to HSI or not to HSI

"Michael" wrote in message
om...
"Richard Hertz" no one@no one.com wrote
Can you explain why that is the one advantage (BC)/revers on localizer,
and
why that is so?
Do you mean to say that people confuse which color sector they are in on
a
localizer due to "reverse needle"?

Yes, that is exactly what I mean to say.

If so then it is a training issue, not a
technology issue.

Oh man, here we go. You've just touched off a religious debate.

In real life, I run a department that designs instrumentation for
process environments. What that means is that engineers design it,
but generally non-engineers (plant operators, meter readers,
technicians) install and use it. These days, most instrumentation has
software in it, so it should not come as a surprise that I rose into
that position from software engineering.

In the process, I learned a lot about user interfaces. There are two
kinds of user interface bug. There is the kind where the user
interface acts contrary to design, in a useless or unpredictable
manner in a given situation (coding error) and there is the kind where
it acts as designed (intentionally or unintentionally), in a manner
that is predictable and useful but, in certain situations,
counter-intuitive to the operator (design error). The first kind is
unusuable in those given situations. The second kind is usable,
provided you read the manual and are aware of how the system will
behave. There are those who believe that this means it's not an error
- that you should simply RTFM. In other words, that it is a training
issue. They are wrong.

I do not disagree.


The "reverse" indication of a conventional CDI is a design error. You
can work around it. I have. I had to shoot a LOC BC approach with
engine failure at leveloff (simulating a failure of the engine to come
up on the powerup for leveloff) followed by a single engine missed
approach. I passed - meaning I executed the approach and miss to ATP
standards, and I have the certificate to prove it. Nonetheless, a
couple of times I found myself, with the needle half a dot off,
applying the incorrect contol inputs before I "caught" myself. So
clearly the training worked - I corrected before I deviated beyond ATP
standards - but that doesn't mean that the design is correct. It's
not. On an approach, you're used to correcting towards the needle.
Under normal conditions, you should have the situational awareness to
know what you are doing, rather than just correcting by habit.
However, in emergency conditions where the workload becomes high,
there is a tendency to revert to habit. In other words, the operation
becomes counter-intuitive.

Here disagree - the current use appears to imply a "design flaw" but that
is only because of imporper use and instruction of the instrument. It does
not "point" to the course, rather it shows what sector of the localizer
course you are on. (shaded or unshaded.)

It is a back course - meaning you are coming from the other way. You know
this. Clearly the instruction should be corrected - it is a lot cheaper
than everyone buying HSIs. I have no difficulty with localizer front or
back course, though I am certain I would mix things up if I had been taught
the improper (but more common) use of the needle pointing to the course
(except for BC which is different)



Sometimes this is unavoidable, but where this is done for no good
reason, it's simply bad design. It's really quite simple to modify a
conventional CDI for "reverse" sensing - all it takes is the addition
of a simple DPDT switch, and the needle will act correctly on the BC.
Thus I have to say it's done for no good reason. Only in aviation is
somehting like this not done - because this is how we've always done
it (and because the FAA would make such a modification
cost-prohibitive).

The UK (and I believe other nations) will not certify LOC-BC
approaches because the potential for error is believed to be too high.
I don't agree with this - I consider the potential for error to be
adequately low with proper training - but the addition of a cheap,
simple, and reliable part to the CDI (or replacement with an HSI)
eliminates the potential for error - and is thus clearly an advantage.

And what is thins part?

I contest that ensuring the blue and yellow colors on the instrument and
proper training would avert the confusion.


Michael

"Richard Kaplan" wrote in message
news:1100448898.Cxp1I/EOmK8jzRh1wjL0fA@teranews...

wrote in message
...


So why then teach the solution that requires doing it the hard way?

The easiest way to interpret a CDI needle 99% of the time is to think of
it in terms of "left" vs "right".

And that is bad.


A more generalized solution which thinks in terms of sectors does indeed
make a back course easier for 1% of instrument flying but also makes the
other 99% of instrument flying less intuitive.


No, not less intuitive - you just believe so as a product of your training.


--------------------
Richard Kaplan

www.flyimc.com

wrote in message
...


It is just as easy ti interpret a CDI needle in terms of headings and
course intercept angles if you are taught properly to do so.

Please explain to me how to do this.

--------------------
Richard Kaplan

www.flyimc.com

"Richard Hertz" no one@no one.com wrote in message
t...


No, not less intuitive - you just believe so as a product of your
training.

OK, so how would you teach use of a CDI to a brand new pilot?


--------------------
Richard Kaplan

www.flyimc.com

The OBS ring is set to a course heading.

The 2 hemispheres on the ring correspond to the two sides of the
course line. A northerly course has an east and west side. A
northwesterly course has a southwest and a northeast side.

Any of the 179 headings which are on the hemisphere on the needle side
will intercept the course, at 179 different angles. (Actually, 89
angles in one direction, and 89 angles in the other direction, and one
90-degree intercept) Any of the headings on the other hemisphere
will fly away from the course.

By flying a course, for example, 30 degrees off the top of the OBS, on
the needle-side hemisphere, will intercept the course at an angle of
30 degrees. To intercept at a 30 degree angle outbound, fly a course
30 degrees off the bootom of the OBS, on the needle side.

Likewise for any other angle.







On Sun, 14 Nov 2004 19:37:44 -0500, "Richard Kaplan"
wrote:

wrote in message
.. .


It is just as easy ti interpret a CDI needle in terms of headings and
course intercept angles if you are taught properly to do so.

Please explain to me how to do this.

--------------------
Richard Kaplan

www.flyimc.com

Start by explaining that the ONLY information provided by a VOR head
is the position of the aircraft with respect to two lines.


There is NO directional information provided, and without some other
instrument to provide directional information, it is useless as a
navigation tool.



On Sun, 14 Nov 2004 19:38:59 -0500, "Richard Kaplan"
wrote:


"Richard Hertz" no one@no one.com wrote in message
et...


No, not less intuitive - you just believe so as a product of your
training.

OK, so how would you teach use of a CDI to a brand new pilot?


--------------------
Richard Kaplan

www.flyimc.com

wrote in message
...

By flying a course, for example, 30 degrees off the top of the OBS, on
the needle-side hemisphere, will intercept the course at an angle of
30 degrees. To intercept at a 30 degree angle outbound, fly a course
30 degrees off the bootom of the OBS, on the needle side.


That is fine as an explanation of which direction the CDI needle will move
in any given situation.

It does not make any easier the practical question of which way to point the
airplane when the CDI needle is deflected at any particular time.

And it particularly does not make any easier the practical question of which
way ot point the airplane when flying a localizer, where there are not 179
different courses that can be flown.

Your example focuses on VOR navigation, where there is never a need to
navigate with reverse sensing -- just turn the OBS knob 180 degrees.
Reverse sensing is only an issue on localizer approaches.

--------------------
Richard Kaplan

www.flyimc.com

A localizer course is no different in this respect. If you are not on
the course, there are 179 headings which could intercept the course.
2 headings are parallel headings, and 179 headings take you away from
the course.

This has nothing to do with radios. It is simple geometry. It
applies to any line in space.

As far as radios are concerned, if you have the OBS ring set to the
single localizer course, and you are west of course, it will indicate
west of course, whether front course or back.

There is no such thing as "reverse sensing". The nav radio senses a
localizer course on the back course EXACTLY the way is is sensed on
the front course.

The only thinkg that gets reversed is the pilot's thinking, which is
why the concept is found so confusing by students. It is not because
of inherent complexity, but because it is taught in an unnecessarily
complicated fashion by flight instructors.



On Sun, 14 Nov 2004 20:47:32 -0500, "Richard Kaplan"
wrote:

wrote in message
.. .

By flying a course, for example, 30 degrees off the top of the OBS, on
the needle-side hemisphere, will intercept the course at an angle of
30 degrees. To intercept at a 30 degree angle outbound, fly a course
30 degrees off the bootom of the OBS, on the needle side.


That is fine as an explanation of which direction the CDI needle will move
in any given situation.

It does not make any easier the practical question of which way to point the
airplane when the CDI needle is deflected at any particular time.

And it particularly does not make any easier the practical question of which
way ot point the airplane when flying a localizer, where there are not 179
different courses that can be flown.

Your example focuses on VOR navigation, where there is never a need to
navigate with reverse sensing -- just turn the OBS knob 180 degrees.
Reverse sensing is only an issue on localizer approaches.

--------------------
Richard Kaplan

www.flyimc.com

wrote in message
...

As far as radios are concerned, if you have the OBS ring set to the
single localizer course, and you are west of course, it will indicate
west

I say again.... when things are bouncing around in the airplane and you need
a quick answer, which way do you turn when the needle is deflected?

For 99% of pilots, it is MUCH easier to turn in the direction of the needle
than to consider which geometric side of the course will result in what sort
of deflection. It is MUCH easier and safer if interpretation of the needle
is simplified in this format.

"Forward" vs. "Reverse" sensing are indeed simply paradigms based upon the
pilot's perspective of the world. For most pilots, the "Forward" sensing
paradigm is much easier to interpret than your alternative (though
acceptable) geometric paradigm. I agree that the "Reverse" sensing paradigm
is a bit harder than your geometric paradigm, but that accounts for a small
minority of time for most pilots compared with time under the "Forward"
paradigm.

--------------------
Richard Kaplan

www.flyimc.com

wrote in message
...

Start by explaining that the ONLY information provided by a VOR head
is the position of the aircraft with respect to two lines.


There is NO directional information provided, and without some other
instrument to provide directional information, it is useless as a
navigation tool.

Thank you. It is amazing that it has gotten to this.




On Sun, 14 Nov 2004 19:38:59 -0500, "Richard Kaplan"
wrote:


"Richard Hertz" no one@no one.com wrote in message
. net...


No, not less intuitive - you just believe so as a product of your
training.

OK, so how would you teach use of a CDI to a brand new pilot?


--------------------
Richard Kaplan

www.flyimc.com