NDB approaches -- what are they good for?

David Megginson wrote
I think that the only way that a LOC or VOR approach would be
significantly easier than an NDB approach is if you were chasing the
needle: if you chase the CDI in a VOR or LOC approach, you still stay
close to track (in a constant series of S-turns); if you chase the NDB
needle, you end up approaching the NDB downwind from the track.

You got it. The other difference - with the NDB, you absolutely must
keep the DG (if available) on the correct compass heading.

I'm not nearly good enough to do a lot of mental math on any approach
(not as long as they maintain that picky requirement about not flying
into the ground), so I just leave my ADF card with north at the top
like a fixed card, and remember how far my wind-correction angle is to
the left or right, just like I do with a VOR or LOC approach. As long
as the NDB needle position is the same as my wind-correction angle,
I'm on the approach track.

How about when you're doing the procedure turn? How do you know when
to start your turn to your final approach course? More mental math?

The only difference is the fact that the ADF starts (sort-of)
reverse-sensing after station passage, so that what starts out like a
LOC approach can end up like a LOC(BC) approach. I just remember

Push the head, pull the tail

and everything usually works out fine.

More stuff to remember. The VOR needle keeps working the same way
throughout the approach.

You can teach those skills without the ADF, but without the ADF you
can get by with NOT teaching those skills, save 10 hours, and the
student can still pass the checkride.

I find it hard to believe that anyone could pass an IFR checkride by
chasing a CDI in a zigzag -- can they?

Yes. They can. I've seen it happen. Just like students who drive
the airplane onto the runway can pass the private checkride in a 172
or Cherokee, when a Cub or a Champ would eat their lunch for doing it.
I've seen that happen too.

Like I said - you don't need an ADF to teach these basic skills - and
they are basic - but without the ADF, you can get by without teaching
them, and many do.

Michael

(Michael) writes:

How about when you're doing the procedure turn? How do you know when
to start your turn to your final approach course? More mental math?

There are big marks on the ADF indicator every 45 degrees, just as
there are on the HI. Depending on which side I'm coming in from the
PT, I wait until the needle is close to the 45-degree mark to the left
or right of the top of the indicator, then turn in.

The inbound turn is actually one of the few places where the NDB
approach is easier -- the LOC sometimes comes across so fast that my
inbound turn from the PT becomes an S-turn, especially if I have a
tailwind (i.e. a crosswind for the final approach). The ADF always
gives me lots of warning as I approach the track and never forces me
to snap into a 30-degree bank just to stay within the protected area.

I hope that there aren't any instructors who force students to do
complex mental math for this kind of thing instead of just using the
big, easy marks on the ADF indicator. If instructors do that, no
wonder people hate NDB approaches so much!

More stuff to remember. The VOR needle keeps working the same way
throughout the approach.

Quite right. As someone else mentioned, though, the LOC(BC) approach
can be even more of a challenge. Not only do you have the reverse
sensing, which can be a big problem if you don't have special
equipment and you're not current with LOC(BC) approaches, but you also
have the exaggerated sensitivity near the threshold approach, at
exactly the time that you don't want to destabilize your approach by
chasing a wandering CDI.

I find it hard to believe that anyone could pass an IFR checkride by
chasing a CDI in a zigzag -- can they?

Yes. They can. I've seen it happen.

OK, now I see what you mean about the NDB approaches forcing
instructors to teach basic skills that they might otherwise neglect.
I don't particularly like that argument -- it's the same as the flawed
argument that teaching Latin helps people learn English grammar -- but
at least I can see where you're coming from. Perhaps raising the test
standards in that area would be a better solution.

For me, finishing up my instrument rating in Eastern Ontario, NDB
approaches and enroute navigation along LF/MF airways are simply a
fact of life and will likely be so for a while after my flight test.
I make no claim that NDB approaches are especially virtuous or make me
a better pilot, but the alternative (an IFR-certified GPS) is
prohibitively expensive -- a whole year's flying expenses for my
Warrior II -- and even then, it wouldn't let me fly IFR in much of the
far north.


All the best,


David

--
David Megginson, , http://www.megginson.com/

David Megginson wrote:


There are big marks on the ADF indicator every 45 degrees, just as
there are on the HI. Depending on which side I'm coming in from the
PT, I wait until the needle is close to the 45-degree mark to the left
or right of the top of the indicator, then turn in.

Laugh It took me a while to figure out what you meant by this. My mental
picture of the process is sufficiently different from yours that I'd no
idea from where you were getting the number 45. It finally dawned on me
that you're flying a 45 degree intercept to the inbound course.

I know when to turn because the ADF is telling me that I'm close to the
desired inbound course. I tend to do this by mentally overlaying the
picture of the HI with the picture of the ADF, but I'll turn the card if I
think of it.

It never occurred to me to see it as you do, although of course we're doing
precisely the same thing.

The inbound turn is actually one of the few places where the NDB
approach is easier -- the LOC sometimes comes across so fast that my
inbound turn from the PT becomes an S-turn, especially if I have a
tailwind (i.e. a crosswind for the final approach). The ADF always
gives me lots of warning as I approach the track and never forces me
to snap into a 30-degree bank just to stay within the protected area.

For this reason, why not a 30 degree intercept to a localizer? It slows the
needle.

- Andrew

Andrew Gideon writes:

Laugh It took me a while to figure out what you meant by this. My
mental picture of the process is sufficiently different from yours
that I'd no idea from where you were getting the number 45. It
finally dawned on me that you're flying a 45 degree intercept to the
inbound course.

Sorry -- I was assuming the standard, hockey-stick procedure turn, and
should have said that.

For this reason, why not a 30 degree intercept to a localizer? It
slows the needle.

Sure, that would work fine, and would have the advantage of giving me
a longer final. I use 45 only because I can read the headings
straight off the procedure-turn diagrams on the approach plates, so I
don't have to think too much. I love aviation-arithmetic problems
sitting here at my desk, but my head gets a little mushy in the plane
sometimes.


All the best,


David

--
David Megginson, , http://www.megginson.com/

David Megginson wrote
OK, now I see what you mean about the NDB approaches forcing
instructors to teach basic skills that they might otherwise neglect.

Like I said, you don't need the ADF to teach those things. On the
other hand, without the ADF, you can get by without teaching them. I
don't believe that's a good enough reason to put an ADF in every
instrument trainer - you'll recall I was the one who proposed an
instrument rating not valid for ADF approaches as the solution for
those who didn't learn the necessary skills. It's the same solution
used for taildraggers, and I think it works OK.

Perhaps raising the test
standards in that area would be a better solution.

Maybe. Or maybe in the modern world we just don't need to force
people to learn those basic skills. Look at how many pilots fly just
fine for years without really learning to use the rudder or make full
stall landings. Those things are not tremendously relevant in today's
trainers (C-172's and Cherokees) under most conditions, and they're
REALLY not relevant in today's transport category airplanes. Thus I
can easily see why one of those career-track programs wouldn't bother
teaching those skills.

The same applies to the ADF. For this reason, a lot of the
career-track operations just don't have ADF's in any of their
airplanes. And that's fine. My real goal with the ADF limitation is
to make it impossible for the graduates of those programs (who are all
CFII's) to teach IFR in the world of light GA, where the NDB approach
is alive and well, without being forced to develop those basic skills.

Michael

(Michael) writes:

Look at how many pilots fly just fine for years without really
learning to use the rudder or make full stall landings.

Doesn't loss of control on the landing roll account for a
disproportionately large number of accidents, even for Cherokees and
Skyhawks?


All the best,


David

--
David Megginson, , http://www.megginson.com/

David Megginson wrote
Doesn't loss of control on the landing roll account for a
disproportionately large number of accidents, even for Cherokees and
Skyhawks?

Disproportionately large? I don't know about that. I know there are
VERY few fatal landing accidents.

Michael

In article , David Megginson
writes:

Look at how many pilots fly just fine for years without really
learning to use the rudder or make full stall landings.

Doesn't loss of control on the landing roll account for a
disproportionately large number of accidents, even for Cherokees and
Skyhawks?

When learning to fly a sailplane in Tucson, the instructor commented that the
A10 pilots that came up from Davis Monthan AF thought that the rudder pedals
were welded to the floor. With a sailplane you sure get adverse yaw and need
rudder.

Chuck

(PaulaJay1) writes:

When learning to fly a sailplane in Tucson, the instructor commented
that the A10 pilots that came up from Davis Monthan AF thought that
the rudder pedals were welded to the floor. With a sailplane you
sure get adverse yaw and need rudder.

Even in a docile Cherokee or Skyhawk, you still need to use those
rudder pedals in the air during initial climbout and (especially)
during a crosswind landing.


All the best,


David

--
David Megginson, , http://www.megginson.com/

Michael wrote:

David Megginson wrote
I think that the only way that a LOC or VOR approach would be
significantly easier than an NDB approach is if you were chasing the
needle: if you chase the CDI in a VOR or LOC approach, you still stay
close to track (in a constant series of S-turns); if you chase the NDB
needle, you end up approaching the NDB downwind from the track.

You got it. The other difference - with the NDB, you absolutely must
keep the DG (if available) on the correct compass heading.

I'm getting a mental picture of someone unfamiliar with how the ADF works
trying to fly an NDB approach traveling forever in circles around the
beacon.

- Andrew