How wide is an NDB approach course?

Andrey Serbinenko wrote:
I believe the unsafe aspect of the system is the lack of training in
modern curriculums and our lack of practice with the equipment.

This reminded me of a useful training aid that I've put together
some time ago. It is a known fact that any AM radio station can
serve as a radio beacon that an ADF can be tuned to. AM radio
stations are everywhere, unlike real NDB transmitters, and they are
just as good for practicing NDB work as any NDB. So, I have
downloaded a list of AM-transmitting antenna from FCC, along with
their lat/lon, callsign, and output power, and transformed it into
a google-earth file. Then I zoomed-in on the area of my interest
in google-earth, and printed the map with the stations. Very handy
for NDB practice. Here's a link to the google-earth file containing
all AM-transmitting antenna within 1000km radius of NYC:
http://tinyurl.com/35rdez
If anyone wants such a file for some other part of the US, just let
me know, and I'll generate it and put it online.

The only problem I have with trying to use a MW AM radio station for
navigation is that they don't have consistent power and radiation
patterns. Typically they'll broadcast a reasonably strong signal during
the day. However at night, because the ionospheric absorption goes down
and because the signal can skip, the FCC requires most stations to dial
their power back and change antenna patterns.

This can result in a sudden loss of signal when the sun sets. I would
advise anyone looking for NDB practice to avoid the evening hours, and
not to navigate with AM stations in actual IMC conditions unless you're
very familiar with the radiation pattern and power output of the station
you're using. Remember, AM radio stations no longer report service
outages via NOTAM, so you're pretty much on your own here.

Jake Brodsky

Jake Brodsky wrote:
Andrey Serbinenko wrote:

I believe the unsafe aspect of the system is the lack of training in
modern curriculums and our lack of practice with the equipment.


This reminded me of a useful training aid that I've put together
some time ago. It is a known fact that any AM radio station can
serve as a radio beacon that an ADF can be tuned to. AM radio
stations are everywhere, unlike real NDB transmitters, and they are
just as good for practicing NDB work as any NDB. So, I have
downloaded a list of AM-transmitting antenna from FCC, along with
their lat/lon, callsign, and output power, and transformed it into
a google-earth file. Then I zoomed-in on the area of my interest
in google-earth, and printed the map with the stations. Very handy
for NDB practice. Here's a link to the google-earth file containing
all AM-transmitting antenna within 1000km radius of NYC:
http://tinyurl.com/35rdez
If anyone wants such a file for some other part of the US, just let
me know, and I'll generate it and put it online.


The only problem I have with trying to use a MW AM radio station for
navigation is that they don't have consistent power and radiation
patterns. Typically they'll broadcast a reasonably strong signal during
the day. However at night, because the ionospheric absorption goes down
and because the signal can skip, the FCC requires most stations to dial
their power back and change antenna patterns.

He clearly said for practice use, not for actual navigation. I actually
found the signal better from the radio station than from most NDBs,
but I definitely wouldn't depend on one for anything other than practice
with a safety pilot or instructor in VFR conditions.


Matt

The other nice thing is you could use the local AM radio for VFR
navigation into Podunk, and catch the hog report and find out what's on
sale at Burford's hardware too!!

Now of course it's useful to listen to ball games and give you a heads
up on the stadium TFR.

Mxsmanic wrote:
Matt Whiting writes:

That is pretty neat. Yes, I used 1490 in Wellsboro for practice at N38.
It isn't exctly aligned with the runway, but is close and we made up a
little home-made approach for practice. It worked well.

I think the NDB concept was deliberately designed with this in mind,
so that ordinary radio stations could be used for emergency navigation
in a pinch. The frequency range is the same as AM radio, and I hardly
think that a coincidence.

--
Transpose mxsmanic and gmail to reach me by e-mail.

-----Original Message-----

From: Mxsmanic ]

Posted At: Saturday, January 20, 2007 8:09 AM

Posted To: rec.aviation.ifr

Conversation: How wide is an NDB approach course?

Subject: How wide is an NDB approach course?



Matt Whiting writes:



That is pretty neat. Yes, I used 1490 in Wellsboro for practice at
N38.

It isn't exctly aligned with the runway, but is close and we made
up a

little home-made approach for practice. It worked well.



I think the NDB concept was deliberately designed with this in mind,

so that ordinary radio stations could be used for emergency navigation

in a pinch. The frequency range is the same as AM radio, and I hardly

think that a coincidence.



--

Transpose mxsmanic and gmail to reach me by e-mail.



Think back even further to the low frequency radio ranges. This is the
bottom range on the old Bendix coffee grinder ADFs. The LF signal could
be "heard" over an extraordinarily long distance with relatively low
power. LF was around for navigation before AM radio really found its way
into aircraft. From Wikipedia:



"These radio aids became the navigation resource for enroute airways
flying in clear and clouded weather, and for airport letdown approach
patterns in limited ceiling and visibility conditions. Fixed emplacement
of low frequency, non-directional radio beacons came into use as
distance checkpoints along airways and along airport approach patterns.
Many, but not all of these low frequency systems were superseded after
World War II by higher frequency (hundreds of megacycles instead of
hundreds of kilocycles) radio wave emitting installations known as
"omni-range" and "localizer" facilities. This changeover to higher
frequency constituted an advance in degree but not in kind."

Jake Brodsky writes:

Remember, AM radio stations no longer report service
outages via NOTAM, so you're pretty much on your own here.

Are you saying that they did this at one time in the past?

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic wrote:
Jake Brodsky writes:

Remember, AM radio stations no longer report service
outages via NOTAM, so you're pretty much on your own here.

Are you saying that they did this at one time in the past?

I seem to recall that *charted* stations were NOTAMed when they went out
of service. However, I am not entirely sure about this.

Jake Brodsky

Bill Zaleski wrote:
On Tue, 16 Jan 2007 16:50:04 -0800, Sam Spade
wrote:


Bill Zaleski wrote:

On Tue, 16 Jan 2007 21:28:12 GMT, Jose
wrote:



What is the protected area under an NDB approach course? Since the
course guidance is cruder than an ILS, I'd expect it would be wider, but
how much wider? I ask also in the context of when I should consider
myself "established" on course (for purposes of descent).

Jose


When within 10 degrees of the published course.


There is no policy or rule to support that.


He asked when he should consider himself established for the purpose
of descent. Have you got better guideline to follow when in a cockpit
looking at an instrument panel? In the absence of policy or rules, as
you say, what do you suggest a better answer would be?


When the bearing indicates on-course. 10 degrees is way too early.

Jose wrote:

[You're established inbound on an NDB] When within 10 degrees of the
published course.

There is no policy or rule to support that.


Taking Sam Spade's TERPs quote,

The primary area is longitudinally centered on the FAC, and is 10
miles long. The primary area is 2.5 miles wide at the facility, and
expands uniformly to 6 miles wide at 10 miles from the facility.


I draw a little diagram, and find that the angle along the outside of
the primary area to be atan(((6/2)-(2.5/2))/10) = atan(7/40) = 10
degrees. So, ten degrees from the facility puts me 2.5 miles inside the
protected area. Sounds good to me. Start on down.

Jose
That is right at the limits without any compass or ADF error. Not a
good idea. But, it's your call

Robert M. Gary wrote:

Jose wrote:

What is the protected area under an NDB approach course? Since the
course guidance is cruder than an ILS, I'd expect it would be wider, but
how much wider? I ask also in the context of when I should consider
myself "established" on course (for purposes of descent).


If, when reaching the MAP, you are in the same city as the airport you
count yourself luck.

-Robert


With an RMI you might be somewhere in town. With a fixed card you might
not even be in the same county.

-----Original Message-----
From: Sam Spade ]
Posted At: Saturday, January 20, 2007 6:46 PM
Posted To: rec.aviation.ifr
Conversation: How wide is an NDB approach course?
Subject: How wide is an NDB approach course?

....

With an RMI you might be somewhere in town. With a fixed card you
might
not even be in the same county.

Come on now Sam, you know that's not right. NDB approaches are safe and
accurate when properly executed by trained and current pilots. They have
been for years. I will grant that they take a lot more situational
awareness than letting the GPS steer the bird down the tracks, but even
so the NDB approach still works just fine.