannot, even in one instance, survive CAT/WT?
To American's credit, I believe THEY have grounded all A300s subject to sucessful inspection of the VS assembly.
Best bet is you are wrong, as an A&P mechanic, I HAVE seen delamination, and I KNOW what it takes to delaminate carbon fiber. It isn't easy. Also, in the area under discussion, it is almost impossible to discover delamination withought removing all of the access covers. This is normally done at a 'D' check which occours on a hours/cycles (landings) basis. If there has never been a problem with that area before it doesn't need to be specially checked again. After this incident, I am positive the area will be checked just like when all of the DC-9/ MD-80 series aircraft jackscrews were checked after the Alaska Airlines incident in California. Lets keep our heads on here people.
Yes, I concede the NTSB and FAA are torn between the airlines and safety but, let them do their job and keep your uninformed opinions to yourself.
A big heavy airplane, like a 747, moving through the air, has to produce a lot of thrust and lift to fly, so it has to move a lot of air from where it was to where it need to be to generate lift. In doing so, as the air encounters the slightly swept wing, flows over it, and then off the trailing edge, the overall mass effect of the air is that it forms highspeed whirlpools of air at the wing tips. These are analogous to the wake of a boat that you can see. Now, there is also disturbed air behind an aircraft that acts like the propwash area behind a large ship. Both the 'propwash' and the 'whirlpools' generate turbulence.
The whirlpools of spinning air exist for a while as part of the standing wave (the wake) generated by the aircraft. If the wake turbulence was visible to the eys (it is sometimes when you land on a moist air day-- as a streamer) you would see a corksrew of air behind the plane. The contrail of a high altitude jet is more indicative of the 'prop wash' than the whirlpool.
Hope that helped.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.