CFIT

[Maoraigh1]

Never inadvertant IMC

A C177 was caught in downdraft which it could not outclimb, flying south from Inverness in the early 90s. It was VMC on top, 7500'? but was pulled down, into the 6000'? cloud, and below the summit levels. After sighting rock off the wingtip, it hit an updraft, and was carried back up. PPL/IMC and CPL/IR?/Instructor cancelled flight and returned very shaken to base. No accident so no AAIB report. There was a description in the then HAC Newsletter.
Cloud can form suddenly when a packet of moister air rises as it meets rising ground, giving an unwary pilot inadvertant IMC.

[IO540]

For him to get pulled down by 1500ft you'd be looking at a wind speed of at least 15-20kt (-500fpm assumed).

Not a lot.

[gasax]

In my 'back yard' there was a G115 which went into a loch on a windy day - weather was IMC above the tops, below them very active. so active that even ground effect did not seem to say them (instructor and student).

Less of an IMC issue - but when the wind is blowing the ceiling can be very variable. The wae effect can result in a classic 'box canyon' situation - where it is either a 180 degree turn or a froced landing.

But the critical aspectg is than you have seconds to decide to keep flying or force land. And generally we do not force land.....

[Stephen Furner]

I checked the stalling and mushing down this afternoon to make sure I had not been over optimistic about the decent rate. This was with a French manufactured Cessna 172H.

Heading into the prevailing wind with the stall warner at full voice and an indicated airspeed showing 40 Knots over several runs the aircraft mushed down at between 500 and 600 feet per minute.

When decending in this configuration the aircraft was not directionally very stable. If this was attempted in a narrow valley I believe there is a good possibility of drifting into the valley sides since directional control was minimal.

[IO540]

Yes, at such low speeds the controls don't work well.

And a level turn increases the wing loading and increases the stall speed, so it is extra risky.

But, the faster you go the greater the minimum achievable turn radius, so if having to do a tight 180 it is better to slow down.

[bjornhall]

Totally impractical suggestion: With a hammerhead you could make a 180 degree turn no matter how narrow the valley is...

Told you it was impractical!

[IO540]

You could also make a very tight turn if you had room below you, to unload the wings during the turn.

Needs an understanding of how the stall speed depends on wing loading.

It's a good tactic for flying tight turns onto final (scares the passengers though ).

[mm_flynn]

Originally Posted by Stephen Furner

I checked the stalling and mushing down this afternoon to make sure I had not been over optimistic about the decent rate. This was with a French manufactured Cessna 172H.

Heading into the prevailing wind with the stall warner at full voice and an indicated airspeed showing 40 Knots over several runs the aircraft mushed down at between 500 and 600 feet per minute.

I suspect this was a power on stall/mush scenario. If you add another 20% to your forward speed you now have lots of control and minimal vertical speed (so the net total deceleration is about the same - but in a direction your body can stand much better). Also, flying rather than mushing you have a much better chance of arriving wings level and skidding over the rocks rather than catching a wing and cartwheeling.

Clearly you want to land along the surface going slow, rather than into a cliff going fast ... but 'stalling it in' seems to always be a worse answer than flying it in.


Also, when you hit the ground you want the engine at low power/off so when the prop hits something it doesn't rip the engine out and then chop through the cockpit before it stops running. This means there is a last second chop of the power (and consequent drop like a rock) necessary when stalling it in.

In terms of landing in a short distance, unless I have made a mistake, an approach at 60 knots is about 30m/s and with a 5g average deceleration, that would take about 30 feet to crash in (about 1 airplane length!). Well achievable if slidding up a hill.

[Runaway Gun]

I'm quite shocked at this thought of stalling the aircraft into an upwind hill.

And even if you did impact the hill at only 40 or 50kts (hopefully wings level) and survive, what then? Every American movie that has a car chase concludes with the Mustang plunging off the side of the cliff for at least about 800feet before it burts into flame.

Best idea is to utilise less Superhero Biggles skills, and decide earlier to turn around before you reach such a limiting position.

And before that, fly up close to one valley wall, ensuring that you always have turning room available to get out. Better yet, do a course in mountain flying.

[BackPacker]

Totally impractical suggestion: With a hammerhead you could make a 180 degree turn no matter how narrow the valley is...

A hammerhead (or stall turn as it's known here) still requires approximately two wingspans. Whereas a half cuban eight or an immelman (or something inbetween those two) requires only one. Theoretically.

Yeah, I know. Impractical anyway. Better use your superior judgement to avoid needing to use your superior skill and all that.

[dont overfil]

C172 pitot has a large position error at low speeds.
DO.

[M609]

For some reason it looks like people well versed in mountain flying are the ones that chicken out first turing back/staying on the ground etc IMHO.

I´ve seen people from far away set off VFR in cloud capped valleys in alpine terrain, in condtions when local pilots that know the area well would stay on the couch at home! Some also set off after having been warned by said couch wearing pilots that conditions might not be suitable for flight.

Some only made it after a certain amount of help from ATC after going IMC and climbing to continue IFR. (Why not IFR to begin with? I guess the 0-isotherm below MSA was a factor)

I would not like to be a passenger on a C-182 doing a climb from abborted VFR on the 100ft valley floor to get above the 5000ft peaks in IMC. Hope they had a good GPS with terrain info to assist on the way up!

[172driver]

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

On that we can agree - and also how NOT to fly

[gasax]

The whole issue with flying in mountains is that conditions can be changeable - very changeable.

It is by not means unusual to find the 'ceiling' is highly variable and what was 'fat and happy' one moment becomes very difficult the next.

I have never had to force land up a hill - but I know how to (from practicing on a very steep runway) and if the options were an aerobatic manoeurve or a force landing it would be an interesting decision.

However we have real evidence of aircraft in this area successfully forced landing with no injuries, simply by pulling up when the 'pilot' spotted cumulo-granite.

Never flying is a very good way of avoiding these hazards - sizeable detours is my preferred tactic, but forced landings do work.

As for quoting movies for the outcome of any course of action?? Strangely most of these vehicles usually catch fire before they hit anything. Scouting for locations with a clear drop and convenient camera locations (and clearing up afterward) costs the film production companies a fortune - no wonder they try and spice things up a bit!

[M609]

It is by not means unusual to find the 'ceiling' is highly variable and what was 'fat and happy' one moment becomes very difficult the next.

Indeed, and such knowledge is why seasoned mountain flyers tend to add a little safety margin VX wise.

9999 -RA BKN025 Q1013 TEMPO 7000 RA

That's quite OK for VFR in the flatlands, not so much in the mountains IMHO

One should also consider the fact that you loose the horizon when flying in alpine terrain capped with clouds, and that has caused some disorientation for pilots in the past.

[172driver]

For some reason it looks like people well versed in mountain flying are the ones that chicken out first turing back/staying on the ground etc IMHO.

Indeed, and here's why:

The whole issue with flying in mountains is that conditions can be changeable - very changeable.

[IO540]

9999 -RA BKN025 Q1013 TEMPO 7000 RA

That's quite OK for VFR in the flatlands, not so much in the mountains IMHO

especially as those conditions are probably a warm front which will have tops ~ FL250 so no way to reach VMC above.

I keep meaning to fly to Trondheim, but most days can't even see Norway on the MSLP chart, under the collection of fronts And if it looks OK, finding clear weather a day or two later is much harder.

On clear days the views must be stunning but I'd imagine one gets only a small # of opportunities during the year.

I am a great believer in flying straight over the top of mountains. FL180 takes one ~ 7000ft above the main bit of the Alps and that should be OK with winds of about 30kt. The other day I flew over the middle bit of the Pyrenees at FL140 and about 5000ft over most of the terrain and while the wind was 35kt there was practically zero turbulence (I was quite suprised).

[Piper_Driver]

A hammerhead (or stall turn as it's known here) still requires approximately two wingspans. Whereas a half cuban eight or an immelman (or something inbetween those two) requires only one. Theoretically.

Yeah, I know. Impractical anyway. Better use your superior judgement to avoid needing to use your superior skill and all that.

I heard a story from an well known Vietnam war ace who was flying safety pilot for a cross country voyage with an underage kid (one of those publicity stunts done several years ago before one kid got herself killed). He had to use an immelman to extract his charge after she flew her 152 into a box canyon. It worked, but only because of his superior flying skills - he headed the top gun school at one time in his career. I wouldn't recommend trying this one at home. BTW - he told me that flying with the kid was the dumbest thing he'd ever done in his flying career.

[Pace]

We are missing the point. The thread talks about inadvertant entry into IMC. Okay as one poster said "how can you inadvertantly enter IMC in daylight" well you could be in the cockpit head down writing only to look up and only see white! But maybe unwillingly is a better description deciding to take to the clouds and climb. The lesser of two evils?

But this thread is about being in cloud not under it.

In that situation you cannot just land unsure whether you are descending into cumulus granitus.

You may climb straight ahead if you are pretty damn sure you are flying up a valley. I still hold that in cloud surrounded by hills your best option is to climb in a spiral trying to stay in one place. Even throw the book away and steepen the bank to keep the radius tighter its not that difficult for a competant IR pilot.

There maybe hill slopes either side but remember they are slopes so the higher you go the wider the gap to the hills.

This is a desperate solution to a desperate situation and minimises your chance of hitting terrain it doesnt eliminate it.
If anyone has a better option for IN CLOUD I would love to know what????

And yes you do have to be good on intrument flying and have good situational awareness.

Pace

[Maoraigh1]

Spiral climb

With the surface of the lochs calm and reflecting, I hit moderate turbulence at the east end of Loch Sheil on Monday. There was a strong updraft at one point at the side of Loch Affric. I'm not an instrument pilot, but suggest those considering the spiral climb try it under the hood, with a safety pilot, at a safe altitude, in turbulence. Especially if using steeper than usual turns. (A GPS will enable you to download your track, and see if you kept clear of a virtual hill)
Winds in the hills are unpredictable, and it won't take much to put you into a ridge. Turbulence is usually present somewhere. Often enough to make me (VFR) restrict speed and manoevering.
Staying out of cloud, unless you are at safety altitude, is essential.