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Wake Turbulence? I Doubt It. Per the cockpit voice recorder from AA 587, the crew suspected wake turbulence, and "airframe rattle" is heard at two points on the recording. I don't know what wake turbulence feels/sounds like in a large airplane, but from first-hand experience with wake turbulence in a small airplane (Piper Malibu) I can tell you that there's no "rattle." It's extremely violent and sounds/feels more like a sudden impact or even an explosion. (We were convinced we'd hit another airplane.)
Wake turbulence is generated from the wingtips of any aircraft. Lift causes the creation of horizontal vortices--little tornadoes--that trail the airplane. When viewed from behind, the left wingtip vortex rotates clockwise, the right vortex counter-clockwise. In calm winds, the vortices sink at about 500 feet per minute, so one cannot encounter wake turbulence unles one is somewhat below the flightpath of the preceeding airplane.
Using radar recordings, the FAA and NTSB can reconstruct the position of the wake turbulence vortices and their relationship to the flightpath of the following aircraft. In my case, we descended into the downward (inside) side of a wingtip vortex from 90 degrees to the flightpath of the previous airplane, a McDonnell Douglas MD-80. Radar showed that we then dropped 700' in only four seconds. That's a heck of a jolt.
I'm no accident investigator, but I think the crew's guess of wake turbulence is a red herring. The most interesting clue so far is the relatively-impact vertical stabilizer (vertical portion of the tail) that appears to have departed the airframe before other things started going wrong. Once that happened, the nose would have pitched down, and in pulling it up (particularly in a turn, where G-forces are increased), the loading on the wings and wing-mounted engines could have exceeded design limitations. The latter is pure speculation. The real issue is what caused that vertical stabilizer to come off of the airplane. Of course, that could be wake turbulence after all.
Posted Wednesday, November 14, 2001 11:49:51 PM 
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