New Clues Deepen Flight 587 Crash Mystery

Now, my question is this...why no reports of eyewitnesses who spoke quite definitively about flames and smoke near the wings. Or did I miss this in the article. Again...only airline pilots and ground crews are credible eyewitnesses? Check out any news footage of interviewing the people who actually saw the thing go down. There's plenty of 'em. Everyone says flames and smoke.

flames and smoke are possibilities. What matters is the time sequence of when they saw them. Seeing flames and smoke during the final moments are inconsequential in one respect.

So what exactly is wake turbulence, or wake vortex? All aircraft generate vortices at the wingtips as a result of producing lift. The heavier the aircraft and the slower it is flying, the stronger the vortex. Vortex size also increases with wingspan, and some aircraft - eg the Boeing 757 - are known to produce particularly vicious wake turbulence. The vortices descend relatively slowly until they decay or reach the ground. Typically, for each mile behind the generating aircraft the vortices will have descended between 100 and 200ft. These vortices generally persist for up to 80 seconds, but in light or calm air this period can extend up to two and a half minutes.

An encounter with wake turbulence can result in severe upset to the equilibrium of the aircraft, with rapid uncommanded movements in roll, pitch or both. Generally, the lighter the aircraft the greater the degree of upset. A Cessna 172, for example, is vulnerable to the vortices generated by a similar size of aircraft, although such an encounter will usually be uncomfortable rather than life threatening. An encounter with the vortices generated by a jet transport is, however, another matter.

Vortex encounters in the cruise, as in the two examples detailed above, represent a minority of this type of accident, which usually happens in the landing phase. An encounter with the preceding aircraft's vortices when on short final - or even when on the ground but still rolling - can result in a loss of control from which recovery is not possible. A search through the NTSB accident database for 'wake turbulence' will provide many examples.

Vortices are invisible - although occasionally in very humid conditions the cores may be seen. You need to have a good mental picture of their likely location. In the cruise, aim never to pass behind and below a heavier aircraft. If flying in the circuit with other light aircraft, fly at the proper circuit height, allow a sensible spacing and be aware of the position of possible vortices from departing aircraft.

If on approach under ATC control they will space you to avoid the wake of the preceding aircraft, but on many occasions you will have to make your own judgements. Generally, allow plenty of distance - use runway length as a visual guide if it is in sight. Allow up to six miles behind a 'heavy' - and remember, vortices drift downwards, so if you stay above the path of the vortex-generating aircraft you will usually be OK. (Your light aircraft can cope with a steeper angle of approach than the standard 3 degree glide slope of an airliner). When landing, land beyond the touchdown point of the heavier aircraft - vortex generation stops when the nosewheel touches the ground.

Remember also that vortex generation begins at rotation, so vortex avoidance on departure is also important. For example, a light aircraft departing after a Boeing 727 should allow a minimum of two minutes - and more if taking off from further along the same runway.

Finally, beware helicopters - these can generate more intense turbulence than fixed wing aircraft of the same weight.

For further information on wake turbulence, read the FAA leaflet 'CAUTION - Wake Turbulence'.

I think the rattling noise was some guy with an air wrench. (Didn't you ever see the episode of Twilight Zone where a guy was out on the wing tearing off parts of the plane?)