Dreadful accident - should have been avoided

[dalgetty]

There was a terrible accident in Backnang-Heiningen in Germany back in 2012. The relevant air authorities made a video explaining what happened, which is only available in German.

I edited it into a shorter version with English explanations.

Please have a look, it contains valuable information for anybody flying light aircraft:
https://www.youtube.com/watch?v=KXlv16ETueU

[rnzoli]

Wow, thanks!

Correct me if I am wrong, the 2-minute wake turbulence separation is applicable to landings as well.

Another grave danger is helicopters (downwash).

[enq]

Well done, good post, surprisingly strong vortices generated from an aircraft that I would not intuitively consider presented such a high risk.

[Echo Romeo]

Wow, that is quite shocking, thanks for posting.

[Shaggy Sheep Driver]

I'm surprised an AN2 produces such strong vortices.

[dalgetty]

Good point about helicopters. In Lausanne we've just had the addition of a bunch of helicopter hangars, it can make life interesting. Two minutes is not all that long

[Oldpilot55]

ISTR 757s produced extremely strong vortices that flipped fairly large jets.

[Shaggy Sheep Driver]

757s were notorious - I think they are better now they have winglets. I remember seeing them go over Mobberley on short final for (the then) 06 at EGCC, and several seconds afterwards came the most eerie whistling and cracking sounds of the vortices. No other jet, even 747s, did that.

[Gertrude the Wombat]

Two minutes is not all that long
It's £6 to a rental pilot.

(But yes, when ATC tell me to wait for vortex separation I'm perfectly happy to do so.)

[Mark 1]

It has happened before. I well remember this accident.
https://assets.digital.cabinet-office.gov.uk/media/5422ef16e5274a1317000261/dft_avsafety_pdf_500836.pdf

[Shaggy Sheep Driver]

I used to operate a Chipmunk from a major airport, so vortices were always a threat. ATC would say to me (holding on base, 1 mile out) "cleared to final behind the landing 737. Recommended spacing is 6 nautical miles". If I'd trundled downwind away from the airfield and then turned base to allow that 6 nautical miles spacing, I'd have lost my place in the queue to the next instrument inbound down the ILS.

Vortices are generated at the wingtips, while the wing is at a positive AoA. They move outwards and downwards (and of course move laterally with the surface wind). So, if you join final above the flight path of the 'heavy' (easy 'cause they are on a 3 degree glidepath and I can come in much steeper) and remain above their flightpath, and touch down after their touchdown point, you won't encounter vortex. So that's what we did. It often resulted in a 'land after clearance' on short final!

[rnzoli]

I brought this over from our local discussion forum - a very scary stunt, where an An-2 tows 5 gliders onto an airshow. THe 5th pilot at the rear is constantly swearing about the lack of sufficient aileron authority due to the wing vortices.
I believe this stunt was only possible as the gliders wings reach out from the vortex, giving them a little bit of control authority / stability.
mkfceTLpuKY

[9 lives]

Two minutes is not all that long

It's £6 to a rental pilot.

Yeah, but the time is still going in your logbook...

I was once flying somewhat line astern in my 150, behind a buddy in his 150. His vortex stood me hard on my wingtip, and spit me out - I learned! Same weight aircraft is all it takes to put you over. If not "at altitude", you're in big trouble!

Vortex avoidance is one thing which a good crosswind greatly aids. Many has been the time I have satisfied myself as to the direction that the vortex has been blown, and I've operated well to the upwind side, with no problem. In the video clip, it is apparent that there is little to no wind, so the vortexes will just hang there stationary, until the dissipate - probably in £6 or so..... ;)

It's interesting to observe while a pax in a window seat, behind the wing on an airliner, that once a whole lot of flap is extended, the vortex is generated off the outboard end of the flap, rather than the wing tip. This has negligible bearing on avoidance though....

[Machinbird]

Way back when I was going through Navy flight training I had a wake turbulence experience that could have ended badly. The solution used to counter that problem applies well to a wide range of aircraft, so please take note:

I was number 6 in a flight of 6 aircraft on an air to air gunnery mission in T-2A jets. The first four aircraft took the runway in echelon 1000 feet down the runway, and the last two aircraft remained at the runway end in echelon. Per the briefing, the individual aircraft rolled at 10 second intervals.

When it was my turn as #6, I applied full power and performed a normal take off, raising the gear and accelerating. At 50 feet above the runway, the aircraft began to roll until it was standing on its right wing tip despite application of full left aileron and a bootfull of left rudder.

What do I have left I asked myself? Ejection was out of the question with the older ejection seats. The aircraft was not going to fly many seconds more in that attitude.:eek:

I pulled back on the stick which turned the aircraft away from over the runway and in seconds I was in control again.

The fix was simple. All I had to do was throw out the mental concept of remaining over the runway. I hope this little story helps others.

[DeltaV]

...a very scary stunt, where an An-2 tows 5 gliders onto an airshow...
Dear god, that looks scary. You say that was for an airshow but it couldn't be a one off, they'd have to practice, so did the team ever lose a glider getting snarled up in another tow wire?

Not at all a 'heavy' but I once was surprised by the strength of the vortex off a friend's Condor.

[The Ancient Geek]

The AN2 is a nasty case because it has a very short takeoff run so any following takeoff is going to be below it and in the falling vortices.
Add that to the fact that it weighs in at around 5 tons and you really need to leave a good 2 or 3 minutes before following.

[Peter-RB]

What a good thread,

Wake turbulence and ground air current are something that all of the PPL Pilots FW and Rotary should read up on and fully understand, I trained initially on R22/R44 and they are really twitchy when being even 3 mins behind anything else..

Good videos as well, well done for the attention this needs.:ok:

[RatherBeFlying]

I flew a Citabria at a helicopter training field and came back when a Schweizer trainer was doing hover practice 50 yards to the side of the runway.

There's quite the wake, even from a small helicopter.

[cumulusrider]

Try 9 gliders on tow.
Vortices from that lot?
LiveLeak.com - One tow plane + 9 gliders (comments)

[rnzoli]

Jeez, that's insane! :) Even thought the Turbo Cmelak is under 2 tons, so creates slightly weaker turbulence than an Antonov-2 biplane.

It's good to see the formation from the side-view. The first 6 appears to be above the wake and the last 3 (with the greatest distance) suffer the most from it.

I guess the music is put on to supress the swearing and cursing and F-words :)

[roulishollandais]

I pulled back on the stick which turned the aircraft away from over the runway and in seconds I was in control again.

The fix was simple. All I had to do was throw out the mental concept of remaining over the runway. I hope this little story helps others.Your experience is easy to include in the basics, and so precious ! I hope our regulators and flightcheckers will read and follow your wise example without delay :ok::ok::ok:

[Pace]

Not sure how accurate or representative that test on the AN2 was
The aircraft descended then would heve made a big pitch and power change to go to a climb.
I don't know enough about vortices generation? When they are at their maximum but this AN2 took off on a steady climb maybe 30 seconds ahead of the crash aircraft.
A true test would have had smoke emanating from the crash point and the aircraft 30 seconds ahead.
Again in the high altitude tests the AN2 should have been in a climb attitude with the chase aircraft 30 seconds behind which it was not on the test.
But a good example of taking off behind a much larger aircraft and the dangers of doing so.

Pace

[9 lives]

I've had several occasions in the last few days, where consideration of wake turbulence was necessary for safe flight, both landing behind, and taking off after another aircraft. In the case of landing (behind a departing Dash 8) I recognized it as being appropriate to land short, and be firmly on the ground before its rotation point. In a few other cases, considering the crosswind, to assure all of my operations were upwind of the location of the expected wake.

As long as you are comfortable about list moment maneuvering, it's entirely fine to approach or depart offset to the runway centerline, to avoid a wake turbulence area.

[Pace]

Also

With any threat of downdraughts speed is your friend so don't climb away hanging on the stall! If the runway is long enough rotate at a slightly higher rotate speed

Pace

[The Ancient Geek]

The problem is wake vortex turbulence not downdrafts.
The vortices naturally decend so staying low is a bad idea.
Rather give them plenty of time to dissipate and use best rate of climb speed to get above them.

[9 lives]

Rather give them plenty of time to dissipate

Yes.

and use best rate of climb speed to get above them.

Ahhh, not so fast... Yes, above wake turbulence is the most desirable place to be, but trying to get there can end badly. Most of us do not fly aircraft with that kind of climb capability. I will not fly through a zone I think could contain wake turbulence, so I would not be climbing through it! I will be either waiting the full wait, or determining a path which will take me around the risk area, not through it!

The tactics of wake turbulence avoidance are well documented, and worthy of review.

[Shaggy Sheep Driver]

In a light aircraft if taking off behind a jet transport at a large airport it's no problem to get airborne well before the point that the jet did, and then turn left or right immediately climbing out at close to 90 degrees to the runway heading (with ATC permission of course).

We used to do this, and ATC appreciated it as it helped keep up the flow rate.

[piperboy84]

I have often wondered about wake turbulence away from the immediate runway. In Los Angeles some heavy commercial traffic inbound route over the SMO VOR fly downwind east to downtown LA, turn base south towards Long Beach and final back towards the LAX, there is a VFR route directly below the base leg that tracks the LA river (the schwartznegger one) with an altitude restriction of 1700 if I remember correctly, however the CAT turning final appear no more that 2000ft above the transiting GA . What is the safe vertical clearance to allow WT to dissipate in a no wind situation from slow and heavy CAT? I read a story in Canada I believe where a GA transiting a terminal area was vectored below a jet and had a in flight break up due to WT.

[FullWings]

What is the safe vertical clearance to allow WT to dissipate in a no wind situation from slow and heavy CAT?
I don’t know how far away in time and distance you need to be to be “safe” (it depends on your aircraft) but I have experienced serious wake 1,000’ below and 5 minutes after a heavy jet. I suspect in ideal circumstances it could go much lower/longer.

I think atmospheric conditions play a large part: vortices appear to last much longer and keep intensity in a stable layer or where there is no preexisting turbulence.

[9 lives]

You can encounter wake turbulence in any part of the sky, from any preceding aircraft, though at higher altitudes, and your flying faster, the effect will be more manageable. I'm very pleased to hit my own wake turbulence following a well flown loop.

Encountering wake from a "heavy" ahead of you should always be considered, and avoided, but if you're flying at Va or just slower than, and a thousand feet or so up, you'll have a chance to limit it to a really rough ride, rather than being slammed out of control into the ground.

[Pace]

I still stress with any down draughts wake turbulence or other wise you do not want to be hanging in the sky near the stall.

Taking off with that possibility even turning to avoid i personally would get the aircraft cleaned up quickly and some excess speed in case you need that extra energy. Remember its not just wake turbulence which can cause air currents which will slam you into the ground I used to operate at an airfield where the winds from a certain direction would curl over a hanger with the same effects

Hitting wake turbulence at high speed is a different matter. I am sure we have all experienced that crash with air currents caused by unexpected wake turbulence from another aircraft and there excess speed is your enemy

Pace

[rjay259]

http://www.caa.co.uk/docs/33/20130121SSL15.pdf

I'm sure most have found this anyway but it gives some useful info.
Having been hit with wake turbulence in a 737 and we were following a 320 we rolled 30 degrees very very quickly.

Scared the poop out of me and the skipper.

[hum]

l8EwvDTJeNs

[Shaggy Sheep Driver]

It might be obvious but I'll point it out anyway; WT is far worse when the generating aircraft's wing is at high alpha, with a big pressure difference between lower and upper surfaces. So much more danger fom an aircraft landing or taking off than from one in the cruise

Hence the danger is a double whammy - WT is far more serious from a landing or taking off aircraft, and by definition if you hit it then you are low down and slow.

[Pilot DAR]

To further Shaggy's thoughts, and more for amusement than useful, I have noticed as an airline pax, that on final, with lots of flap out, the wingtip vortex has moved from the wingtip, to the outboard end of the extended flaps. A retired aerodynamisist friend confirmed that the wingtip vortex is not always produced at the wingtip.

In any case, understand where to expect them, and actively avoid!