to HSI or not to HSI

"Michael" wrote in message
om...
Dave Butler wrote
If we install the HSI, the no-longer-used CDI hole can be used for the
electric
AI that's been waaaay over on the other side of the panel.

Actually, if your primary AI is vacuum and the secondary is electric,
you can simply remove the T&B and install the second AI in its place.
AC91-75 permits the replacement of the T&B with a second AI, as long
as the power source for the 2nd AI is different from the power source
for the 1st AI. So really, being able to free up the hole should not
factor into your decision.

Some people love HSI's, some hate them, some are indifferent. I've
flown several planes with HSI's and I'm indifferent. It's OK. A DG
with CDI is also OK. About the only time an HSI really has an
advantage is when you're flying reverse course on a localizer. Other
than in training, I do not believe I have ever had to do that.

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


Michael

In article ,
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?

An HSI is like a CDI you can spin around. When shooting a back course
it is effectively upside down, cancelling out the reverse sensing.

--
Ben Jackson

http://www.ben.com/

"Ben Jackson" wrote in message
news:mkXkd.397609$D%.109302@attbi_s51...
In article ,
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?

An HSI is like a CDI you can spin around. When shooting a back course
it is effectively upside down, cancelling out the reverse sensing.

Yes, thanks.
But there is no such thing as "reverse-sensing" on the localizer. If
perhaps the current common teaching of localizers and CDI was corrected then
we that selling point of HSI is dropped.

The CDI needle points to the color sector you are in. On some (older) nav
heads the blue and yellow sectors were indicated. So, no need to look for
reverse sensing/etc, just look at the approach chart, look at the needle and
you will know where you are relative to the course. Nothing could be
simpler.


--
Ben Jackson

http://www.ben.com/

"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.

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.

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.

Michael

"Michael" wrote in message
om...

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).

I have such a switch on my airplane -- it is part of my Cessna 400B
autopilot control head. Just flip the switch and the CDI needle reverses
its orientation.

I agree completely that this makes a back course approach easier to fly even
though "training" should be able to solve the problem otherwise.

Let me give another example to support your point. One of the most
challenging situations I occasionally try in my simulator is a demonstration
of reversed ailerons not caught by a pilot on preflight. In theory, once
the pilot realizes what happened, there is no emergency at all -- the
airplane is perfectly controllable. In reality, almost all pilots find this
to be an extremely difficult scenario, and in fact it seems as if the
higher-time the pilot the harder it is to reverse one's thinking and provide
reverse aileron input. The same is likely true when flying a localizer
back-course approach; we are all so used to "normal" sensing on a CDI needle
that our responses become so ingrained/automatic as to make it much harder
to reverse this action on rare back-course approach.

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

www.flyimc.com

Once one accepts the fact that all sensing is "normal", and flies
headings as indicated by the VOR head, instead of the more difficult
methd of flying left and right needles, back course localizer flying
is no more difficult than "ordinary" course tracking.

On Sat, 13 Nov 2004 21:07:48 -0500, "Richard Kaplan"
wrote:


"Michael" wrote in message
. com...

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).

I have such a switch on my airplane -- it is part of my Cessna 400B
autopilot control head. Just flip the switch and the CDI needle reverses
its orientation.

I agree completely that this makes a back course approach easier to fly even
though "training" should be able to solve the problem otherwise.

Let me give another example to support your point. One of the most
challenging situations I occasionally try in my simulator is a demonstration
of reversed ailerons not caught by a pilot on preflight. In theory, once
the pilot realizes what happened, there is no emergency at all -- the
airplane is perfectly controllable. In reality, almost all pilots find this
to be an extremely difficult scenario, and in fact it seems as if the
higher-time the pilot the harder it is to reverse one's thinking and provide
reverse aileron input. The same is likely true when flying a localizer
back-course approach; we are all so used to "normal" sensing on a CDI needle
that our responses become so ingrained/automatic as to make it much harder
to reverse this action on rare back-course approach.

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

www.flyimc.com


d

Once one accepts the fact that all sensing is "normal", and flies
headings as indicated by the VOR head, instead of the more difficult
methd of flying left and right needles, back course localizer flying
is no more difficult than "ordinary" course tracking.

Any way you look at it -- left/right, to/from, yellow/blue -- a backcourse
approach is not a common situation and human nature is such that this means
there is more likelihood for error.


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

www.flyimc.com

Agreed.

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


On Sun, 14 Nov 2004 01:51:32 -0500, "Richard Kaplan"
wrote:


Once one accepts the fact that all sensing is "normal", and flies
headings as indicated by the VOR head, instead of the more difficult
methd of flying left and right needles, back course localizer flying
is no more difficult than "ordinary" course tracking.

Any way you look at it -- left/right, to/from, yellow/blue -- a backcourse
approach is not a common situation and human nature is such that this means
there is more likelihood for error.


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

www.flyimc.com

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".

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.


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

www.flyimc.com

"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