Vortices

[yachtpilot]

What better place to ask this question ?
Some years ago flying night freight ( E110 Bandit ) into Frankfurt we had a rather nasty experience ...on approach to 27L ...737 ahead almost at touchdown and us 6 miles out....fierce winds ...50+ knts, 50 Deg off at 2000 ft.... suddenly we're out of control...doing a wingover and losing 7 to 800 ft breaking away to the left...turns out that there was a heavy 3 miles ahead on 27R and his vortex had been pushed across by the wind...I'd never heard of this during training or in any crew room chats...any of you excellant ATC types had experience of this happening... any of you aware that it could happen.. ?

[Jerricho]

Vortex can be a strange thing. I once had a MD80 7 miles behind an A340, slightyly north of it's track(wind was from the SE) and the MD80 was (in his words) "nearly flipped". Certain wind conditions just seems to make the stuff "sit".

[bookworm]

I would have thought that vortices wouldn't last long in a 50+ knot wind. The time when drifting vortices tends to be a problem is with lighter crosswinds with much less turbulence.

Sure it wasn't just the turbulence from the wind that caused the upset?

[vector4fun]

In the U. S., we're required to treat parallel runways less than 2500' apart as a single runway for wake turbulence separation, because of the chance of vortice drift. I don't know how far apart the parallels at Frankfurt are, but like the previous responder, I doubt a wake vortice would last long in winds like you mentioned. More likely just mechanical turbulence or nasty shear.

:confused:

[crj-jockey]

Dont expect the vortices to dissappear after a few miles. The separation should be applied to give the wakes some time to sink down. Consider this! I experienced some really bad wakes following heavy types about 5 to 10 miles ahead AND 1000ft below but almost never when cruising at the same alt.

[FWA NATCA]

In a recent wake turbelence (Vortices) training course the course stated that the Vortices will move laterally at approximately 2 - 3 mph. On parallel runways this is a real hazard.

The Wake Turbelence vortices will also sink approximately 1000 feet below the altitude of the aircraft that generated them.

Mike

[Spank me baby!!!]

There's an old TV documentary in the States that looked at the subject. They had tall poles on final with smoke generators fitted and the aircraft flew through the smoke on short final. You could see the lateral drift of the vortices which didn't seem to weaken at all. They also "vented" a leading jet at cruise and flew a second jet across it's butt. The second jet was thrown around quite violently. I think it was early in the B737 "falling out of the sky" period where they weren't sure what was causing the accidents and they wanted to rule out wake turbulence.

Personally, I've had a B737 descend through the level of a following Medivac C441. The B737 was 18NM ahead when he went through the level. Four minutes later the C441 reported encountering severe wake turbulence.

[yachtpilot]

Many thanks all of you who responded to the Q.... Seems there is still a bit to be learned about vortices.....certainly when I'm up at around FL350 in a Twin Commander or C441 ( where light turbo-props are a little bit sensitive ) I get a bit uneasy when a heavy passes a couple of thousand feet overhead...
once again...thank you for that..

[FWA NATCA]

Yachtpilot,

As long as the aircraft that is generating the wake turbelence vortices is 2,000 ft or more above you, you should be safe. According to the test that they have run, the vortices only descend 1,000 ft below the altitude of the heavy or large aircraft.

I would like to remind everyone that helicopters generate some fairly awesome vortices too.

Mike

[Bern Oulli]

I seem to remember a Zlin? having an ooh-nasty near Fairoaks years ago. Quite innocently minding his own business below the TMA. Got turned completely over by the vortex from a 747 passing overhead departing Gatport Airwick. The radar recordings suggested that the heavy was 4,000ft above at the time.

If they're gonna get you, they're gonna get you.

[yachtpilot]

,
Thank you NATCA... also for the PM. Well Bern, I'll just have to hope that the much thinner air at 350 keeps me out of trouble.
TY....