timed approaches/ ndb's

[brianjohn]

I am having trouble teaching an instrument student ndb approaches, and am trying to figure something out about "timed" approaches. They seem to be confusing.
Anyway, about timed approaches... the rules stipulate that if "one or more missed approach procedure is available, none require a course reversal." Ok... "If only one missed approach is available, a course reversal is not required."
Ok... Why not save ink and headache and just say "On a timed approach from a holding fix, no course reversal is required." Or am I missing something? It seems confusing.
About an ndb approach... (It has been so long for me doing this that I need to refresh)
Your procedure turn inbound on an ndb approach. Since the head of the adf needle always points to the sation, you turn TOWARDS the head to get on course if you drift. But what about after station passage and you are tracking AWAY from the ndb? If you are right of course, then the needle will point over your left shoulder. But what about if you have some left crosswind correction in there, and the needle points over your left shoulder. You really have no way of knowing if you are right or left of course. So how do you figure it out? Is this why it is imperative that after station passage you immediately turn to your inbound heading?
Any help is appreciated.

 

[brianjohn]

Ooops. I just realized I put this in the wrong forum.

 

[avbug]

Brian,

Flying inbound to an NDB, you can watch the pointy end of your indicator (some call the "head"), as it's supposed to be pointing in the general direction of the beacon. As you pass the beacon, the pointy end follows the beacon, and points behind you.

If you're using a fixed card compass you have a little math, if you really want to be creative...but nothing has changed for you, really. If before you were noting a specific number of degrees right or left of the top of the instrument to calculate your course using the "head," now you do the same thing using the "tail," because that's what's at the top of the instrument.

Some folks make it too difficult. Rather than trying to calculate degrees you can figure pencil eraser widths from the zero mark at the top of the instrument. Or fingers, or whatever. If you're on the inbound heading and the needle is pointing left of the zero at the top of the fixed card compass ADF navhead, then you're right of course. Correct left. If you just correct enough to put the needle straight up, then you're homing, and pointing at the station. Correct left some more, put the needle a pencil eraser width to the right of the top of the instrument.

Hold that until you drift back on course. When it's two pencil eraser widths to the right, you're on course. Turn back to the right...the needle should then be about one pencil eraser width to the right. Hold that for a while and see what you see. Sometimes, often, you may need a lot more correction, especially if you don't have very far to go, or the wind is very strong.

If you have a RMI/rotating card compass you can set to heading, you'll always have instant bearing information by seeing where the needle lies; it instantly shows you the bearing.

The ADF is probably the most simple and straight forward navigational instrument that can be put in the cockpit,and understanding it does wonders for understanding and being situationally aware in other more "modern" navigational displays and systems. It's biggest weakness, with respect to navigation, is that people make it too hard, complicate it too much.

 

[Vector4fun]

Brian,


I'll try to tackle the timed approach question. First of all, is anybody still doing those things??? I mean, 20 years ago, I ran some at a non-radar approach control I worked, but I think I heard there are only one or two non-radar approach controls left in the U.S., and I don't know where they are. I don't know if there are any Center controllers comfortable enuf with the procedures to try 'em.

Anyway, here's the first few paragraphs on Timed Approaches from the ATC Handbook, 7110.65:

6-7-1. APPLICATION
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Timed approaches using either nonradar procedures or radar vectors to the final approach course may be used at airports served by a tower if the following conditions are met:
​

NOTE-
These procedures require NAVAIDs and standard/special instrument approach procedures or adequate radar coverage which permit an aircraft to:

1. Hold at a fix located on the approach course or to be radar vectored to the final approach course for a straight-in approach in accordance with the minima specified in
para 6-7-5, Interval Minima.

2. Proceed in the direction of the airport along the approach course crossing the holding/approach fix at a specified altitude if required.

3. Continue descent for an approach to destination airport.
​

a. Direct communication is maintained with the aircraft until the pilot is instructed to contact the tower.
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b. If more than one missed approach procedure is available, none require course reversal.
​

c. If only one missed approach procedure is available, the following conditions are met:
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1. Course reversal is not required.
​

2. Reported ceiling and visibility are equal to or greater than the highest prescribed circling minimums for the instrument approach procedure in use.​

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You can read the entire section at:​

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http://www.faa.gov/ATpubs/ATC/Chp6/atc0607.html​

​

Anyway, you'll note that there are TWO requirements if only one missed approach is available. No course reversal, and WX has to be above highest circling minima. That's because with timed approaches, ATC needs approved non-radar separation for a possible missed approach. If only one missed approach is available, and two go missed that close together, there's no approved separation at the moment the second goes miss. Therefore, there has to be reasonable assurance that two aircraft won't miss the approach.​

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Obviously, the missed approach can't involve a course reversal, because the next aircraft on approach is right behind.​

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The Govt is not known for being concise in writing the regs...​