NDB Chart Question

[ryanbatc]

Ok dokie - no need to discuss NDB's vs GPS (lol) but I have question regarding this NDB approach into Oconto, WI

http://naco.faa.gov/d-tpp/1003/06337NG29.PDF

What I have for equipment is an HSI and an ADF indicator with a moveable card under it.

I started by trying to line up the card with my heading (from the hsi) but just got screwed up that way. So I left it where it was and imagined the needle overlayed onto my HSI. From the chart we see the final approach course (or bearing whatever its called) is 301. From my picture here I presume I'm slightly right of course? I'm heading 300-ish and if I were to imagine the adf needle on my HSI it would point at about a 295. How do I know what my deviation is off the final and how do I correct it? Do I turn toward the needle or away??? That's what confuses me the most. Also, when I'm flying outbound prior to reaching the PT, again, do I correct towards the needle or away?

Thanks for any help...

http://i141.photobucket.com/albums/r43/ryanbatc/ndbd.jpg

[Brett_Henderson]

NDB approaches are fun, and challenging :jump:

You've already lept the first hurdle, in that you've ignored the ADF compass card, and are mentally superimposing the needle onto your heading indicator (HSI in this case)..

First we'll clear up terminology (no vagueness allowed)...


From the chart we see the final approach course (or bearing whatever its called) is 301

COURSE = where you want to go
HEADING = is where the nose is pointing
TRACK = the path you actually ARE following
BEARING = is a magnetic direction to a specific point
RELATIVE BEARING = the direction to a specific point using your heading as zero

NOW.. we'll get into the nuances of an NDB approach. An ADF points to the NDB. That's all it does. Like, if you could slip a sectional-chart behind the ADF needle oriented so that the top of the chart matched your heading.. the needle would point to the NDB on the chart.

The only time it can give you accurate course guidance, is IF there was zero wind. We'll use you panel shot and describe what would be happening with zero wind.. and what could be happening with wind that was being accurately compensated for.

ZERO WIND: Your heading and track are both 300. The NDB is ahead of you, and slightly to the left. If you continued this track, you'd fly perfectly parallel to the inbound course, and pass to the right of the NDB. As you get nearer the NDB, the needle will move more to the left (and be at 9 o'clock as you passed the NDB).

What you want to do, is to be flying the inbound heading WHILE the ADF needle is at 12 o'clock. To accomplish this.. you'd turn left something like 20 degrees.. the needle will move to right of 12 o'clock.. hold that heading until your super-imposition of that needle onto the HSI is pointing at 300.. then turn to 300... Makes sense ?

NOW.. the tricky part. Let's assume that there is wind (there always is).. and let's pretend that it's out of north. In order to track the inbound course, you'd have to fly a slight crab.. This means that your heading will be right of 300.. but the the ADF needle will be on 300 (not at 12 o'clock). Your make heading changes to keep the ADF needle on an HSI super-imposed 300, even though it's rarely at 12 o'clock...

To illustrate this theory .. picture what would happen if you tried to fly straight north, to an NDB, by keeping the ADF needle at 12 o'clock with a wind out of the east.. Keeping the nose pointing at the NDB (needle at 12 o'clock) will have you fliyng a giant spiral-like arc.. and if the wind is strong enough, you'd be tracking nearly east-bound by the time you reach the NDB..

Edit: The outbound course is maintained by a mirror image. You'd fly a heading that keeps a super-imposed ADF needle on ~300. If the needle is right of 300 turn 20 degrees or so to the right.. wait for the super-imposition to reach 300.. and make heading corrections to keep it on 300 (not always 6 o'clock depending on wind)

[ryanbatc]

Ok thanks. It's something I don't do often but on occassion I try to do it with whatever weather is present (real world when I fly) so like you said 99.5% of the time there is indeed wind.

So I always correct towards the needle... It's sorta like a VOR I spose... but for some reason it's harder to get stuck in my brain.

[Brett_Henderson]

Try to picture it like this..

If you could rotate the gauge forward (so you had to look down at it).. the needle would be pointing to the beacon..


I did a flight-training series at a different forum.. part 5.1 of 7 describes flying to an NDB.. I'll PM the link.. feel free to read all parts and ask questions..