CFIT

[Bla Bla Bla]

Allot of idea's from allot of people, but when flying in big mountains that you cannot simply out climb in your SEP you spend most of the time checking behind you so you do not get trapped in that sort of rubbish. Keep the back door open at all times and always have an escape route in the mountains. Its simple any good mountain pilot will turn away from that sort of weather way before it becomes an emergency. Its not what you will do once you are in it, its what you will do before you are in it.

I found my time private flying around the South downs of England not as informative as my years commercial flying around the Southern Alps of NZ.

[bjornhall]

And that's what worries me.

Difference between us. I think you've got the whole thing backwards, but I'm not the least bit worried. I care about how I fly, I don't care how you do it.

- seeing ahead: fine if you fly through a gap in mountains or a very short valley, where you can actually see the other side - and, importantly, know there is not another valley hiding there!

Yes. So why are you so upset then? "I only fly through valleys if I can see a way through", remember?

- do a 180: fine, IF valley is wide enough and IF the wx hasn't closed in behind you. Doesn't seem to work too well in practice, though, as by the time most pilots realize they are up the creek - they literally are, and there's not enough space left.

You read too many accident reports. Might be worth recalling that there are no reports written when that method succeeds. It is a rare exception that pilots don't make it out a valley one way or the other, so "most pilots" might be a stretch.

- put the plane down: laughable. This whole idea of 'precautionary landing' only works if you have options. Examples: having a line of CBs across your path and not enough room to divert. Find a little airfield, land, wait. Approaching mountains, find the wx cr*p, cannot outclimb - turn around and land somewhere. 'Putting the plane down' in a mountain valley in a distress situation ? Funnily, these valleys don't tend to have airfields (or any fields, for that matter). Think rocks and bog and trees.

Putting the plane down is always an option. Pilots who disagree to that have one less tool to use to avoid becoming fatalities. It will most likely destroy the plane and it is not unlikely to result in injuries or worse, but it is an option. Lots and lots of accidents would have been avoided if pilots had used it. Difficult decision, yes, but flying isn't always easy!

However, the safe bet is ALWAYS to stay on top of the mountains, above MSA. In aviation, height (above ground) is your friend !

Any sentence with an "always" in it is necessarily mistaken. The list of exceptions is endless; ice, high winds at high altitude, how do you get above MSA, how do you get back down again, what if MSA is higher than you can fly (oxygen etc), and so on and so forth.

I think a safe pilot should know more than one way to fly.

[Stephen Furner]

I seem to recall reading a magazine item a while ago that claimed the Antonov AN2 manual suggested when all else failed the aircraft could be stalled and mushed down to a safe landing. The claim being that in this configuration the aircraft will descend at a slow enough speed for the under carriage to be able to absorb the landing impact energy allowing those on board to walk away unharmed.

In the absence of a ballistic parachute this might be a strategy for bringing a light aircraft safely down to a valley floor where its handling characteristics allow if caught out in IMC. If the aircraft becomes VFR during the decent it could be flown on to a powered landing.

When I stall my C172 it will mush down at about 500ft per min which is roughly 5.7 miles an hour. Intuitively this sounds within the capabilities of the under carriage although I have no data on its performance specification to confirm this. Certainly I suspect there would be a better chance of survival from a vertical 5.7 miles an hour impact than CFIT into a valley wall at the typical cruise speed of 95Knots.

In poor weather there may well be a risk of a turbulence induced wing drop developing into a spin because there will be little or no control authority available to take corrective action to prevent it developing.

This kind of tactic if it works is I think a last hope attempt to manage down the risk of damage in an inevitable contact with the terrain.

[scooter boy]

"Inadvertent" IMC? - what a joke that is.

It is only ever really inadvertent at night and even then you can usually tell you are about to enter cloud if there is any moonlight or ground lighting at all.

Otherwise it is never inadvertent.

Our VFR only bonanza "pilot" will have had significant warning as the cloud filled in and should never have ended up in this situation. Cloud entry is almost never truly inadvertent from day VFR.

I would guess the poor schmuck doing the VT in the back (A) was not a pilot (B) had no idea he was nearly murdered by someone else's horrendous misjudgement. The tone of the piece is almost "beware mountains can sneak up on you" rather than "beware the murderous newbie PPL who wants to show off his new toy to you".

...I hope he learned from it - and after landing I hope he punched the "pilot" as hard as he could and vowed never to fly with him again ...

[englishal]

When I stall my C172 it will mush down at about 500ft per min which is roughly 5.7 miles an hour. Intuitively this sounds within the capabilities of the under carriage although I have no data on its performance specification to confirm this. Certainly I suspect there would be a better chance of survival from a vertical 5.7 miles an hour impact than CFIT into a valley wall at the typical cruise speed of 95Knots.

Sounds a bit low to me. I think I calculated that our Rallye had a vertical descent rate of about 15 mph in a full stall, and that is nicknamed the "tin parachute". Still 15mph is survivable and there is a story going around of someone running out of fuel at night in a Rallye and doing just that....

Don't forget though that when stalled you still have forward velocity, so could be travelling 30mph+ forward when you touch down.

I wouldn't fly around high mountains with "mountain obscuration" at the tops, when the MSA was > 9-10,000'. If the IMC was low down, say topping at 6k then I'd climb on top, or land...

[IO540]

When I stall my C172 it will mush down at about 500ft per min which is roughly 5.7 miles an hour. Intuitively this sounds within the capabilities of the under carriage

The velocity, and thus the energy which needs to be dissipated, is the vector sum of the forward velocity (say 50kt) and the vertical velocity (say 5kt) i.e. slightly over 50kt.

In fact one could make the vertical velocity zero - by pulling up a bit at the point of impact. But that still leaves the whole forward velocity to dump.

If you do this at an airport, it's called a landing

The other thing is that few GA planes will be long term stable in roll, especially if there are significant roll disturbances. So, loss of control in IMC will rapidly result in the "spiral of death", unless the pilot does something reasonably sensible (like keeping wings level).

I gather some flexwing microlights are stable in roll and upon IMC entry one could just take one's hands off and the thing will descend with wings level, but GA spamcans won't do that.

I agree with SB there is probably no such thing as inadvertent IMC entry, but psychology is a big factor in this, and people do press on into poor vis which then becomes poorer vis, etc. Nobody likes the idea of turning back.

[JP1]

To fly like that is sheer folly.

To put it on YouTube is almost as stupid....

If you read the comments below the video, the Youtube poster and the guy with the video camera have made comments.

They are simply (3) friends of the guy having a ride in the L-39 and went in the Bonaza to film their friend, non of them are pilots. I assume they did not know the pilot of the Bonaza either.

The video has been posted to clearly show the idiotic behaviour of the pilot that nearly killed them. They have handed the video onto the FAA to be investigated.

[IO540]

This rather older one is pretty amazing too. Thread here.

I recall when the pilot first wrote about it in the Socata TB user group, c. 2006. From there, it "escaped" into the wild somehow...

[Stephen Furner]

Good point about the forward velocity.

Treating this as a simple right angled triangle in a straightforward parallelogram of forces. Square of the vector for the decent path of the aircraft will be the forward vector (stall speed) squared plus the vertical decent rate squared. Which is (50 x 50) + (6 x 6) = 2500 + 36 = Therefore the speed of impact at touch down is SQRT2536 = 50 mph.

Clearly it’s the forward velocity that is the dominant factor no matter how slow the decent rate as result of mushing down in a stalled configuration. The more the forward velocity can be reduced the lower the impact speed. Even if were possible to get the forward velocity down to the 6 mph of the decent rate the impact speed will still be around 8 mph.

It looks like the key to making this manoeuvre work is to reduce the forward speed as much as possible by increasing the depth of the stall, turning into wind or maintaining enough control authority to flare before touchdown.

In a confined space of a valley turning into wind isn’t an option so there may be well be additional speed if there is a tailwind.

[Piper.Classique]

Clearly it’s the forward velocity that is the dominant factor no matter how slow the decent rate as result of mushing down in a stalled configuration. The more the forward velocity can be reduced the lower the impact speed. Even if were possible to get the forward velocity down to the 6 mph of the decent rate the impact speed will still be around 8 mph.

I'm not sure you have the whole picture here. The aircraft's crashworthiness may well depend on what hits first, and a high rate of descent with low forward velocity might not be the best configuration for survivability. If you are genuinely stalled there is of course no possiblity of a flare. Mushing down in a stalled condition the rate of descent is quite high. It might be better to wipe off the undercarriage with some forward movement and a lower rate of descent. Any engineers here who could clarify? Any pilots here who actually do mountain flying in a serious way? Or are we all just guessing?
So far I see no-one suggesting a parachute for the pilot. Of course, I wear one when flying a glider, in France it is actually a requirement. Problem is, when we are scraping along a ridge at 8000 feet amsl we often only have about 50 feet clearance at the wing tip, and not a lot more underneath. We do take _VERY_ great care to stay VMC. Which is probably the way to go with less than two engines anyway

[englishal]

Any engineers here who could clarify? Any pilots here who actually do mountain flying in a serious way? Or are we all just guessing?

High mountains and IMC don't mix unless you have 4 turbofans, and 400 seats on-board and are 30,000' above

I think the best option is to remain flying until touch down. Physics says that as long as you don't decelerate too quickly (i.e. hit a tree) then you can probably walk away. I seem to remember a Indy Car driver experiencing 130G in an impact and he walked away, a bit bruised but ok. You need a relatively short distance to decelerate to pull less than 9G. 25m landing "roll" at 40 kts will pull 8g if my high school physics is correct -easily survivable - some people do this for fun !

[IO540]

The basic point is that no matter what you do, you can't fly slower than Vs.

The ground contact will always be made at a speed around that figure, at best.

I once read, from a famous aerobatic champion, that upon entry into IMC one could enter a flat spin and spin all the way down through the cloud. Presumably he would have intended to recover below the cloud... otherwise it's true his forward speed would have been low but what about the vertical speed? Maybe that is quite low as well - not something I want to try in the TB20

In general, the term "mountain flying" is intended to mean flying in the canyons. Often this is done with the tops shrouded in cloud. This is done a lot in the Alps, where you have huge valleys with flat bottoms, and often the cloudbase is thousands of feet above the bottoms. The pilots that do this are trained to know the area well, and to not enter valleys which are a tight dead end, etc.

I would not do any of that - I fly straight across the top at FL160-190.

[Wrong Stuff]

If you can simply stall an aircraft to a safe crash landing then Cirrus have wasted an awful lot of effort attaching effin great rocket-propelled parachutes to their aircraft and using impact absorbing undercarriages and seats to cushion the crash. I bet they wish they'd just tried stalling it in first.

[englishal]

The ground contact will always be made at a speed around that figure, at best.

unless you have a 40 kt headwind

[gasax]

I have a reasonable level of experience of flying in mountains (well high ground!) in IMC. The point is at what height does the IMC start?

It is entirely possible to fly across high ground VMC below a solid ceiling. It needs to be high enough and you need to really, really know where you are. But it is very commonly carried out.

The 'received wisdom' seems to be if you enter IMC you climb and get above safety altitude. Well nice idea, but reallt difficult to achieve.

If you end up in a 'dead end', the chances of outclimbing the terrain are pretty poor. Most light singles struggle to get 1000fpm - as a gradient it might suit railways, to outclimb the average hill it is completely inadequate.

If you run out of VFR conditions you have a very short time to decide whether you throw the dice and hope you are flying up the valley whilst you climb or you force land.

A forced landing up a hill can result in a ground speed of virutally nothing. fly up the slope, hold off and then land - the ground spped if carried out well is virtually nothing

[gasax]

I have a reasonable level of experience of flying in mountains (well high ground!) in IMC. The point is at what height does the IMC start?

It is entirely possible to fly across high ground VMC below a solid ceiling. It needs to be high enough and you need to really, really know where you are. But it is very commonly carried out.

The 'received wisdom' seems to be if you enter IMC you climb and get above safety altitude. Well nice idea, but reallt difficult to achieve.

If you end up in a 'dead end', the chances of outclimbing the terrain are pretty poor. Most light singles struggle to get 1000fpm - as a gradient it might suit railways, to outclimb the average hill it is completely inadequate.

If you run out of VFR conditions you have a very short time to decide whether you throw the dice and hope you are flying up the valley whilst you climb or you force land.

A forced landing up a hill can result in a ground speed of virtually nothing. fly up the slope, hold off and then land - the ground seped if carried out well is virtually nothing.

You do need practice at landing on steep gradients - but once you have that you will neverr be able to understand why airfields are on level ground. The gradient makes an enourmous difference - you can literally park on a hillside. Getting the aircraft will need a helicopter but you will step out and walk to a phone (so long as you have sensible footwear and clothing!).

It would be great to simly fly over the top - but my aircraft does not have the ceiling or icing protection to allow that. I can fly through the valleys - it needs care and occasionally needs the odd U turn. Going IMC, when a precise heading is necessary - probalby with a turn, is all that stops contact with cumulo-granite is not a smart move, I'll land!

[IO540]

Getting the aircraft will need a helicopter

Is this actually ever done? I don't know... I would expect the thing to be written off if it cannot be retrieved with a tractor etc.

[Sam Rutherford]

If I ever find myself inadvertent IMC in a valley, in the mountains, I'm not sure that aircraft retrieval post crash is going to be high on my list of concerns!

Safe flights.

Sam.

[mary meagher]

The only thing more dangerous than showing off is amateur filming of another aircraft in flight.

This was the root cause of the idiocy. All their attention was on filming the other aircraft. Like towing a water skier with everybody looking astern.....

[gasax]

Actually where I live aircraft are either recoveed by helicopter or stripped by 'walkers' and others.

The point is that your priorities should be the fragile tissue and flesh. Sometimes it is difficult to get to the nub of it but - a low speed forced landing or even crash if carried out under marginally forced conditions is a hell or a sight better than smashing into granite at 100 plus knots