curious

I see that the thread on Monday's crash is gone, so I have to start a new one. I'm wondering if anyone with real knowledge can help answer a question I have. All latest report's on Monday's crash are focusing on the fact that the AA plane took off less than the recommended 2 minutes (1 min, 45 seconds), after the Japanese plane before it. My question is, who decides when that plane takes off? Do the pilots get the go ahead from the control tower, as I always thought, or do they make the decision when to leave themselves. And if there is such a real danger in not heeding that 2 minute window, why on earth not wait the extra 15 seconds? That is what is truly puzzling me. Any pilots out there that can comment?

skyking

I'm not a pilot (but I play one on TV). But I have been in the cockpit and listened to the transmissions between the pilot and tower. In my experience, the pilot always has to wait for the go-ahead from the tower before entering a runway for takeoff. And consider this: Can you imagine the chaos if the decision were left to the pilot?

curious

I agree! It just seems that if (and I emphasize if), the cause of the accident could have been easily prevented by waiting 15 seconds, why was that procedure not followed?

Sabotage

I'm still not convinced. I would think that the last 15 seconds of the 2-minute window would be the least turbulent. The tail fell off right after take-off. It still sounds like it is worth investigating sabotage to me. The tail fittings were inspected in December 1999. The investigators have not ruled out sabotage.

Mark

Pilots do get there go ahead from the control tower, but they can make special requests to waive certain types of circumstances such as what happened on Monday with a plane taking off and they not waiting for the "recommended" time before departing. The 2 min rule is for what is called "wake turbulence" which is a free-moving vortex core generated behind an aircraft by the high-pressure air beneath the wing swirling up and around the tip to meet the area of low pressure on top of the wing. The vortex dissipates with time which is why planes are encourged to wait the two min to minimize most of this high pressure air.

skyking

It's me again, and again from my experience, I don't think Sabotage's depiction of turbulence is the way it exactly works -- it's not about hitting the "last 15 seconds." It's more about advancing into the previous plane's wake of turbulence.

I'm not trying to rule out (or include) sabotage as a cause, but the fact remains that no responsible pilot would enter a runway with the tower's OK, and in fact a good pilot woud refuse to enter the runway inside the window of turbulence.

Last point: From my experience and conversation with pilots, I'd say their biggest complaint about the 2-minute window is that it's so much exceeded at most aiports. Often, a pilot has to wait for far more than 2 minutes before advancing onto the runway, just because the guy in the tower is so busy and takes a awhile to get back to the pilot.

Tom

From what I read the turbulence can be like a horizontal tornado and can rock the plane back and forth severely. If the tail already had metal fatigue, any severe rocking motion could have jarred loose the tail section. As to the maintenance inspection a couple of days before, it was a walk around and the tale was not closely inspected for metal fatigue, loose fittings etc.

ASmith

I have an excellent article on wake turbulence, if anyone wants the article, email me.

curious

OK, given that this "wake turbulence" phenomenon is widely known to be a potential danger, why would that flight have taken off in 1 minute 45 seconds after the previous flight as it was reported to have down? Could it be that this accident could have been prevented by simply waiting a few more seconds before taking off? If so, I can't imagine why it would even be an option for pilots to even think about taking off without leaving at least 2 minutes between flights.

John

Wake vortex turbulence is a known risk element in aviation operations, but like clear air turbulence (which can be equally violent but is usually encountered at an altitude high enough to permit recovery) it's not a precise science. The separation rules adopted are approximations and pilots are well trained in dealing with wake turbulence operations. And just because an airplane is larger doesn't mean its wake is more dangerous - a lot has to do with various design elements - wings, etc. Some smaller jets have a reputation of producing worse wake turbulence than the JAL 747-400 which departed before the AA flight. Even helicopters have been faulted for leaving wakes which led to aircraft accidents.

But only a very few accidents have been shown to have been caused by structural failures induced by wake vortex turbulence, so we should let the NTSB do its job and not be fearful; this is in all probability a freakish event which, while tragic, is not likely to signify immediate hazards to other flights.

Matt

It appears that air traffic followed procedure when it cleared the JAL 747 to take off and the tower clearance was 2 minutes and 20 seconds apart. However, there was a delay from the time the JAL plane got clearance to take off and the time it actually did so. The NTSB believes the actual time was 1 minute 45 seconds. The JAL plane was approximately 800 ft. above AA587, but the wind pushed the turbulence lower. Experts say the wake turbulence could have struck the AA plane with tornado like force. IF you have ever been near or in a tornado, you know that's pretty darn powerful.

L

Today's media are reporting NTSB believes the plastic attachments for the tail separated ... reason unknown. AA will examine the balance of the A-300's. BUT the JAL vortex could have been the causative factor ... given reconstuction of altitude, wind direction and time, plus AA flight path. Tail probably separated first ... accounting for loss of control. With the evidence so available, it seems like NTSB will warp this up soon. If this was sabotage, it will be interesting to learn (and prove) exactly how it was accomplished. If this had occurred pre-11th, we'd all be thinking accident, and wondering what the heck FAA was going to do about it. Ciao

L

Make that "wrap" ... or stay with warp ... your choice. Ciao

Gerry

The general manager of the San Francisco International airport(also a pilot) said prior to yesterday that weight vortex turbulance is a well known risk. He said that because of it, when an aircraft takes off behind another aircraft the second aircraft is always put on a higher flight path than the first aircraft. This is because the weight vortex always goes down. The AA aircraft at JFK was put on a flight path below the JAL flight. Interesting?

JustMyOpinion

If it turns out that vortex turbulence alone is enough to make the rudder and tail break off cleanly, I'll be very surprised. There's more here than meets the eye, whether it be faulty mounts or sabotage, but something's up.

Matt

From what I understand, the AA plane was below the JAL one because of the wind speed. And, why are they using plastic attachments on a tail???

xx

They probably use plastic attachments because they are better. Some plastics are very strong and better for certain applications than metal. Plastic doesn't always mean cheap and flimsy.

Bert

The issue was not the separation time between the planes. That (meaning less than 2 minutes) happens every day, hundreds of times a day at numerous airports. That really is not unusual, nor is it a compromise on safety.

Commercial airliners are much more durable than people think they are, as are certain plastic components. (Plastic is used because it is light, thereby reducing fuel consumption.)

The issue here was with that specific plane which may have been built with fault in the tail section. In almost every case, a plane would have flown through the 747 turbulence without even a second thought.

Don't get to wrapped up in what the media says on these issues. They tend to overplay things and sensationalize them because controversy, real or perceived, makes for great television.

Bottom line, this was a freak occurance on a specific plane that had problems.

skyking

The word "plastics" itself is a little misleading.

The engineering term is "composites," which essentially means it's a man-made substance. If you insist on "plastic," then you probably also have to say that the heat-shield tiles on the space shuttle are made of "plastic."

Matt

According to the aviation experts the problem with composites are that it is extremely difficult to detect metal fatigue in them. In 1988, the year this particular airbus was built, the composites frayed and seperated and had to be repaired. If the composites were fatigued, the wake from the JAL plane could have caused them to snap off.