How to avoid CFIT

[scifi]

Hi All, I have often wondered what would be the quickest way to avoid an imminent CFIT, if all of a sudden a very large version of The White Cliffs of Dover comes into view. I have visited crash sites in the Berwyns, where WW2 aircraft have hit the mountains. Flying into a dead end valley is a known hazard.

When flying Indoor Models at Broughton, my favourite manoeuvre was to head for the wall, then at the last moment pull up and do a Rudder Stall Turn, to reverse direction. I could get very close to the wall that way, such that a highly banked turn would not have worked. I think that method only works because of adequate speed, and high G capability of models. So maybe it doesn't scale up to the full size aircraft.
.

[Maoraigh1]

Would a tightly banked descending turn have worked with your model?
Most CFIT is in IMC, and you wouldn't be looking out the window, or aware of how far you are from other "walls".
In minimum VMC, at GA light aircraft speeds, you should have time to turn.
VMC CFIT is sometimes linked to downdrafts and turbulence. No precise manoeuvres will be possible in these conditions.

[cavuman1]

My instructor called that evasive maneuver a "Box Canyon Turn". Bank 90 degrees while pulling control yoke to stomach and praying earnestly to one's Maker! A fairly high-G aerobatic exercise, but our trusty 152 held together without complaint nor rippled sheet metal. It did take several hours for my internal organs to return to their normal positions after a half-hour of practice....

- Ed :ok:

[scifi]

Hi Maoraigh, Thanks for the reply. I think it is a bit of an energy management scenario, and the climb part is to reduce the speed and make any turn have less of a radius.
I think at cruise speed you would be below the Loop entry speed, so a half loop to roll-off at the top ( Immelman.) would be out of the question.
Maybe a pull up into a half Lazy-Eight, would give a tight turn around. I suppose it all depends upon your airplane type and your initial speed.
.

[Maoraigh1]

An emergency landing before you get trapped seems to be a good procedure.See the AAIB links below. Manoeuvering in severe turbulence AND downdraft will not be in any way precise, and may overstress the airframe.

http://www.aaib.gov.uk/publications/bulletins/march_1989/piper_pa_28_140__g_avwg.cfm
http://www.aaib.gov.uk/publications/bulletins/august_2005/cessna_150m__n8174v.cfm
http://www.aaib.gov.uk/publications/bulletins/september_1995/cessna_172n_skyhawk__g_bmvj.cfm
http://www.aaib.gov.uk/publications/bulletins/september_1988/cessna_f150h__g_awly.cfm
http://www.aaib.gov.uk/publications/bulletins/september_1994/cessna_152__g_bilr.cfm
http://www.aaib.gov.uk/cms_resources/dft_avsafety_pdf_501881.pdf
http://www.aaib.gov.uk/publications/bulletins/august_1991/cessna_182q__g_bmpo.cfm

[Fl1ingfrog]

I'm very concerned about where this thread is leading. There is no manoeuvre that will ensure terrain avoidance as described and to believe that there is is dangerous fantasie. Even if any terrain was to be avoided with an extreme manoeuvre, a loss of spacial awareness and control is sure to follow.

The only way to avoid terrain with certainty is to avoid it with a wide berth or by flying above it at a minimum safe altitude, whatever the flight conditions.

[pilotmike]

I'm just wondering - if I'm hammering down the motorway at 100mph in thick fog, and I suddenly want to avoid the stationary cars just ahead, am I best to try a handbrake turn, use cadence braking and prayer, or to steer violently towards the crash barrier, then try to catch the tail as it slides out by flooring the throttle and powering away? Or is this just a totally idiotic sort of 'Jet Blast' scifi nonsense idea?

I have tried it with my little RC toy car I Broughton ebuygum, and flicking it left works better than right, but I was wondering if it scales up to real cars. Can anyone tell me which I should try next time I'm unlucky enough to be caught doing a ton up in thick fog and everyone else has slowed right down in front?

Just askin'! Only sensible answers please...:ugh:

[Pilot DAR]

I'm very concerned about where this thread is leading. There is no manoeuvre that will ensure terrain avoidance as described and to believe that there is is dangerous fantasie. Even if any terrain was to be avoided with an extreme manoeuvre, a loss of spacial awareness and control is sure to follow.

The only way to avoid terrain with certainty is to avoid it with a wide berth or by flying above it at a minimum safe altitude, whatever the flight conditions.

This, all of it.

[scifi]

Thanks for those reports Maoraigh, it sort of brings it home to you when one of the aircraft, BILR, was one of the first 152s I flew , when it was based at Sleap.

It seems that the downdraft situations play a big part in those accidents, not a factor I had to worry about when flying the models in the old De-Havilland Staff Dining Hall..!

[Chuck Glider]

Maoraigh has a lot of experience in flying around lumpy terrain and I have a little too, but I recall one flight North over the Grampians when the owner's voice from the rear seat of the Cub asked "why are we descending?" My reply, "because we can't outclimb the sink!"

He and I both knew one who died, along with his passenger, on a mountainside in poor weather probably due to downdraft on the lee side.

[onionabroad]

I would imagine the vast majority of CFIT is when the pilot cannot see the terrain... hence it's "controlled flight"... even in the model example, you have the luxury of being able to see the wall..

How to avoid CFIT? Avoid the situation that causes it... if vfr to imc, then turn arround. if ifr in imc, plan well.

If there's heavy fog on the motorway, do we still drive normally because we know how to do an emergency stop, or do we put a fog light on and slow down to avoid having to even need an emergency manoeuvre ?

[Romeo Tango]

I'm very concerned about where this thread is leading. There is no manoeuvre that will ensure terrain avoidance as described and to believe that there is is dangerous fantasie. Even if any terrain was to be avoided with an extreme manoeuvre, a loss of spacial awareness and control is sure to follow.

The only way to avoid terrain with certainty is to avoid it with a wide berth or by flying above it at a minimum safe altitude, whatever the flight conditions.

It's all very well saying "I would not have started from here". IMHO it's worth the discussion. I would say that it depends on the information you have and what you can see, a violent turn or climb is probably worth a try.

[Dan Dare]

If good planning doesn’t deliver you from CFIT you could consider departing from controlled flight thus making CFIT impossible.

[Maoraigh1]

"The only way to avoid terrain with certainty is to avoid it with a wide berth or by flying above it at a minimum safe altitude, whatever the flight conditions."
Flying at minimum safe altitude will not allow you to predict the downdrafts. Several accident reports show that. Few, if any, light aircraft can maintain altitude if unable to get out of the downdraft.
About 27 years ago a C177 was dragged down from a safe altitude above cloud, into the Cairngorms. They recognised the corrie they came out of cloud in. Before hitting the headwall they hit an updraft and were thrust back up clear of cloud. No damage so no AAIB report. Two very shaken guys turned back to Inverness. The wind forecast was OK when they took off.

Giving terrains a wide berth certainly works. But not everyone lives in flatlands.

[TelsBoy]

Maoraigh seems to fly in the same area I do, and I am familiar with the challenges of doing so. Bottom line is, if you know what you're doing, its perfectly safe. If you don't... you are just inviting trouble on yourself.

How to avoid CFIT is simple... don't go grubbing about in marginal Wx especially near terrain, always have a plan B, C or D if the Wx turns for the worse, be aware and get educated on how to fly in and around mountainous terrain (pay attention to the forecast... where's the wind coming from and how strong is it, cloudbase, freezing level etc... check the terrain on your chart for your route, how will the wind interact with this? Wind stronger than 25Kt at mountain tops can cause problems if you are flying nearby. Etc.), and FFS don't fly for the sake of it! If things look iffy go another day.

Fly safe everyone.

[pulse1]

I have very little experience of flying in mountainous areas and, when I have, I have always kept above MSA. However, doing some float plane training in Scotland I could see how one could become trapped in the "wrong" blind valley in VMC but finding the best climb rate is insufficient to clear the end of the valley. One would already be using best climb speed which would leave no spare energy for fancy maneuvering. If there is no room for a 180, the only option is to find the best ground to land on. I've done this sort of thing frequently on FS in places like British Columbia. FS gives you the extra option of instantly changing aircraft to one with a better ROC.:O

[Pilot DAR]

The scenario of blundering into a tight valley or other confined location in VMC (implying that you you had awareness of your proximity to the ground the whole time) is different from CFIT. CFIT suggests that you are flying in "cruise" flight, and for whatever reason, the ground suddenly surprises you (you didn't see it coming).

If you want to prevent a CFIT, either fly in sight of the ground, or fly IFR above minimum altitudes.

If you've blundered into a tight valley or similar, you did not think about you entered. If you're doing that at cruise speed, even dumber. If you are flying in terrain, and sudden or aggressive maneuvering may be required, fly more slowly, so you're slower than Va, and flap speed. This will increase your options for maneuvering. But hard maneuvering also greatly increases your risk of a stall spin, particularly if you pull G to do it.

I have trained many pilots to fly a canyon turn, usually on floats. Different aircraft fly canyon turns differently, so there is no one size fits all maneuver for this situation. But a key element is to avoid very sudden maneuvering, keeping things smooth, though unusual attitudes may be flown.

I don't deny that pilots get themselves caught in "terrain", and are unable to prevent crashing into it, but if they saw it, and maneuvered to avoid, it was not a CFIT.

[ShyTorque]

the quickest way to avoid an imminent CFIT

Suddenly confronted with "dead end" terrain?

Two phrases come to mind:

1) A superior pilot is one who uses superior judgement to avoid having to use superior skills.

2) Proper prior planning prevents p!$$ poor performance.

[scifi]

There is a thread ongoing in Rumours and News about an airplane that was vectored by LAX ATC the wrong way, putting them towards Mount Wilson. If this was to ever happen in say a Norwegian Fjord, that would be another example of what could go wrong.

Obviously a heavy aircraft will not be able to out-manoeuvre a smaller GA aircraft, so the escape manoeuvres will need to be different. If the GPWS is triggered it will always offer the instruction.. 'Pull Up, Pull Up.', but that assumes that you have some excess energy available.

[Jhieminga]

Scifi, you started this thread by presenting two possible escape manouvres, based on your experience with model aircraft. Please keep in mind that the power loading for a normal GA type aeroplane is vastly different from what you see with a model. Because of this, the available authority from, for example, the rudder is vastly different. And that's before we get into the available margins in the structure with regard to G-loading. All this will be worse if your trusty Cessna or Piper is loaded with a full set of adults and a bit of baggage. From straight and level flight at 100kt, you will be able to apply a fair bit of bank and pull the yoke into your gut, but that is the absolute limit of what I would attempt were I to be faced with a situation as you describe. The next thing I would notice would be the ASI needle heading towards the minimum value on the scale.

I concur with ShyTorque, keep those two phrases in mind at all times, thinking at least one problem ahead. I've been fortunate to have done most of my flying over a very flat landscape, and because of this I have absolutely no plans to venture into more rugged landscapes without a serious bit of preparation. I know that I'm not equipped for that kind of flying, so I either stay away from it or will take someone along who does know the gotchas.

[Maoraigh1]

https://www.caa.govt.nz/assets/legacy/pilots/Flight_Examiner_Ground_Course.ppt
Is this of any interest? There used to be a pdf which I thought more useful but I couldn't find it.
"I've been fortunate to have done most of my flying over a very flat landscape,"
I'd say unfortunate if you're flying for pleasure.:)

[megan]

Discussion here

https://www.pprune.org/flying-instructors-examiners/358312-max-rate-turn-vs-min-radius-turn-3.html

Answer explained. Minimum radius is referred to as "corner speed".

http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/8_Maneuvering.pdf

[Pilot DAR]

Interesting article Megan. Though I completely accept what it says, it's probably beyond the scope of GA flying in a number of places. Keeping to the "private flying" aspect of things, factors such a G loss of consciousness during maneuvering are unlikely, particularly for the flying pilot. If one were to maneuver a normal category GA airplane to the point of Gloc for the pilot, structural damage and loss of control are certain. It's not a CFIT anymore, it's a loss of control - which can happen, but the factors are different. the article and discussion are very worthwhile, though not really relevant to CFIT prevention.

CFIT is prevented by awareness of proximity to terrain - nothing else.

Collision avoidance, in the most extreme last minute case, might be prevented by abrupt maneuvering. But, honestly, if it's come to that point, you're more likely to lose the control you'd like to maintain, by the abrupt maneuvering. It takes a lot of skill to instantly detect the need for abrupt maneuvering, and execute it without exceedance. It'd be easier to apply a fraction of that skill to not needing to do it in the first place.

In the case of close quarters maneuvering, gentle is better. Only as abrupt as is required. And, presuming you're suddenly trying to avoid an obstacle, you want to be really practiced deliberately flying close to things (a challenging skill). If you've errantly got yourself in that tight, use less abrupt maneuvering to not hit the thing, rather than more abrupt maneuvering to give it a wider clearance. There's no point in maneuvering too abruptly and inducing a stall or loss of control to miss it by a mile, when you could have maintained control well, and missed it by enough.

I trained in a particular mountain area in British Columbia (they know mountains there) flying helicopters. I was mentored into a particularly confined looking dead end canyon. (As I measure it on Google earth, it is a mile deep from entry point to the back canyon wall, and 0.8 miles round, 350 feet below the rim, and 400 feet above the descending floor). For a fixed wing pilot like me, that's really tight - but I was being trained in a helicopter, so flying into places like this was more "normal". I worked in this canyon during several training exercises, and got somewhat used to it. (I really never get used to flying toward something I know that I must turn away from, 'cause I cannot out climb it). Anyway, years later, I was est flying a modified deHavilland Beaver amphibian. The very experienced pilot with whom I was flying entered this same canyon - I was terrified! He was calm as normal. I was still terrified!! He gracefully flew around inside this canyon, and back out the way we flew in ('cause there was no other choice!). Then he flipped the control to my side and said "you do it". My slightly subsided terror returned!!! But I did, The trick was to not get phased by it. I flew the wingtip a hundred feet or so off the trees all the way around, in a very gentle (anything but abrupt) turn, and it was fine. I practiced a few more times, and got more relaxed. When I late expressed my fear of doing that, the mentor pilot validated my sense of self preservation, in not doing that kind of thing unsupervised. Then he went on to tell me that that canyon was where he trained water bomber pilots, in much larger (S2F) twin engined water bombers to enter, and not only turn back out, but water bomb down the middle as they exited. So flying the Beaver a lazy circle around there was easy by comparison. I've flown in that area since, but never flown in that canyon again, though possible, and I have proven it to myself, it is still not worth the risk.

But, that was not a CFIT risk, I was well aware of where the terrain was!

[megan]

If one were to maneuver a normal category GA airplane to the point of Gloc for the pilotDAR, I think you are focussing on the wrong message. The lesson the paper I was hoping would give was that flying at Va and turning/banking to point of stall burble would give you 3.8 "g" (normal category limit) and the minimum radius turn, and no ability to overstress the aircraft. No one is going to get G-loc there. It gives you the minimum radius turn, though there are other considerations to be taken into account eg a GA aircraft is highly probable to be power limited, so you would need some altitude (descent) to make up for the lack of power.

From "Aerodynamics for Naval Aviators"The aerodynamic limit describes the minimum turn radius available to the airplane when operated at CLmax. When the airplane is at the stall speed in level flight, all the lift is necessary to sustain the aircraft in flight and none is available to produce a steady turn. Hence, the turn radius at the stall speed is infinite. As speed is increased above the stall speed, the airplane at CLmax is able to develop lift greater than weight and produce a finite turn radius. For example, at a speed twice the stall speed,
the airplane at CLmax is able to develop a load factor of four and utilize a bank angle of 75.5° (cos 75.5°=O.25). Continued increase in speed increases the load factor and bank angle which is available aerodynamically but, because of the increase in velocity and the basic effect on turn radius, the turn radius approaches an absolute minimum value. When CLmax is unaffected by velocity, the aerodynamic minimum turn radius approaches this absolute value which is a function of CLmax, W/S, and AoA. Actually, the one common denominator of aerodynamic turning performance is the wing level stall speed.

The aerodynamic limit of turn radius requires that the increased velocity be utilized to produce increasing load factors and greater angles of bank. Obviously, very high speeds will require very high load factors and the absolute aerodynamic minimum turn radius will require an infinite load factor. Increasing speed above the stall speed will eventually produce the limit load factor and continued increase in speed above this point will require that load factor and bank angle be limited to prevent structural damage. When the load factor and bank angle are held constant at the structural limit, the turn radius varies as the square of the velocity and increases rapidly above the aerodynamic limit. The intersection of the aerodynamic limit and structural limit lines is the “maneuver speed." The maneuver speed is the minimum speed necessary to develop aerodynamically the limit load factor and it produces the minimum turn radius within aerodynamic and structural limitations. At speeds less than the maneuver speed, the limit load factor is not available aerodynamically and turning performance is aerodynamically limited. At speeds greater than the maneuver speed, CLmax and maximum aerodynamic load factor are not available and turning performance is structurally limited.

Each of the three limiting factors (aerodynamic, structural, and power) may combine to define the turning performance of an airplane. Generally, aerodynamic and structural limits predominate at low altitude while aerodynamic and power limits predominate at high altitude. CFIT is prevented by awareness of proximity to terrain - nothing elseTrue, but folk have a habit of boxing themselves in. The US lists a number of accidents each year where folks get trapped by flying into canyons, we had a Beaver here that may well have fallen foul of the same with the loss of all onboard. Refuelling one day and a C 206 pulled up, two young lads with girl friends, shrubbery hanging from the airframe, had flown into a canyon in absolutely foul weather, pulled up when they reached the end of canyon clipping the vegetation - lucky. Typical accident.

https://dms.ntsb.gov/pubdms/search/hitlist.cfm?docketID=60163&CFID=2587931&CFTOKEN=80d6b90dec79df5a-E35F903B-938B-38C1-3CD940D0EBE66555

Take note of page 16 at https://dms.ntsb.gov/public/60000-60499/60163/606411.pdf

Not a laughing matter

https://www.youtube.com/watch?v=r2MVDY8o7Bs

[Maoraigh1]

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20190425X83902&AKey=1&RType=HTML&IType=FA
The reported last message from this fatal instruction flight, with a student pilot, appears relevant to this thread. April 2019 accident.

[Pilot DAR]

flying at Va and turning/banking to point of stall burble would give you 3.8 "g" (normal category limit) and the minimum radius turn, and no ability to overstress the aircraft. No one is going to get G-loc there. It gives you the minimum radius turn,

Yes Megan, that point is clear to me, and a good benchmark in maneuvering for a pilot to understand. However, while protecting the airframe from being overstressed (because it will stall first) abrupt maneuvering at Va will bring the airplane close to loss of control. That loss of control protects the airframe from structural damage, by releasing the lift in a stall - and you're not in controlled flight any more. As wisely said, at least it won't be a CFIT anymore!

Va is a wise and safe reference speed for maneuvering - at altitude. If you're in a situation where maneuvering abruptly at Va is your means to best assure a safe exit from the situation, you're way past safe anyway. If the notion is to fly around at Va, so at any moment, you could apply full control input to maneuver around a sudden surprise, well, that's technically correct, but way beyond good airmanship!

This is why this topic is worrisome for an online discussion, it presupposes a lot of cautions which should be a part of a bigger discussion.

[megan]

If you're in a situation where maneuvering abruptly at Va is your means to best assure a safe exit from the situation, you're way past safe anyway. If the notion is to fly around at Va, so at any moment, you could apply full control input to maneuver around a sudden surprise, well, that's technically correct, but way beyond good airmanship!The following accident involving the inflight break up of a 210 discusses the possibility of the pilot applying excessive aileron whilst above Va to avoid birds. They discounted the possibly, but couldn't rule it out. Wedge Tail Eagles are common, weighing in up to 13 pounds, 9 foot wing span, soaring to 6,000 and higher, and reluctant to get out of your way, done much dodging myself. The pilot had suffered minor facial injuries from a previous bird strike.

https://www.atsb.gov.au/media/5776004/ao-2017-103_final.pdf

Risks abound whatever you do.

[Big Pistons Forever]

The video posted by Megan is a demonstration of gob smacking idiocy. For GA most CFIT accidents seem to start with a progression of VMC into marginal VMC into IMC. I teach my students that before you fly in poor weather you have to set hard limits. I recommend starting with 3 nm in flight visibility and 1000 ft AGL. Determining actual flight visibility is pretty easy with modern GPS moving map displays, if you can't see that geographic feature 3 miles in front of the little airplane on the moving map turn around. The same with altitude, if you can't maintain good VMC at your 1000 ft AGL minimum altitude then turn around.

I also tried to get all my students some exposure to actual marginal VFR conditions. There is a small airfield 11 miles from my home base. to get to it you have to pass over an inlet and up a bay. On several occasions I have had students get spatially disoriented in this short flight. Every student has remarked how difficult 700 and 2 actually was compared to how they thought it was going to be.