Pilot induced oscillations

[Mayfield]

Some food for thought on the subject of PIO. I would like to toss out some ideas and possible explanations for comment.

First, most of us have ridden bicycles so we will start there.

If we painted a foot wide stripe on the ground, could we ride our bicycle along the stripe without going over the edge? I suspect most of us could.

If we placed a foot wide beam between two skyscrapers, could we ride our bicycle along the beam without falling off? I suspect most of us could not and would hurtle downward within seconds.

Why is this so? The task is the same mechanically. The boundaries are the same. The consequences of exceeding the boundary are much different.

My thoughts on this were stimulated by a paper submitted to the Society of Experimental Test pilots (SETP) by a gentleman named William Gray from the Air Force Test Pilot School.

I hope this thread generates some discussion. I’ll keep this first one brief.

The author discusses two tasks:

1. Point Tracking

2. Boundary Tracking

A point-tracking task would be something like maintaining altitude, airspeed or heading. Most of the time we, as pilots, will except some deviation from the desired point. That deviation might be 100 feet of altitude or 10 knots of airspeed. The “comfort” band is self-imposed. The consequences of exceeding the self-imposed error limit are benign.

The pilot “gain” in a point tracking task is relatively low. That is, the pilot will make relatively small corrections in his attempts to maintain the point.

As the pilot gently oscillates through his altitude point, for example, a PIO with low pilot gain is occurring.

A Boundary tracking PIO is a little more complex, according to the author. There are at least two types of Boundary tracking PIOs. The first is called Boundary Avoidance PIO.

A Boundary Avoidance PIO has higher pilot gain than a normal point tracking PIO. Usually, pilot gain is limited in boundary avoidance tracking by the pilot’s comfort level. This comfort level may be G changes, airspeeds, etc.

A point tracking task, which normally involves low pilot gain, may become a boundary-tracking task.

An example would be maintaining altitude within 50 feet on a commercial pilot check ride. Normally altitude maintenance is a point-tracking task with an error band set by the pilot. High pilot gains are not necessary because the error band is self-generated.

This same task becomes a boundary-tracking task when a boundary, and not an error band, is established. Something bad will happen if the boundary is exceeded. The pilot will fail the check ride. A boundary-tracking task has an inherently higher pilot workload and thus a higher pilot gain than a point-tracking task.

The second type of Boundary tracking PIO occurs during a Boundary escape task.

A boundary escape task, as the name implies, is a task that must be accomplished to avoid crossing a boundary that is deadly. Avoiding a wire while flying low, avoiding impacting the ground, avoiding an over speed or over stress condition while flying, or.........falling off the foot wide beam between the skyscrapers.

Mr. Gray postulates that in a boundary escape input that pilot comfort no longer limits pilot gain. Pilot input gain is limited only by the pilots strength or control stops in a fully developed boundary escape PIO.

He contends that a pilot will make a high gain control input to avoid crossing what the pilot perceives as a lethal boundary and that he will hold that input until he is back inside the opposing lethal boundaries.

The problem arises as a function of rate of change. By the time the pilot realizes he can reverse his control input he is already at the opposing boundary. With each oscillation the boundary is exceeded more and more.

Just imagine how horrific this would be if the aircraft you are flying is statically unstable. In a statically stable machine, if you could force yourself to just let go of the controls you might have some chance.

In a statically unstable machine, particularly a rotorcraft, you’re damned if you do and you’re damned if you don’t.

I would be highly interested if some of the folks that have an interest in modeling closed loop systems would think about this PIO model.

Hope to see input,

R/S

Jim Mayfield

[C. Beaty]

Hmmm…., A stability analysis that includes the pucker factor.

For those not familiar with terms like “gain” in closed loop systems, imagine a PA system with the gain cranked up too high. You get what Ben Mullet referred to as howl around.

Pucker yields double jeopardy with dynamically unstable gyros.

The pseudo stability of the offset gimbal rotorhead vanishes with a death grip on the stick in addition to the pilot’s gain being cranked up.

Bensen, in his training manual, cautioned learning pilots not to exceed an altitude of a few feet for the first ten hours or so.

I suppose pucker factor was part of his reasoning; most fatal bunts occur at pattern altitude but another contributor is the loss of familiar objects from the student’s peripheral vision. Power poles, trees and the like form a subconscious attitude reference.

[birdy]

I................ nah,I won't. :rolleyes:
Interesting thread sofar Jim.I wish you luck mate. :)
[I'v got some comments but.................. we'll see.] :D

[Mayfield]

David,

I, for one, would like to know your thoughts on this subject.

It appears to me that the more light that is cast on a subject the harder it is for the truth to hide.

I hope some of the more analytically minded among us gives this area some thought.

R/S

Jim

[Vance]

In motorcycle road racing when someone falls in front of you the tendency is to run into them because of "target fixation" (you go where you look). I had to learn to look anywhere but the wreck, and some people didn't learn and they would become part of the accident.

In the bicycle example, when it is a line you are suposed to follow it is easy to focus on, on the other hand if there was a lot of drop on either side of the beam it would be hard to not look down.

Not focusing on the hazard was always a difficult learned responce for me. I think that any hazard atracts my atention, the bigger the hazard the more attention is drawn to it and the harder it is to overcome the atraction with learned behavior. For me it is a little like learning to not stop my fall with my hands. The more violent the impending impact the more I want to put my hands out.

I make better decisions when I have all my safty gear on. I would think that in an unstable giro that I would stop trusting my training sooner because I feel more at risk, my beam is narrower and it is easy for me to look down and focus on the danger. Am I saying the same thing?

Jim, your explanation sounds more elegant. I love it when you describe managing anxiety. Anxiety management was always key in expanding the performance envelope of the racing motorcycle. I hope I can learn to manage the expanded world of anxiety in flight. Thank you for the help, I feel like folowing this thought has been cathartic.

Thank you, Vance

[mceagle]

I would suggest that Bensen also concluded that the 2 ft AGL hope also precluded the chance of PIO, simply because there was not enough room between the wheels and the ground to get into a deadly situation - just your common or garden beginners triple tumbling pass in a half pike position.
The pucker factor as Chuck accurately called it, was very noticable to me when racing speedway. A more difficult track or a sudden increase in horsepower left you tensed up for a few laps until you came to grips with the new conditions. While you were tensed up, your driving suffered considerably, especially at thre hands of the ingrained locals. There was nothing more frustrating than fighting the clay with both hands, thinking that you are going as fast as man and car could go, and looking over and seeing another driver out in the loose, passing you on the outside and waving to you with one hand while doing so. I guess I can understand how beginner gyro pilots feel while watching a demo from a good experienced pilot.
My first gyro circuit went mostly without escaping the security blanket, although a pucker factor came in when I noticed the rotor tach falling on the downwind leg. The circuit was cut short and the ensueing rough landing was testament to the extra load applied to what should have been a normal landing (something that I had done 100 times before doing hops)

[Cobra Doc]

My quote in my signature line is actually my own quote. I used it on trainee air traffic controllers. The worst scenario for new controllers was the training environment around Ft. Rucker, AL. More specifically, the Troy airport (TOI for the AirNav buffs). At 11:00 am and 4:00 pm we always had Army helicopters mixed Navy and Air Force airplanes trying to get in just one more approach before they had to get back to Rucker, Whiting or Maxwell. Add in the civilian traffic endemic to the field and Sikorsky Rebuild doing test flights. The pilots tended to add their get-homeitis stress to the nomal pressures of ATC. A new controller would start to crumble until I reminded them, with my slogan, that things are cool. Nothing is going on and nobody is about to become spam in a can. When things did go south, I was there. Sometimes I would take the position, other times just the fact that I was there and could take the radar was enough to relax the contorller enough that he or she could continue to do the job. Stress is all just a matter of perception. Could I ride a bike accross the 12" board over the Grand Canyon? I doubt it, but once I fell I would have a minute with nothing to do but enjoy the scenery!

[PW_Plack]

Perhaps riding a bicycle on a foot-wide beam two feet off the ground, then slowly raising the beam AGL, would allow us to reach the required confidence in steps.

I once asked an experienced gyro pilot why some self-taught guys seem afraid to climb above treetop altitude. He supposed that Bensen's self-instruction syllabus, with heavy repetition of 2-foot AGL manuevers, tended to produce pilots who were overly reliant on the visual cues of low-level flight, and increased their risk of PIO at pattern altitude. If that's true, Jim may have found the engineer's way to describe it.

[birdy]

Why do you think I'm afraid of hights??

[Mayfield]

Good morning David,

I do not know if you are afraid of heights David. I only know that I am.

The role of boundary escape tracking in PIOs is fascinating to me. I suspect that it could be modelled and used as a design tool.

Specifically, I am curious about what the triggers are in a boundary escape PIO.

As I think about this in laymans terms it seems to me that the bicycle analogy may have some value.

I am certain that I could not ride the foot wide beam suspended over the drop.

I am also fairly certain that I could ride the foot wide stripe on the street.

Where does the break point come. To give a couple of examples:

1. A hundred foot wide beam? I think so.

2. A twenty foot wide beam? Again, I think so, but I suspect that I would be very aware of the edge.

3. A ten foot wide beam? Maybe....! I would be highly focused on the edge of the drop off. My "gain" would certainly be cranked up.

4. I am almost certain that a 5 foot wide beam would be nearly impossible for me.

This seems to mean that the proximity of the lethal boundary in time and/or space, has great impact on pilot "gain."

Can this concept be modelled as a design tool to make the boundary, in a practical sense, farther away?

I do not know the answers. I am having difficulty framing the question.

I think that some hard charging Phd aspirant could do his dissertation on this subject.

Neat stuff though,

Jim

[PTKay]

Jim,

have you been following the discussion on the Airbus crash in NY.

It was also an obvious case of PIO (yaw in this case), and the
extra "gain" in the young F/O reactions was trained in by AA sylabus.
(As far as I understood it).
The wake turbulence the AC hit, pushed the F/O reaction to "boundry mode"?

So, PIO is not only a gyro phenomenon. It kills also in "heavy metal".

PTKay

[Mayfield]

Paul,

Thanks for your input.

Yes I was aware of the Airbus yaw PIO.

It is my opinion that PIO is very common. It would be fun to instrument an aircraft wherein the pilot was doing simple point tracking tasks. For example holding a heading/altitude on a cross country flight.

I suspect we would see long, gentle, sine wave type tracks as the pilot checked his heading/altitude every few seconds and then made corrections.

I'll bet if we instrumented the same airplane while the pilot was flying a published instrument approach we would see the tracks with sharper excursions and returns to heading because the pilot's "gain" was turned up. The point tacking task of holding heading/altitude has evolved into the boundary avoidance task of holding heading/altitude within pretty well defined constraints.

If we loaded his aircraft at an aft CG while he was shooting the approach, I believe we could begin to see boundary escape behavior as the pilot began to chase the pitch excursions.

Up and away from the ground our airplane pilot would have to avoid pulling the wings off as he over controlled the airplane or a loss of control as the cycles became to fast for him to keep up with.

In a rotorcraft, I believe it is even more critical to maintain the G load within limits to avoid a catastrophic unload.

I am giving this significant thought. I am pleased that others are following the thread and providing input.

R/S
Jim

[Victor Duarte]

Talking about PIO .
a silly question : do you think a damper in the front of the stick could avoid a too fast forward imput? just throwing a quick idea...
thank you

[mceagle]

Victor, others will correct me if I am wrong but in my experience PIO is perpetuated when the pilot is too slow in the reflexes, not too fast.
This could also have implications in what Jim is referring to. If reactions are too slow and recognised as such, then the actee is likley to overcorrect to compensate.

[Mayfield]

Tim,

I agree. I believe that a basic tenet of Mr. Gray's paper is that when the boundary escape mechinism is triggered the pilot not only makes a large correction but that he holds it until he is inside the boundary.

If the boundaries are close to each other, waiting until you are back inside the boundary is far too late and you will shoot out the other side.

In normal point tracking tasks we, as pilots, learn early in our training how to lead a roll out or a level off.

It appears that in a fully developed PIO resulting from this boundary escape behavior that the pilot is acting more like a servo with no damping.

R/S

Jim

[Victor Duarte]

Tim, Thanks,
that's an interesting point of view. I ve read in this forum that the kind of "panic" reaction could also cause PIO, so, if i understand correctly, the imput must be constant and balanced or much later than "too late" (meaning in the freq of the airframe pendulum).
what do you teatch to your students ?

another question : not a pilot yet, i just feel the PIO could begin by a nose down or a nose up... does it make sense ? are there 2 different attitudes in whitch the PIO could begin and is the appropriate response identical ?

Thanks

[birdy]

PIO.
PILOT induced .
The only thing that MAY help stop POI is some type of dampener.[H stabs,steering dampeners on cars,.......].
The trouble with any dampener is it always works, at the same rate in all conditions.
And I'll put my head on the block again and say ,sometimes a dampener isn't benifitial.
So as to not start another endless sh1t fight,I'll use the auto's hydralic steering dampener for an example.
In MOST situations it is of benifit,but there are occasions where it can be down right dangerous.
Again,I'll only speak from experiance,experiance from years of Practice.
When we're mustering here,we have modified 4+4's as ground backup[ bullcatchers].
These machines would never pass a roadworthy test in a million years,but they are the fastest,most agile,and more importantly,SAFEST machine for such a job.
AND THEY DON"T HAVE STEERING DAMPENERS.
WHY??
Coz when your tearing through the scrub,with visability of less than 20 yards,at 40mph,not only watching where your going but also trying to keep an eye on the critter your trying to catch, the last thing you need is some mechanical devise that slows you ability to weave through the timber.
Especialy if your do'n the above in reverse.


To stop a piolt induced anything is to stop the pilot inducing.
Trouble is, we're all human,and we'll always make mistakes.
The trick is to figure WHY all humans make the same mistake.
A gyro should only crash from human intervention for 3 reasons.
The pilot either,
1; isn't relaxed and over corrects with inaproperate control inputs.
2; dosn't understand what is happening airodynamicaly and applies incorrect inputs.
3;dosn't know what the correct inputs are .
Having a solid understanding of these will prevent any PILOT induced stuffups.

Out of the three I think the first is the most important.Don't try ANYTHING in the machine till you can fly round in reasonable lumpy air without needing to concentrate on flying.[a good indercater is when you find your self sing'n your most hated tune to yourself while holding the machine level,and arriving at your destination with no recollection of the trip over.]IOW,flying by instinct.

PIO is nothing more comlpicated than a human brain being overloaded by 'self preservation' demands before it had the time to programm itself for the situation.

Most people will PIO any machine [including cars],if they don't give they'r subconsious enough time to programm itself to the control/responce rates,and it's the RATE of responce from a control that is the most important part of smooth mind/ machine synchronising.


If you started your beam walk'n from 1',and gradualy worked your way up to 1000' on the same plank you'll think to your self when you get to the top 'I can't belive I was scared of hights'.
But if you don't give your mind time to adjust to the increasing hight,it'll panic and you'll loose your balance.
You'll know your push'n it too hard when you feel uneasy.That's when you slow down.
If you don't,you'll be think'n "I shoulda slowed down a bit then" on your way to the ground,with out a chute.

[Jazzenjohn]

My opinion is that if the different scenarios were tested the result would be that the rate of correction would be increased from point tracking, to boundary tracking, to boundary escape. That would imply that a rate controlling damper would be of some benefit for inexperienced pilots until experience and training overcome impulse. After that, the pilot and the intended use would dictate whether to keep it or remove it.
I would venture to guess that the reaction to the movement towards the boundary would be less of an issue.

[PW_Plack]

"There's no shame in dying unless you had bullets left."

In a pilot's approach to a fatal boundary there is a subconscious decision to hold a control deflection large and/or long enough to risk overshoot, prioritizing getting out of the more immediate danger first, and dealing with the overshoot second.

Perhaps we could apply technology to influence a pilot to reduce the duration of the control input by providing a signal when the deflection has been of adequate duration to achieve the desired result. A PIC processor fed by the appropriate sensors could predict when a control input was long enough to hold the aircraft within boundary, and provide an audible or visual signal when the computer could predict an adequate correction. Perhaps an instrument with a display like a gyroscopic attitude/heading indicator, but moving in a way to predict the future two or three seconds ahead would work.

If this device could be made to work reliably, it would be tempting to bypass the pilot, and give it authority over control linkages, but I'm not sure anyone would trust it.

[birdy]

I'm not sure anyone would trust it.

I'd be one of them 'anyones'.

I can't see why it wouldn't work,but it'd need to be programmed to account for EVERY situation.I wouldn't like a computer tell'n me not to reaf the stick back,to avoid a tree, only because it don't know bout trees.

Flying by feel is much easer on the brain coz its natural but if you thow in even more information ,like warning buzzers,lights or instruments,it'll delay a possably critical input even more.
Programmed reflexes [subconsious] will work near as fast as a computer, and much faster than the consious thought process.

That would imply that a rate controlling damper would be of some benefit for inexperienced pilots until experience and training overcome impulse.

Spoton john,giving the mind time to "programm" in a safe enviroment.

[Jerseywing]

I don't know... You look at a child learning to ride a bicycle, the corrections are extreme till the "feeling" is there. The feeling is your body and senses learning new sensory inputs and adjusting to them. Once learned they become second nature and the oscillations go away. I don't see learning to fly as any different. You need to learn the "feel" of things and the instructor is there to "grab your seat and hold you up" till you get it right. I know for myself if I think too much about flying I start to oscillate but when I "get distracted" I fly S&L. For me it's a matter of learning the feel and letting it go naturally.
I don't know if this makes sense but...

[birdy]

a child learning to ride a bicycle
That is a perfect and realistic annalogy Michael,and one most every one can relate to.
Once your subconsious is tuned to the bike,even a child thinks its a pice of cake.

[PW_Plack]

Dunno, Birdy, I have the same problem with a rate damper you have with the computer intervening. Both block control inputs that might be beneficial at some times.

Is the rate really the problem, or is it the newbie pilot holding the control input too long?

As for learning the machine so it's second nature, the problem is we have 20,000-hour ATPs dying before they get that far. Get in a thousand gyro hours, and all this stuff is probably moot point.

[mrford61]

Its all a bit like when you was a young bloke and trying to hit on a sheila that is way out of your league.

Your usual cool, calm demeanour deserts you and your easy witty conversation and glib responses are replaced by gibbering , ridiculous babble that you can hardly believe you are self conciously sprouting. :o :o :o :o

[birdy]

Fair point Paul,but a dampener will prevent any sudden inputs,when a newby should be keep'n it light and smooth.[Personaly,I reckon there shouldn't be any interferance between the pilot's hand and the rotor, from the start.]
And when I said RATE,I woz refering to the rate of LAG.Rate is probably the wrong word. Lag interval maybe more accurate.
It's the input.......lag.......responce that causes the second nervous input,before the first input is responded to by the machine.
If the newby was aware,subconsiosly,of the lag,then it's less likly he'd hold the control too long,coz he'd know it'll catch up,after the lag.It'd be the lag that'd cause him to over hold the control.

I think your last point [BTW,wots a ATP] is another problem.How do you tell a 20,000 hour ATP that he don't know??

[PTKay]

Just a nice example of a PIO (in roll) on a difficult
landing in an Airbus:

http://www.flightlevel350.com/picwindow.php?cat=19&pic=116

I think, this picture confirms the theory, Jim was presenting.
The closer to the ground ("lethal boundry" in this case),
the pilot, (until then fairy well coping with the cross wind)
starts to overreact to the roll changes and falls into oscillation.
(He made full 5 oscillation cycles just few feet over the runway !)

In this case he was good enough to recon his mistakes,
stop turning the yoke left and right, just arresting it
and giving full power. This one went well...
On non of the oscillation cycles the gear touched the
ground, but if you watch closely, there were just inches...

I know nothing about the pilot or the other circumstances of the
event, but this is, what I suppose, has happened.

Anyway, an interesting ground school discussion film. ;)

PTKay

[Heather Poe]

Another real-world scenario that people can relate to is driving on ice and snow. Usually small control inputs are sufficient to keep the vehicle under control. If you start to slip and slide on the surface, people are trained to maximize the chance that oscillations will be damped by turning in the direction of the skid and minimize their control inputs, until traction is reacquired, and then proceed. Many people understand that if they overcorrect in these situations, they make the situation worse. I have had a relatively small number of hours of incomplete training, so I can't say whether this is standard, but perhaps practice of this sort should be a part of flight training.

[Heather Poe]

Let me rephrase my previous post. For aircraft that have dynamic stability, are student pilots explicitly trained NOT to provide control inputs in some situations?

[bones]

PIO is nothing more comlpicated than a human brain being overloaded by 'self preservation' demands before it had the time to programm itself for the situation.

Birdy that is soo true, a few years back when i was rigging not ringing, to start a job that was already going was so hard because the building was already so high that you didnt have the time to climatise to the hieght, so on the first day the worse thing that could happen would be to be sent up to 30-40 meters to start work, but after a week or so, it was nothing to be walking a piece of 2" angle iron out to the side of a raker some 3-4 meters, with nothing but thin air under you for the 30-40 meters, you just learn to trust yourself and to look at where your foot is going and not past it, the same thing for flying, trust what you need to do, not what could happen.

[PTKay]

Anorter good example:

I have a 7 tons, steel river yacht, flat bottom, no keel, water jet propulsion.
It is 43' long and 10' wide but goes just 1' deep. It has also no steer blade.

You can imagine how direction unstable it is, and, by this mass, how slow
reacting.

The only way to keep it on course is by steering with the water jet.

After some training, like Birdy explained, my hands were moving on the
steering wheel very rapidly, unconsiously and I was able to steer
straight without any problems. The trick was to fix to the point on
the horizon, fix it to the point on the front railing and follow it.
(I think you can define it as "point fixed" pilot reactions).

For the outside viewer it seemed really ridiculous, what I was doing, because
I was reacting quite rapidly to smallest movements, not visible (or apparent)
to them, so it looked like stupid, unnecessary fight with the hardware.

Once, we were travelling on a narrow channel with concrete banks with a
friend from Denmark and his family. He is a very self confident and arogant
person and started laughing at my style of steering.

I immediately suggested he should take over,
if he thinks he can do better.

Of course, he immediately started the "boundry mode" trying to avoid
hitting the banks. He turned the wheel to one side, and the 7 tons didn't react
as fast as he expected, so he turned even harder to avoid a bank...
Then the other bank stared getting closer and closer...

As you probaly expected, he hit the bank already by the second oscillation cycle,
his kids and wife almost falling into the water, but fortunatelly only paint scratch
on the steel hull and lots of noise. :)

He immediately gave over to me and stayed quite for the rest of the trip...

I hope it's a good example of "point" vs. "boundry" mode.

PTKay

[Mayfield]

Please forgive me if I keep beating a dead horse, but I find this fascinating. I am not sure there is any practical application for us folks down here at this end of the aviation market, but if it increases our understanding of the mechanics of PIO it will be worthwhile.

Right now, even though Gyros are my primary interest, I am looking at PIO as a phenomenon that effects all man/machine relationships. For me, if I can begin to understand the basic mechanism, I can then try to apply this understanding to specifics.

Paul's post #26 contains what I believe is a neat clue.

One thing that I noticed was the sound of the turbines spooling up, the pitch to climb attitude, and the immediate stopping of the roll PIO occuring together.

It appears that once the boundary escape mechinism in the pilot was turned off that he/she immediately stopped the inappropriate input.

Comments?

R/S

Jim

[KenSandyEggo]

Caan you imagine having been a passenger on that flight? I bet it cost each one 5 years off their life.

[Victor Duarte]

From that discussion, comparing with cars. I feel thet the better way to control PIO is to know the reactions of the machine.
years ago i had a piloting lesson on snow, and the main source of over turn is over steering and re-oversteering... if you drive with two fingers and let it slide gently, you will control the car better i learnt to "anticipate".
The problem is that you can explore a car's reactions but can you explore so safely a PIO gyro behaviour ?
thanks

[darrellwittke]

I watched a training video perhaps a month ago on something called Recognition Primed Decision-making. The long (2 1/2 hours of mostly boredom) video detailed how the U. S. Army contracted with a psychology group to learn how people make decisions under stress. What the psychologists assumed is people made decisions by comparing decision A to decision B to however many options time and intellect could arrive at.

What they found by studying firefighting incident commanders and others in high risk and complex scenes is that they went straight to a decision from their previous experiences that most closely resembled the current situation.
A L. A. assistant chief gave the best analogy, that each of us has a set of memories much like the old round slide carousels used to give slideshows. Our mind whizzes to that slide which most closely resembles our current situation and we make our decisions off of that. The study emphasized and supported the value of experience.

The U. S. Army, it being to dangerous to give officers decision making experience in combat situations, has (or is) developing video training (computer games) to try to give as close as possible visual, auditory and time stressed decision making scenarios to trainees.

This stuff may be old (the video looked dated) but I thought I would mention it here just in case it may be relevant.

[PW_Plack]

Birdy, sorry, perhaps not a worldwide term. ATP = Airline Transport Pilot.

[Alan Coats]

Try this for an example of Point Tracking and Boundary Tracking. I think some of the principals you have been discussing apply to this exercise.

http://www.mtbireland.com/dodge.html

Alan

[Texas Armadillo]

Wow, I'm going to have to go back and read this thread a couple of times. I hope I'm not double posting something posted earlier.

On a much simpler level than what I've seen posted here, the mention of the bicycle on the 1 foot stripe and accident fixation, bring to mind something... (incredible isn't it?) Keep in mind my balance ain't the greatest.

When I first learned to ride heavy street bikes, I had trouble stopping smoothly. Then someone mentioned that I needed to stop looking down at the road in front of the bike when I was almost stopped. Instead look out way ahead and use my periferal(?) vision to stop at the stripe.

I found that worked very well for me. Focusing way out in front of the bike lessened my control inputs, and stopping easily, smoothly, and on one foot became a breeze.

So in the bicycle example, the rider is now worried about the width of the board. So he is looking down at it instead of the end way far away. While looking down, the control inputs are over-reacting, jerky, and uncertain, as he sees how close he is getting to the edge, and the loss of balance is assured.

js