The worst case of turbulence?

[VMC-on-top]

I was chatting to a friend (now flies for BA) about various flying trips I'd done and was explaining about a trip a did back from Scotland down the East coast once. The forecast was not brilliant (and with more experience now, I wouldn't have done the same trip!). Winds were forecast 50kts over the highlands, gradually decreasing further South. Cloud base was approx. 3000. (I had no IMCR at the time so was stuck under).

We'd just passed North Berwick, a few miles inland from the coast. The trip had been relatively uneventful and the further South we got, the more relaxed we were until the aircraft suddenly dropped with a huge sounding "BANG". The drop was so severe, I was lifted out of my seat, hit my head on the roof, headset came off etc. We were both suitably shaken but unhurt by it.

The friend I was explaining this to had never experienced anything like this (certainly not in a light aircraft). It made me wonder what the very worst cases of turbulence might be - and also what might be dangerous to the aircraft and me!

[Genghis the Engineer]

Mainspar snapped and two killed in turbulence. (http://www.aaib.gov.uk/cms_resources/dft_avsafety_pdf_501463.pdf).

G

[IO540]

From the above report

The lack of precise evidence concerning the pilot's intentions and G-BVNA's flight path and speed after it turned inland makes it impossible to define the combination and degree of gust loading and manoeuvre loading which caused the failure of the wing. However, two related aspects may be relevant.
Firstly, although the workmanship in G-BVNA appeared to be of a good standard, a number of experienced aircraft engineers commented on the design of the wing structure. One observation was that, with the main wing spar not occupying the full depth of wing, the leading edge structurewould make little contribution to the tors ional stiffness of the wing and to the stability of the main spar. Another observation concerned the wing ribs, which were of simple 'trapezoidal' construction and appeared to have low in-plane stiffness. As the AAIB have not been able to contact the original designer, it has not been possible to discuss with him the structural design and whether, the static load test in Hungary was with a wing identical to that in G-BVNA.

i.e. hard to say... there are probably a lot of planes in this category which might not be that hard to break.

[VMC-on-top]

I should probably add that I was in a PA28.

[IO540]

Might be worth knowing exactly where they were and how high above the ground. It is quite possible to have a strong updraught near a hilltop.

[rusty sparrow]

Happened to me in the heatwave of '76. I was flying a glider at about 500' on final when a sudden bang pushed me down violently enough for dirt to rise up from the floor.

[Captain Smithy]

It's funny that this subject is brought up, as I've been thinking about this. Yesterday lunchtime I observed a low-wing SEP pass through the Edinburgh Class D, East-West, at about 1500 AGL (Chez Smithy ~ 400' AMSL), with the aircraft visibly being vigourously rocked back and forth in the (probably severe) turbulence. Couldn't believe that some nutter was up flying, despite the fact that the surface wind at the time was 25 Kt gusting 30-odd. At 2000' probably about 40+. Unbelievable. I would be interested to know how the landing went. Even from my perspective on the ground it was obvious the aircraft was being chucked about good and proper. Not to mention no doubt its occupants :yuk:

Round my patch things can get a bit rough if the wind is >15 Kt, plenty hilly terrain in the area to upset things somewhat.

Makes you wonder how severe turbulence can get before the structural integrity of the airframe is threatened. That report made for sobering reading.

Smithy :ouch:

[Jim59]

It is quite possible that you ran into a mountain wave system. Whist it is well known that flying in the wave is incredibly smooth - even when vertical currents are very strong - it is less well known that under the wave a rotor forms that can be exceedingly rough with complete reversals of wind direction within quite short distances.

The rotor turbulence may be harmful for other small aircraft such as balloons, hang gliders and para gliders. It can even be a hazard for large aircraft; the phenomenon is believed responsible for many aviation accidents and incidents including the in-flight break up of BOAC Flight 911, a Boeing 707, near Mt. Fuji, Japan in 1966, and the in-flight separation of an engine on an Evergreen International Airlines Boeing 747 cargo jet near Anchorage, Alaska in 1993.

Atmospheric rotors are intense low level vortices which form along an axis parallel to, and downwind of, a mountain ridge crest. They pose a serious aviation hazard and have been cited as contributing to numerous aircraft accidents.

Comments on wave flight in Black Mountains at URL below.

Wave flying (http://tinyurl.com/37tdtmr)

[Genghis the Engineer]

I should probably add that I was in a PA28.

I've certainly had my head bashed on the ceiling in PA28 sized aeroplanes, if nothing else it emphasises the importance of having tight lapstraps.

Just working from the certification rules and a bit of basic metallurgy and aerodynamics, a PA28 in download (which you had to bang your head on the ceiling) is likely to break at around -3g, but it is also designed that up to Va, which typically is a little above maximum cruising speed on a PA28, you should in theory hit a negative g stall at around -1.5g, which should more than adequately protect you from structural failure. Knocking yourself out is probably more likely.

That said, G-BVNA's accident discussion does highlight that you could make it worse with inappropriate control inputs - such as an inadvertent hard push on the yoke at the same time. This is pretty unlikely, but I'm pretty certain that if I tried hard enough I could break a PA28 that way.

A light aircraft however should be less vulnerable than a big aeroplane. Firstly we fly slower - giving poorer gust response (although they make up for that by having a higher wing loading, which does the same thing), secondly we have much less mass and so tend to accelerate all at once with the gust, third the g limits of a light aeroplane are typically about 50% better than those of a big jet.

G

[VMC-on-top]

It is quite possible that you ran into a mountain wave system

I was less experienced when I did that flight and with hindsight can't imagine how we weren't affected further North in Scotland. I now work on a rule of thumb that to avoid wave, I need to be (windspeed x 1000ft) above mountain or hill.

I recall we were about 1500-2000ft agl, winds were circa 30kts so if we'd been a couple thousand feet higher, would probably have been ok.

[Jan Olieslagers]

I need to be (windspeed x 1000ft) above mountain or hill.

So in 25kts wind you want to be at FL250, at least ?

[VMC-on-top]

It was a typo!

Windspeed x 100ft.

Everyone happy?

[Mark1234]

Worst turbulence - just outside Omarama in a duo discus, attempting a rotor climb in the lee of a big mountain range. Regularly off the seat, but too well strapped down to hit the roof. Utterly intimidating. At times the glider was almost 'fizzing' with some very strange oscilations where both tips were in lift, the middle in sink and vice versa. Most peculiar.

Spent the first 30 mins waiting for the wings to fall off and the next wishing they would - was quite miserable. Once the wave was contacted it was surreally smooth, and well worth it! In SEP terms, midday thermals over outback aus were pretty uncomfy, but nothing major. Worst big plane ride into Denver international one windy (50kt) day. I'd guess 'moderate' turbulence in ICAO classification, lots of crying and vommiting down the back, occasionally nearly off the seat.

[Jim59]

I need to be (windspeed x 100 ft) above mountain or hill.

That may keep you out of the rotor, VMC-on-top, (I don't know I've not met that rule of thumb before), but it has no chance of keeping you out of the wave which can in the right conditions go exceedingly high even in relatively modest winds.

The official UK record height in a glider in the UK (in wave) is 11,570 metres (37,958 feet) in 1995. I'm not convinced the wind speed was of the order of 379 kts!

P.S.: World height records in gliders are 12,637 metres (41,459') for a woman and 15,460 metres (50,721')for a man. Both in wave systems.

[IO540]

I think a crude rule is to fly 1000ft above ridges for every 10kt of wind aloft, for any downdraughts to be smaller than 500fpm.

This has always worked for me when crossing the Alps for example, which I normally do ~ FL180 (on oxygen) which is ~ 8k above the peaks (on the relevant routing) and I have never seen any significant turbulence for wind aloft values of say 20-30kt.

[gpn01]

It was a typo!

Windspeed x 100ft.

Everyone happy?

Far from it! That may work as an approximation for avoiding low level turbulence but it won't work for wave (and associated rotor). Mountain Wave can go as low as ground level and right the way up to the heights described elsewhere. In gliding you soon learn that wherever there's air going up, there'll be air going down too. You don't want to be in the downdraught near the ground or caught in between the opposing layers!

[IO540]

That's true but there are degrees of "turbulence", degrees of "mountain waves" (which exist anytime there is any wind flowing over ridges), degrees of "rotors" (comment as previous), and degrees of "wind shear" (which exists anytime one is climbing or descending with any wind present whatsoever).

Before I did my first flight over the Alps in 2004, I got all the usual dark warnings about "killer mountain waves". I think most of them were from armchair / pilot forum pilots. But knowing no better, I first flew to Wangen-Lachen in Switzerland and sat there for about 5 days, eating £20 sandwiches, waiting for wind-free conditions. Then we did the flight... being VFR, Zurich would not (completely pointlessly, as far as I can tell) let us into their FL130-base Class C so we flew most of the way across at FL129, getting nice pics like this (http://i101.photobucket.com/albums/m74/peterh337/samedan.jpg), and sure enough it was smooth. But other flights followed, and the other week I got this pic (http://i101.photobucket.com/albums/m74/peterh337/alps-2010.jpg) from about 5000ft above the terrain, with I guess about 20kt wind, and it was smooth too.

So I think reasonable rules can be applied.

What you do not want to be doing is crossing mountain ridges while flying at your operating ceiling :) Then, any downdraught is going to force a descent.

[Jim59]

I've just checked some of my glider's GPS flight recorder files for flight in mountain wave in Scotland, in the lee of the Cairngorms that are about 4,000' high.
I don't do much wave flying so I would guess that these figures are frequently bettered. The wind would probably have been about 40 kts at flying heights.

Climbing between 8,000 to 9,000' achieved around 1,000' per minute.

Climbing between 14,000' and 15,000' achieved around 600' per minute.

The glider used would have been sinking at at least 150' per minute at the speeds being flown so the air was rising at 1,150 and 750 ft/min respectively.

Sink at altitude was of similar magnitudes - although I did try to stay out of it!

[IO540]

Yeah, that makes sense, 4k above, 40kt, 1000fpm.

A great data point :ok:

40kt is quite a wind... not that common away from frontal weather. I once saw 80kt :)

[englishal]

You can sometimes see the mountain waves in the high level clouds, often 50 miles or more downwind. I've seen this in the lee of the San Bernadino mountains in LA when a strong Santa Ana wind has been blowing, and the (severe) turbulence has existed as far as Catalina Island. Makes for interesting flying.

There was a case in the US of a glider / tug combo meeting a mountain wave. The tug disintegrated, the glider landed safely and it is estimated that the g forces exceeded 14g.

[Coffin Corner]

The worst type of turbulence? In my humble opinion - Wake Turbulence. This very under rated effect is rarely examined in detail at PPL level by instructors & pilots alike. Make no mistake, this turbulence will kill you. I have been at the pointy end of an airliner and had 2 wake turbulence events. The first was so severe we had 4 uncommanded rolls of 50°-60° aob which we could do nothing about (6 miles behind an Airbus 330), then we were nearly shaken to pieces. Imagine if this was your average Warrior/Cessna.
Please people, if ATC gives you a "vortex wake, recommended spacing 4 miles" etc then please heed it.

CC

[bingofuel]

I agree wake turbulence is not well understood and rarely taught unless training from large airports.
The trouble with the guidelines of 4 miles or 6 miles behind the aircraft generating the wake vortices, is that the vortices dissapate with time not distance. In typical light aircraft 90-100kt speeds, 4 miles still gives you well over 2 minutes, and it is very unlikely you will close on the a/c ahead, so the time increases. But should you be following in a a higher performance a/c flying a faster approach , say 160kts to 4 miles, your chances of an upset are much greater, as 4 miles spacing is only about 90 seconds behind the generating aircraft.

[Coffin Corner]

bingofuel totally agree.

For example my other "incident" was behind a 744F, we were on a STAR and 35 miles behind this 744 with a 40kt crosswind. We hit the wake of this a/c and all hell broke loose, AP disconnected and it felt like we were flying through a thunderstorm again with uncommanded rolls. It chewed up the back cabin like they were in a washing machine, luckily nobody was hurt but it certainly was not a nice scenario to be in. The point of this one is that we were 35 miles ahead and we had a relatively strong crosswind but still hit it.

[vihai]

I think a crude rule is to fly 1000ft above ridges for every 10kt of wind aloft, for any downdraughts to be smaller than 500fpm.


Uhm... might work most of the times, but I was in a glider with light wind (10-15 kt) above 10000ft and good spring thermals.

The interaction between high-level wind and thermals created an unusual wave condition with climbs up to 2000 fpm at 16000 ft and sinks down to -1500 fpm nearby (but absolutely no turbulence).

Cumulus elongaten in lenticular clouds up to (estimated) 22000 ft.

[jellycopter]

I hit a bump so hard in my KIS that I thought I'd hit another a/c it was that violent. It was a virtually calm wind summers day and I was flying just to the south of Stanstead CTA at about 1000ft agl and 140kts. Everything was reasonably smooth, apart from the typical small lumps associated with differntial heating.

Without warning there was an almighty thump that fisrt pushed me into my seat then tried to throw me out of it. My pax hit the roof and split his head open, I'd have done the same probably but I'm a bit of a short-ass so had further to travel and the belts kept me in. I did smack my legs on the instrument panel though.

At the time, I'd never experienced turbulence like it before in 8000hrs flying so thought I might have hit another a/c or something. On arrival at my destination I was that concerned I did a fly by of the tower to check that the undercarriage looked intact - it was.

I put it down to wake vortex from a departing 'heavy' from Stanstead. I've since discovered that wake vortex can descend several thousands of feet below a heavy aircraft.

JJ

[Genghis the Engineer]

P.S.: World height records in gliders are 12,637 metres (41,459') for a woman and 15,460 metres (50,721')for a man. Both in wave systems.
Bit of an aside, but what on earth is the difference between men and women that justifies different gliding records?

G

[Union Jack]

Happened to me in the heatwave of '76. I was flying a glider at about 500' on final when a sudden bang pushed me down violently enough for dirt to rise up from the floor.

Rusty - Which is vastly preferable to dust rising up through the floor!:ok:

Jack

[IO540]

I've had a few bumps like that in clear air, flying near Gatwick for example. Probably a wake vortex descending. They supposedly descend at about 300fpm.

[Jim59]

Bit of an aside, but what on earth is the difference between men and women that justifies different gliding records?


A good question! There are also different championships for men and women at the international level. If I gave my personal opinion it might be thought to be sexist so if there are any lady glider pilots out there we would appreciate your views...

[Pace]

Two examples from my past one in a Jet the other in a twin.

Jet was enroute to Nice and we were given severe turbulence between FL 200 AND FL280 which makes a mockery of those who think you are out of danger high :eek:

I warned the passengers but not a ripple all the way down into Nice which was embarassing for me and the warning to the PAX.

We flew back empty on the more northerly SID out of Nice. passing 22000 feet all hell let loose with 45 deg wing drops, cupboards flying open. Luckely the jet was slow in the climb as she was almost uncontrollable.

I asked for an immediate climb to FL340 and at the level we were at in the Citation expected a rate of about 1000 fpm we were going up at 3000 fpm :eek: and held that all the way through FL300 into smooth air.

The second was in a twin flying UK to Malaga at FL120. I was single pilot and picking my way between two storm cells near Madrid with ground temperatures at 45 degrees.
In clear air between the cells the ASI went in a flash from 155 kts IAS to 70 kts IAS. I punched out the autopilot went for full power forward on the column and NOTHING.

Same attitude same IAS. Nothing I did made any difference and the
aircraft felt as it had flown into a vacuum!!! I had never experienced anything like this before sitting there with over 2000 fpm on the VSI going down like a lift.

At FL090 after dropping 3000 feet the controls came alive. I informed ATC and climbed back to FL120 as if nothing had happened.

So BEWARE :E

Pace

nb have reported both of these here before

[gpn01]

A good question! There are also different championships for men and women at the international level. If I gave my personal opinion it might be thought to be sexist so if there are any lady glider pilots out there we would appreciate your views...

It's not just gliding. FAI World Aerobatics Championships (power) has a Men's winner and a Women's winner.

[cats_five]

It's easier for men to arrange a suitable pee system than women?

Dunno, ask the IGC & FAI.

[Intercepted]

Quote:
Originally Posted by Jim59 http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/private-flying/420768-worst-case-turbulence-2.html#post5805929)
A good question! There are also different championships for men and women at the international level. If I gave my personal opinion it might be thought to be sexist so if there are any lady glider pilots out there we would appreciate your views...

It's not just gliding. FAI World Aerobatics Championships (power) has a Men's winner and a Women's winner.Women and men should obviously compete in the same championship and the only sexists must be the various organisers of those events.

If I was female I would refuse competing in a separate class for women. This has happened before in other sports. Annika Sorenstam (Golf), Judith Polgar (Chess) etc.

[Genghis the Engineer]

Got me wondering, it seems that FAI have separate classes for...

Ballooning (http://www.fai.org/womeneurohab)

Class D gliders (http://records.fai.org/data?v1=275)

15m gliders (http://records.fai.org/data?v1=276)

World class gliders (http://records.fai.org/data?v1=277)

World class gliders (http://records.fai.org/data?v1=277)

Parachuting (http://records.fai.org/data?c=9)

Manpowered (http://records.fai.org/data?v1=178) (Okay, I can just about understand that one, men do usually have a bit better power to weight - hence different olympic classes.)

Hang gliding (http://records.fai.org/data?c=10)





Except that looking closer, they're actually divided into "feminine" and "general" - so effectively there's an open class, and then a separate class for women only.

Seems rather like something out of the 19th century.

G

[IO540]

Seems rather like something out of the 19th century.

Indeed, but I bet that for every woman who genuinely wants to compete in a mixed category there will be a few who want a "women only" category. Just look at other walks of life: Womens' Institute, all the support networks for women, etc. It is everywhere. Somebody must be into continuing this division pretty heavily otherwise it would not survive. I think a lot of women want to walk in their own non-patronising area and for example the good looking ones don't want to be accused of getting preferential treatment (which of course they would get, usually ;) ).

And yes it is far easier for men to pee into a bottle (I should know; I am an expert by now, with flights up to 7hrs) but I gather the chemical (silica gel) alternative levels the field pretty well.

[Redbird72]

Apologies for moving back to turbulence, from women-only gliding and pee :oh: but there's an interesting incident in this month's AAIB report regarding possible effect of wake from a "light" heli on a PA28:

http://www.aaib.gov.uk/cms_resources.cfm?file=/Piper%20PA-28-140%20Cherokee,%20G-BRWO%2007-10.pdf