My question on the A38x is more related to inflight – I always reckoned on 10 miles and 1000ft but wonder if this is enough as they generate so much wake turbulence.
How often would you end up flying on the same trajectory as an airliner in cruise?
There are no airliners below about FL200 except in terminal areas (the Gatwick – Brussels A320 flights were FL190 or so).
In terminal areas, a very different thing. But it seems to me that even there, on arrivals at least, the CAT-GA trajectories are not normally overlapping in space and with a short time gap.
Departures are the most dangerous thing.
I am often cruising below and on the same track as an airliner and it always makes me nervous. I had always focussed on slow, high-AOA situations like the terminal area in particular takeoff and landing but read Les Abend’s story in Flying and have reassessed somewhat.
http://www.flyingmag.com/pilots-places/pilots-adventures-more/jumpseat-assaulted-a380
Interesting story!
I didn’t know they spread sideways also. 5 miles is a helluva spread. How much distance or time is needed for that? @chrisparker might know about this…
Peter wrote:
How often would you end up flying on the same trajectory as an airliner in cruise?
It does not have to be the same track – crossing gives you 2 chances of hitting the vortex. Operating from EHLE Lelystad we are often crossing below the approach paths at EHAM Schiphol with vertical separation usually below 2000ft. I was a pax in a TB20 that hit the vortex of a 747 – that left me shaken, my own experience with the Citation outlined at the beginning of this thread was pretty terrifying. Is an encounter with a vortex from something as big as the 380 survivable in a light aircraft? I have my doubts. Re-inforced by JasonC’s link.
Departing my home field Santa Monica (KSMO) to the east, there is one track that runs pretty much right below one of the arrival tracks into LAX. On one occasion I was being overtaken by an A380 (didn’t see it, was coming up right above me) and ATC vectored me away, clearing me to climb into the LAX Class B, IOW got me above and sideways away from the vortices. As the arrival routes for all of the LA area airports are about to be changed, it’s probably a good idea to be extra vigilant.
I have just read that the Challenger 604 (in post #39) was written off by this wake encounter.
So just think what would happen to a TB20
All these stories remind me of my first (and hopefully last) encounter with wake turbulence…
Was flying around Florida with my freshly minted license with some friends in tow. We were trucking along at about 4500’ AGL (nearly same thing as MSL in Florida) and heard a military ‘heavy’ on the radio.
We saw it about 10-15 miles ahead and the giant quad-prop plane flew roughly across our flight path at about the same, or perhaps a little above our elevation. With 3 pilots onboard, we all discussed the big ‘no-no’ of wake turbulence, steadying ourselves for the next few minutes, and climbing to be safe.
Nothing happened.
So we chatted, and settled in and forgot all about the ‘heavy’ as it was long gone.
Then it happened.
About 10 minutes later, the floor fell out of the airplane and a hammer came down on top of it.
We were slammed down a hundred and fifty feet in a second or two. It felt like the wings had come off of the airplane at about 10 feet and the plane just fell onto a runway with no gear down.
With bumps on our heads, and gritted teeth, we were looking around for the disaster, wondering which wing fell off or what just happened… we hadn’t flown into a cloud… right? Nope. The air was once again smooth, and we were about 250’ lower than we started… (iirc)
Right… Wake Turbulence.
We had flown into it about 10 minutes after the giant prop plane had passed our nose. The vortex hadn’t settled much at all…
Free conehead hats and farmer shorts to match our greenhorns…
So just think what would happen to a TB20
A good Q, but effects of turbulence are worse at higher speeds, and the Challenger was probably doing something like 400+kt TAS. If you entered the same wake at 150kt the acceleration on the aircraft (and the stress) would be much less – for a given value of wing loading. So while the wing loading of the Challenger might be 2x that of the TB20, it was going a lot faster. I am not sure whether the relationship is linear; I have a feeling the acceleration is a square of the speed, so 400kt would be 7 times greater for the same wing loading.
