NDB approaches -- what are they good for?

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/