IFR Lesson 6: NDB intercepts in the sim

I’ve really fallen behind with my postings here, but my daughter got sick last week and took both her mom and I out of commission with her, so it has taken me a few days to recover and get around to updating my blog.

Last Tuesday I spent some time working on NDBs in the simulator.  Nick said he prefers the sim for this simply because he can move me around (in the virtual airplane) much more easily to simulate various NDB intercept scenarios.  Before we hoped in, or should I say logged on, we spent some time talking about the intercept procedures for NDBs.  He explained the method(s) of transferring the needle from the ADF to the HI, and using it to determine your intercept heading.  These procedures assume you are using a fixed card ADF, and there are other ways to do this, but I won’t go into them here and now.  So, here is what I learned is school today…

To calculate your intercept bearing TO the station, note the following in this order on the HI.

Desired Track – What bearing TO the station do you wish to fly.
Head of the needle – Transfer the needle to the HI
Intercept Heading – In the same direction that the needles is from the desired track, determine the appropriate intercept.

For example, if I want to fly a bearing of 030° TO the station, I first turn to a heading of 030° on the HI.  Now suppose the needle on the ADF is now showing a Relative Bearing (RB) of 40° degrees to the right.  If I now mentally transfer the needle from the ADF to the HI, it would be to the right of the current heading and indicate a heading of 070° degrees to the station.  I if then move to the right on the HI card once again, the same amount, which in this case is 40, I find that my intercept heading should be 110°.  All I have to do is then turn right to 110° and fly until the needle on the ADF falls to a 40° to a 80° RB to the left (or points to 030° when tranferred to the HI).  Once it does, I turn left to a heading of 030° and I should find that the head of the needle now points to 360°. (is vertical).

Clear as mud?  It’s hard to describe this without pictures, but trust me it works.

The procedure for intercepting bearings FROM the station is similar, but slightly different in that the order changes.  Again, note the following in this order on the HI.

Tail of the Needle – Transfer the needle from the ADF to the HI.
Desired Track – What bearing FROM the station do you wish to fly.
Intercept – In the same direction that the desired track is from the needle, determine the appropriate intercept.

For example, suppose I wanted to fly 270° FROM the station.  First I would turn to a heading of 270°, then once stabilzed on heading, I would mentally transfer the needle of the ADF to the HI.  In this case, let’s imagine the tail of this imaginary transferred needle points to 235° on the HI.  Starting at the tail or 235°, I move to my desired track of 270°, which is to the right of 235° on the HI.  The difference between 235° and 270° being 35°, I then continue to the right another 35 on the HI from my desired track of 270° to my intercept of 305° (or double the RB).  I should then turn right to 305° and fly until the tail of the needle on the ADF rises 35° to the left of my heading (or points to 270° when trasferred to the HI).  Once it does, I turn left to a heading of 270° and the tail of the needle should be pointed at 360°, indicating that the station is directly behind us and we are flying a bearing of 270° from the station. 

You might have noticed this but; when intercepting bearings TO the station, the needle always falls, while when intercepting bearings from the Station the needle (tail) always rises.

All of this logic is well and good but throw me behind the panel, or in this case the monitor, and I sometimes go instantly stupid.  I did OK, but to be honest, I don’t really care for NDBs and I sometimes found it challenging to do all these needled transferring exercises while flying the plane (sim).  I would often get myself set up on an intercept, only to forget what RB I was then looking for on the ADF.  I must have flown a dozen or so intercept exercises with limited success, when Nick threw a good stiff crosswind at me…. Argh, NDBs suck!   One thing is for sure, my VOR skills are a lot stronger than my NDB skills.  Oh well, practice, practice, practice.

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© Brad Oliver and PilotBrad.com, 2009. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Brad Oliver and PilotBrad.com with appropriate and specific direction to the original content.

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