How wide is an NDB approach course?

On Wed, 17 Jan 2007 04:57:04 GMT, 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's a lot of math to try to acomplish during an NDB approach.
Sounds like you are measuring it with a micrometer and cutting it with
an axe. You need much simpler personal guidelines when you take this
stuff into the cockpit.

That's a lot of math to try to acomplish during an NDB approach.
Sounds like you are measuring it with a micrometer and cutting it with
an axe. You need much simpler personal guidelines when you take this
stuff into the cockpit.

I don't accomplish this math during an NDB approach. I accomplish it
here, once, on the ground. Now I have a rule-of-thumb (established at
10 degrees) to carry with me on all NDB approaches.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Within 10deg is pretty simple guidance in my book!

Bill Zaleski wrote:
On Wed, 17 Jan 2007 04:57:04 GMT, 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's a lot of math to try to acomplish during an NDB approach.
Sounds like you are measuring it with a micrometer and cutting it with
an axe. You need much simpler personal guidelines when you take this
stuff into the cockpit.

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

Sam Spade wrote:
When within 10 degrees of the published course.
There is no policy or rule to support that.

Yeah, the FAA is so incredibly disfunctional that it is literally
possible to have a 'properly' (meaning in accordance with TERPS)
designed approach flown 'correctly' (meaning to the level required to
pass the instrument rating ride as per the PTS) with functional
(meaning working well enough to pass the mandated operational checks)
equipment, and still slam yourself into something.

Check out the LVJ VOR-B.

Michael

Michael wrote:

Sam Spade wrote:

When within 10 degrees of the published course.

There is no policy or rule to support that.


Yeah, the FAA is so incredibly disfunctional that it is literally
possible to have a 'properly' (meaning in accordance with TERPS)
designed approach flown 'correctly' (meaning to the level required to
pass the instrument rating ride as per the PTS) with functional
(meaning working well enough to pass the mandated operational checks)
equipment, and still slam yourself into something.

Check out the LVJ VOR-B.

Michael


What's wrong with that approach, at least until leaving MDA?

If you're referring to the snake pit below MDA when circle-to-land only
minima are published, this one is a comparative cakewalk compared to the
high HAA circling MDAs in the mountains.

Sam Spade wrote:
What's wrong with that approach, at least until leaving MDA?

The 1200 ft tower that you can hit. It's located outside the trapezium
that defines the protected areas (inner and outer) but your VOR
receiver can be within 4 degrees of perfect (the more restrictive
standard for the VOR check - some COR checks allow 6 degrees) and your
needle need not exceed 3/4 scale deflection (the more restrictive
standard on the instrument airplane PTS - you are allowed full scale on
the partial panel approach) to put you right into the tower.

Michael

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

A whole lot wider than an ILS. From TERPs.

b. Area. Figure 57 illustrates the final approach primary and secondary
areas. 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. A
secondary area is on each side of the primary area. It is zero miles
wide at the facility, and expands uniformly to 1.34 miles on each side
of the primary area at 10 miles from the facility. When the 5 mile PT is
used, only the inner 5 miles of the final approach area need be considered.

The required obstacle clearance is also greater than other non-precision
approaches: 300 feet with FAF, 350 without.

The FAA does not define when established on an NDB or any other course.
It is implied by the IR PTS, but that is not a precise definition.

ICAO does define such things. But, those are not valid for FAA procedures.

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

From TERPs:

b. Area. Figure 57 illustrates the final approach primary and secondary
areas. 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. A
secondary area is on each side of the primary area. It is zero miles
wide at the facility, and expands uniformly to 1.34 miles on each side
of the primary area at 10 miles from the facility. When the 5 mile PT is
used, only the inner 5 miles of the final approach area need be considered.

Also, the minimum obstacle clearance is greater than other NPAs; 300
feet with FAF, 350 without.

The FAA has never defined on course. That is up to the pilot. The IR
PTS gives some fences, but that is about it.

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