Think I learnt about flying today...

[MayorQuimby]

Originally Posted by IO540

I don't see how a downdraught can force a plane into the ground.

I guess as soon as you're flying upwind it can. I can see what you're saying as long as you're flying downwind, although that probably assumes nice non-turbulent flow.

I imagine too that people have been caught out by believing they could go over a ridge in a windward direction because they were above the ridge to start with. In this situation they may not have had the climb rate to maintain their altitude as they approached the peak, cutting through the descending airflow.

MQ.

[dublinpilot]

Some people like to fly without GPS, some people like to look out the window, some people like to use a map occasionally.

There are times when the GPS comments get really tiresome Peter - give it a break PLEASE!

I've just realised Chilli is absolutely right. In a way it's ridiculous to set yourself up like an airliner - we're mostly PPLs for god's sake, let's have a bit of fun.

Oh come on guys. IO540 never said that coodem (or anyone else) should always fly with a gps. He simply, and correctly pointed out, that turning it on after an inadvertant entry into IMC at low level was far far too late.

Does any seriously think that a VFR only pilot (and I'm assuming coodem is from his post) who has entered cloud at low level should be turning around looking for his gps on the back seat, then trying to fiddle around with it?

If he had it with him and turned on before the flight then it could be a big safety aid in the situation described.

If you carry a gps for the purpose of helping you out in an emergency aid then have it set up so that it can aid you if that emergency comes along. We all make sure that we wear our life jackets, and have the life raft close to hand when flying single engine cross water don't we? It's ready to go if needed.

If you enter cloud low level, VFR only, and the gps is in your flight bag, then I think you've already missed the boat as far as GPS goes. Forget about it, fly the airplane and use whatever you have to hand. That maybe a predetermined safety altitude, and tuned in vor, or simply the radio to call a radar unit for help. Trying to find and turn on a gps at this point is only going to disorient you.

If you carry equipment for an emergency then have it set up. If you don't, then don't distract yourself with it in the emergency.

dp

[englishal]

The thing is....if you have the forsight to carry a GPS, then why not have it switched on. Fine if you want to dead reackon your way around the land (or as Enerst K Gann said after using radio navigation: "we had to revert back to this old outdated dead reckoning" and this was possibly in the 40's )....If you don't want to use it then either turn it away from you, don't look at it or leave it at home.........

A spare battery is no good for your torch if it is in you bag in the boot, or as I found out, there is no point leaving your approach plates in the bag in the luggage compartment just because the weather is *forecast* to be VFR....

[IO540]

I guess as soon as you're flying upwind it can. I can see what you're saying as long as you're flying downwind, although that probably assumes nice non-turbulent flow.

However, in the "flying next to a mountain" scenario you won't be flying upwind or downwind. You will be flying across the airflow (i.e. parallel to the mountain face). The wind is coming down the mountain, so if you did fly upwind you would fly into the rising ground (not good).

I imagine too that people have been caught out by believing they could go over a ridge in a windward direction because they were above the ridge to start with. In this situation they may not have had the climb rate to maintain their altitude as they approached the peak, cutting through the descending airflow

Absolutely agree. I just couldn't see how descending airflow could force a plane all the way into the ground - unless there are other factors.

As to those having a go at me over suggesting that a GPS should be switched on if it is being carried at all, I am suprised as some who did should definitely know better. A GPS in the bag, not switched on, is about as much use as a chocolate teapot.

I am trying to write stuff that expands knowledge on a subject. If everybody did the same it would be helpful all around. If somebody disagrees, it's better to post a good reasoned argument which I can learn something from, not Oh for F*CKS sake!

[Piltdown Man]

I believe Mercenary Pilot is right, it was mountain wave which was to blame for your predicament, or in your case, the rotor which is an associated phenomenon. And these things go down to the ground! In a glider, you often end up putting on as much speed as you can and fly into or directly down wind. In a powered aircraft I'd do the same (and I have done so!), but with full power!

What you missed was "wind and mountains" however cities lots of large buildings do very similar things. I bet you won't miss these two again.

PM

[SAR Bloke]

A downdraught can easily throw you into the ground. It is true that one of the escape methods for downdraughting is to head to lower, flatter, ground as the air will usually (but not always) become more laminar and may enable you to climb out of trouble. Turbulent air can do funny things and you can never rely on it.

Flying next to a mountain you can easily be into wind or downwind. Katabatic and anabatic winds flow up and down the mountain and, if the pressure gradient wind is perpendicular to the mountain you would be in either updraughting or downdraughting air depending on whether you are on the windward or lee side of the mountain. You can be into wind or downwind in updraughting or downdraughting air and vice versa. If the pressure gradient wind is parallel to the mountain then you would be predominately into wind or downwind.

As to having no mountains in the UK, I can guarantee that they are big enough and dangerous enough to catch out even the best pilots.

Mountain flying (including mountain weather and mountain winds) is a very complex and demanding subject. I would advise anyone contemplating it to read up on the subject first. If going mountain flying in winds greater than about 10-15kts then you may want to think about getting some advanced instruction in mountain techniques.

Goatwacker: Kudos to you for sharing your experience and glad to hear all ended well.

[Tuned In]

Does IO540 have some sort of obsession with GPS? My comment would have been exactly the opposite - I think he reached for GPS too early, unless he was just turning it on ready to use if the situation was not quickly resolved. It is very easy for someone to get focussed on something with a moving map at the expense of the flight instruments. There are other things that take priority, and other ways of resolving the problem that should be tried before reaching for the GPS to navigate. By the time they have been run through the GPS will have its first fix.

I think I'd quite like to fly with Chilli though.

[Fuji Abound]

I recall a similiar experience a few years back.

Overcast at around 5,000 feet, otherwise clear air, no local thunder storm activity, but maybe a cell around thirty miles to the south.

Level, low ground with a small ridge to the north up to 500 feet. Light wind.

At 4,500 feet I got caught in presumably a micro burst. With the engine at full chat I was getting a 1,000 fpm descent in totally smooth air. Fortunately there was a grass strip I know over my left shoulder, but at 500 feet and still descending, enountered light to moderate turbulence and air rising as quickly.

Never quite understood the events of that day or the circumstances that caused the micro burst. I always wondered at what height the descent would have stopped if I had not passed into the rising air.

I will also remember I thought for some while the problem was with the engine and couldnt understand why in spite of everything appearing normal I was descending at an alarming rate. Of course everything was normal! (at least so far as the engine was concerned).

[bookworm]

I think I saw the 'CAVOK' bit on the forecast, rejoiced and didn't look at much more in any detail. So I also missed the whopping great SIGMET for severe turbulence, didn't I!!!

CAVOK is good at lulling into a false sense of security. I made a flight a few weeks ago where everywhere was reporting CAVOK. When I arrived at my destination, it was still CAVOK. It was also 18 gusting 25 across a runway half as long and half as wide as I was used to, with a cliff at the end for good measure. The approach was ... interesting.

[IO540]

Does IO540 have some sort of obsession with GPS?

Oh for F*CKS sake!
Some people like to fly without GPS, some people like to look out the window, some people like to use a map occasionally. Flying isn't JUST about switching on all the gadgets and following the lines. .

Let's examine the supporting evidence for the above statements, based on what I actually said in this thread...

It should have been ON the whole time, checked for satellite reception before starting the taxi. Do you push start your car, and use the starter motor only when too tired or when parked uphill?

As to those having a go at me over suggesting that a GPS should be switched on if it is being carried at all, I am suprised as some who did should definitely know better. A GPS in the bag, not switched on, is about as much use as a chocolate teapot.

So, I think some people are getting a bit over-excited. Must be the summer weather

[Chilli Monster]

Originally Posted by IO540

It should have been ON the whole time, checked for satellite reception before starting the taxi. Do you push start your car, and use the starter motor only when too tired or when parked uphill?

This was what I was having a go at - why SHOULD it have been switched on. Why can't it be switched off. So the guy felt the need for it later. Fine - though I think getting the aircraft stable and in a situation where you won't impact cumulo granitus first would have been a better idea. You don't have the right to tell them what they should or shouldn't be doing - that's their decision.

You've banged the GPS drum enough - like I said before, give it a break - even the supporters get pi**ed off after a while.

[Saab Dastard]

goatwhacker - great post, thanks for sharing your learning experience! You have definitely emptied your bag of luck a bit, but you have also filled up your bag of experience!

I don't see how a downdraught can force a plane into the ground.

IO, the thing is that descending air can and does descend all the way to the ground. When it hits the ground it "bounces" and spreads outwards. Unfortunately aircraft don't bounce so well!

This can be seen in "pure" vertical downdrafts - microbursts - which have been the cause of several large passenger jets hitting the ground on final approach. So severe is the problem in some states in the US that they have installed systems to warn ATC and aircraft of such microburst activity close to airports. Microbursts are usually associated with storm-cell activity.

Very similar effects can be experienced in the turbulent air on the lee-side of mountains and hills, particularly in the rotor area. You will find that there is frequently - not always - a component of the rotor that actually strikes the ground. A light aircraft caught in such a situation is unlikely to have sufficient power to overcome the downdraft.

Even in situations where the rotor or turbulent air does NOT actually strike the ground, an aircraft may STILL hit the ground due to its inertia - it takes a signifcant time to convert a high rate of descent into a climb, even if the air itself is not descending.

It is exactly the same as if you had dived towards the ground and pulled out too late. BANG!!

I have a background in civil engineering (fluid mechanics) and I also have some experience of flying gliders in ridge-soaring and wave conditions - bottom line is that it really, really is possible to have an aircraft slammed into the ground by downdrafts in mountains.

SD

[QDMQDMQDM]

This accident report shows what happens when you end up in downdraughts on a lee ridge:

http://www.bfu.admin.ch/common/pdf/1730

Even if you don't read German, scroll down to the pictures, which tell the story.

[IO540]

You don't have the right to tell them what they should or shouldn't be doing - that's their decision.

Why post a story (of a near accident) in a public forum if not expecting suggestions?

[jetflite]

Thus leading to why Pilots of aircraft/helicopters approaching mountains from the lee side shall do so at 45degree angle, allowing sufficient time that if a sever down draft is incountered the aircraft can make a turning decent/climb away from the MOUNTAINS, ALWAYS have an escape route.

Originally Posted by IO540
I don't see how a downdraught can force a plane into the ground.

One of the most common forms of accidents are CFIT(controlled flight into terrain) including down drafts and microburst/clear airpockets,
all these play a dangerous part in aviation and are often over looked until you are unfortunate enough to encounter it and if survived it to always be aware of them. I my self experienced a Drop of 1500ft in a twin-engine aircraft to find my self 500ft above terrain and my No.2 engine to surging due to the negative G and engine feeding/fueling issues, Since then i can assure you that you constantly fly with an escape route over mountains!

[goatwhacker]

I will also remember I thought for some while the problem was with the engine and couldnt understand why in spite of everything appearing normal I was descending at an alarming rate. Of course everything was normal! (at least so far as the engine was concerned).

I had the same feeling. Checked full power, checked mixture was fully rich, checked Ts and Ps, checked RPM - all normal for full power, but WTF are we still descending?????

That was I think what really shook me about the whole thing.

[SparkyBoy]

Originally Posted by IO540

What "mountains" were these? There are no mountains in the UK.

The dictionary defines a mountain as that which is ‘higher and steeper than a hill’. It is a landform that extends above the surrounding terrain in a limited area. Mountains usually have steep, sloping sides and sharp or slightly rounded ridges and peaks.
Generally, mountains are landforms that rise above 600 metres. Mountains exist on every continent and even beneath our great oceans.

Below a list of half of the English mountains and I don't have room on the forums for the amount of Scottish mountains (approx 750)

Scafell Pike97834BCentral and Western Fells89,90NY 215072Scafell96434BCentral and Western Fells89,90NY 206064Symonds Knott95934BCentral and Western Fells89,90NY 207067Helvellyn95034CEastern Fells90NY 341151Ill Crag93534BCentral and Western Fells89,90NY 223073Broad Crag93434BCentral and Western Fells89,90NY 218075Skiddaw93134ANorthern Fells89,90NY 260290Helvellyn - Lower Man92534CEastern Fells90NY 337155Great End91034BCentral and Western Fells89,90NY 226084Bowfell90234BCentral and Western Fells89,90NY 244064Great Gable89934BCentral and Western Fells89,90NY 211103Cross Fell89335AThe Northern Pennines91NY 687343Pillar89234BCentral and Western Fells89,90NY 171120Nethermost Pike89134CEastern Fells90NY 343141Catstye Cam89034CEastern Fells90NY 348158Esk Pike88534BCentral and Western Fells89,90NY 236075Raise88334CEastern Fells90NY 342174Fairfield87334CEastern Fells90NY 358117Blencathra86834ANorthern Fells90NY 323277Bowfell North Top86634BCentral and Western Fells89,90NY 245070Skiddaw - Little Man86534ANorthern Fells89,90NY 266278White Side86334CEastern Fells90NY 337166Striding Edge86334CEastern Fells90NY 350149Crinkle Crags - Long Top85934BCentral and Western Fells89,90NY 248048Dollywaggon Pike85834CEastern Fells90NY 345130Great Dodd85734CEastern Fells90NY 342206Grasmoor85234BCentral and Western Fells89,90NY 174203Gategill Fell Top85134ANorthern Fells90NY 318274Great Dun Fell84835AThe Northern Pennines91NY 710321Atkinson Pike84534ANorthern Fells90NY 324282Stybarrow Dodd84334CEastern Fells90NY 343189Little Dun Fell84235AThe Northern Pennines91NY 704330Scoat Fell84134BCentral and Western Fells89NY 159113St Sunday Crag84134CEastern Fells90NY 369134Crag Hill83934BCentral and Western Fells89,90NY 192203Crinkle Crags South Top83434BCentral and Western Fells89,90NY 249045High Street82834CEastern Fells90NY 440110Pillar - Black Crag82834BCentral and Western Fells89NY 166117Red Pike82634BCentral and Western Fells89NY 165106Hart Crag82234CEastern Fells90NY 368112Steeple81934BCentral and Western Fells89NY 157116Shelter Crags81534BCentral and Western Fells89,90NY 249053The Cheviot81533The Scottish Border to the River Tyne74,75NT 909205High Stile80734BCentral and Western Fells89,90NY 170148Lingmell80734BCentral and Western Fells89,90NY 209081The Old Man of Coniston80334DSouthern Cumbria96,97SD 272978High Raise80234CEastern Fells90NY 448134Kirk Fell80234BCentral and Western Fells89,90NY 194104Swirl How80234DSouthern Cumbria89,90NY 272005Green Gable80134BCentral and Western Fells89,90NY 214107Haycock79734BCentral and Western Fells89NY 144107Brim Fell79634DSouthern Cumbria79NY 270985Green Side79534CEastern Fells90NY 352187Knock Fell79435AThe Northern Pennines91NY 721302Dove Crag79234CEastern Fells90NY 374104Rampsgill Head79234CEastern Fells90NY 442127Grisedale Pike79134BCentral and Western Fells89,90NY 198225Mickle Fell78835AThe Northern Pennines91,92NY 804243Kirk Fell East Top78734BCentral and Western Fells89,90NY 199106Allen Crags78534BCentral and Western Fells89,90NY 236085Great Carrs78534DSouthern Cumbria89,90NY 270008Thornthwaite Crag78434CEastern Fells90NY 431100Glaramara78334BCentral and Western Fells89,90NY 246104Kidsty Pike78034CEastern Fells90NY 447126Pillar Rock78034BCentral and Western Fells89,90NY 171123Dow Crag77934DSouthern Cumbria96,97SD 262978Harter Fell77834CEastern Fells90NY 459092Red Screes77634CEastern Fells90NY 396087Glaramara - Looking Steads77534BCentral and Western Fells89,90NY 245101Shelter Crags North Top77534BCentral and Western Fells89,90NY 249057Grey Friar77334DSouthern Cumbria89,90NY 259003Sail77334BCentral and Western Fells89,90NY 198202Wandope77234BCentral and Western Fells89,90NY 188197Hopegill Head77034BCentral and Western Fells89,90NY 185221Meldon Hill76735AThe Northern Pennines91NY 771290Great Rigg76634CEastern Fells90NY 355104Stony Cove Pike76334CEastern Fells90NY 417100Wetherlam76334DSouthern Cumbria89,90NY 288011High Raise76234BCentral and Western Fells89,90NY 280095Ill Bell75734CEastern Fells90NY 436077Hart Side75634CEastern Fells90NY 358197Sand Hill75634BCentral and Western Fells89,90NY 187218Red Pike75534BCentral and Western Fells89NY 160154Dale Head75334BCentral and Western Fells89,90NY 223153Little Fell74835AThe Northern Pennines91NY 781224Burnhope Seat74735AThe Northern Pennines91NY 785375Carl Side74634ANorthern Fells89,90NY 254280Black Sails74534DSouthern Cumbria89,90NY 282007High Crag74434BCentral and Western Fells89,90NY 180140Round How74134BCentral and Western Fells89,90NY 218081Little Stand74034BCentral and Western Fells89,90NY 250034Hobcarton Crag73934BCentral and Western Fells89,90NY 194220Robinson73734BCentral and Western Fells89,90NY 201168Harrison Stickle73634BCentral and Western Fells89,90NY 281073Seat Sandal73634CEastern Fells90NY 343115Whernside73635BThe Central Pennines98SD 738814Combe Head73534BCentral and Western Fells89,90NY 249109Long Side73434ANorthern Fells89,90NY 248284Little Gowder Crag73334BCentral and Western Fells89NY 140109Kentmere Pike73034CEastern Fells90NY 465077Codale Head73034BCentral and Western Fells89,90NY 289090Hindscarth72734BCentral and Western Fells89,90NY 215165Clough Head72634CEastern Fells90NY 333225Ullscarf72634BCentral and Western Fells89,90NY 291121Ingleborough72435BThe Central Pennines98SD 740745Thunacar Knott72334BCentral and Western Fells89,90NY 279080Glaramara South Top72134BCentral and Western Fells89,90NY 242097Froswick72034CEastern Fells90NY 435085Whiteside71934BCentral and Western Fells89,90NY 175221Birkhouse Moor71834CEastern Fells90NY 363159Harwood Common (Redgleam)71835AThe Northern Pennines91NY 795363Great Shunner Fell71635AThe Northern Pennines98SD 848973Brandreth71534BCentral and Western Fells89,90NY 214119Lonscale Fell71534ANorthern Fells89,90NY 285271Hedgehope Hill71433The Scottish Border to the River Tyne80NT 943197Branstree71334CEastern Fells90NY 477100Dead Stones71035AThe Northern Pennines91NY 793399Knott71034ANorthern Fells89,90NY 296329High Seat70935AThe Northern Pennines91,92NY 802012Melmerby Fell70935AThe Northern Pennines91NY 652380Pike of Stickle70934BCentral and Western Fells89,90NY 273073Great Stony Hill70835AThe Northern Pennines91,92NY 823359Wild Boar Fell70835AThe Northern Pennines98SD 758988Whiteside West Top70734BCentral and Western Fells89,90NY 170219Yoke70634CEastern Fells90NY 437067Pike of Blisco70534BCentral and Western Fells89,90NY 271042Great Whernside70435BThe Central Pennines98SE 001739Chapelfell Top70335AThe Northern Pennines91,92NY 875346Ladyside Pike70334BCentral and Western Fells89,90NY 184227Middleboot Knotts70334BCentral and Western Fells89,90NY 213080Bowscale Fell70234ANorthern Fells90NY 333305Buckden Pike70235BThe Central Pennines98SD 960787Cold Pike70134BCentral and Western Fells89,90NY 262035Pavey Ark70034BCentral and Western Fells89,90NY 284079Backstone Edge69935AThe Northern Pennines91NY 725277Gray Crag69934CEastern Fells90NY 428117Caw Fell69734BCentral and Western Fells89NY 131109Grey Knotts69734BCentral and Western Fells89,90NY 217126Rest Dodd69634CEastern Fells90NY 432136Fendrith Hill69635AThe Northern Pennines91,92NY 877333Great Knott69634BCentral and Western Fells89,90NY 260043Archy Styrigg69535AThe Northern Pennines91,92NY 802003Pen-y-ghent69435BThe Central Pennines98SD 838733Seatallan69334BCentral and Western Fells89NY 139083Great Calva69034ANorthern Fells89,90NY 290311Hugh Seat68935AThe Northern Pennines98SD 808991Great Coum68735BThe Central Pennines98SD 700835Round Hill68635AThe Northern Pennines91NY 744361Allen Crags North Top68434BCentral and Western Fells89,90NY 240092Bannerdale Crags68334ANorthern Fells90NY 335290Cold Pike West Top68334BCentral and Western Fells89,90NY 258035Swarth Fell68135AThe Northern Pennines98SD 755966Plover Hill68035BThe Central Pennines98SD 848752Loft Crag68034BCentral and Western Fells89,90NY 277071Baugh Fell - Tarn Rigg Hill67835AThe Northern Pennines98SD 740916The Calf67635AThe Northern Pennines98SD 667970Combe Door Top67634BCentral and Western Fells89,90NY 253108Knoutberry Haw67635AThe Northern Pennines98SD 731919James's Hill (Westernhope Moor)67535AThe Northern Pennines91,92NY 923325Lovely Seat67535AThe Northern Pennines98SD 879950Murton Fell67535AThe Northern Pennines91NY 753246Sheffield Pike67534CEastern Fells90NY 369181Calders67435AThe Northern Pennines98SD 671960Killhope Law67335AThe Northern Pennines86,87NY 819448Branstree East Top67334CEastern Fells90NY 487103Wether Hill67334CEastern Fells90NY 456167Great Knoutberry Hill67235BThe Central Pennines98SD 788871Rogan's Seat

[possel]

Originally Posted by coodem

Did a pre flight, took off by the time I was at 500 feet I saw all the clouds nearing in, next minute I was in the middle of the whole lot. It was as if someone put the duvet over the aircraft. Could not even see the prop in front of me, I was around 1000ft AGL,

I learned that one when doing my PPL. We were going to do some dual circuits and it looked just OK perhaps 800ft when pre-flighting. By the time we got to the end of the runway it had got worse as when I took off the cloudbase was nearer 400 ft. My instructor showed me how to do a low level circuit and we landed. He then said "I expected you to see how bad it was and decide to not take off, but thought I would let you learn for yourself!"

I certainly did - thanks Kev. Always best to learn when you have some experience on board rather than solo!

[wobble2plank]

Love this thread!!!!

Met and turbulence are major killers within the aviation industry and hobby. Be it viz, cloud, turbulence, hail or any other of the bizarre things that mother nature can throw at us.

As to the one about vertical flow can not force and aircraft into the ground, that one is a distinct killer! A fair few years ago I was piloting an 11 ton helo into a small island to pick up a casualty when we were caught by a monster up draught caused by the north atlantic winds striking the rather hilly mountain island (yes they were that strong!). I lowered the collective to reduce the rate of climb but to no avail, I was effectively in autorotation and climbing at 2000 fpm. Luckily it all died down by 2000' and I could sneak back in by going low over the ground. Whats the reason for this story? Reverse the flow, place it at low level and then add in the inertia of a mechanical object travelling toward the ground at 1000fpm plus. This is where air wins and we don't.

Turbulence is an interesting one, especially in mountainous terrain, hence the requirement for greater safety altitude separation. The demarkation line that seperates the smooth flow from the tubulent is no stationary. Rollers exist below and smooth flow above. This line is, however, greatly influenced by what is upwind of the ridge/hill/mountain that you are flying past.

Honesty and a willingness to learn will stand all of us in good stead.

Avoid cumulo granite, read the weather but more important UNDERSTAND IT!

[Tuned In]

IO540

Why, if the pilot does not intend to use the GPS in the normal course of the flight, should it be switched on? Unless the pilot is so underconfidant that they would cancel the flight if it wasn't working then it is an extra, not an essential and they can wait for it to power up!