G'day people,

I have been greatly confused by this question:

Refer to ERC L6.
"You are tracking from Broome to Fitzroy Crossing. If your VOR is tuned to Curtin, the settings and indications which would confirm that you were abeam Curtin would be -
1 VOR OBS set to 002, CDI centred, flag showing TO
2 VOR OBS set to 182, CDI centred, flag showing TO
3 VOR OBS set to 092, CDI full scale deflection left, flag showing TO
4 VOR OBS set to 271, CDI full scale deflection right, flag showing FROM"

Below is a rough drawing of the situation for those who don't have ERC L6 in front of them. Now, I chose 2. My reasoning is that I thought to get the flag showing TO with the VOR in command sense, you have to set the reciprocal of your track under the OBS, as in this case you're actually on the 182 radial, tracking 002 degrees. The correct answer was given as 1. Could someone please explain this to me? Thank you!

Cheers,

Dan

Hi Dan,
The trick to this one is the TO flag.
As we know, the radials are radiating out from the station, which is how we find our postion in relation from them.
When we track on a radial. We can think of it as a straight 'highway' through the station from one side to the other. You take the highway you have selected on the OBS TO the station and continue on your merry way along the highway FROM the station. Command sense.

In this question, you are south of the aid. With 182 set on the OBS, the command sense indication would give you a FROM flag. In other words. You have already passed through the station and are now on your merry way travelling FROM it.
For answer 2 to work with a TO flag, you would have to be north of the aid.

For everyones benefit, lets look at whats wrong with answers 3 and 4.
First, they're parallel to our track and we couldn't use those radials for position fixing because they are way outside of the less than 45° intersecting lines.
Also. You wouldn't get a TO or FROM flag. Just a NAV or OFF flag because the navaid thinks you are getting station passage.

Hope this helps.

Cheers,
Mister W.

Hi Mister W,

That makes a lot of sense. So keeping it simple, using the 000 and 180 radials, if you were south tracking north you would dial 000 and if you were north tracking south, you would dial 180. So is it fair to say then, that to get command indications on a specific radial, you always set your current heading (disregarding if there is a wind at this point) under the OBS?

Cheers,

Dan

You know, sometimes I wish I could find the guy who invented the word 'radial' and kick his bum. As far as the pilot in flight is concerned, you simply set the track you intend to fly [what ever's written on your flight plan] on the OBS and the instrument will automatically tell you if that track will take you TO or FROM the station. The only time a pilot is concerned with a radial is when he/she is talking to ATC or to another pilot.

Great! Thanks, Bob.

Also, just confirming the only indication of station passage is the flag will change from TO to FROM or vice versa?

It will always change from TO to FROM unless you're in a helicopter and flying backwards! Then it would change from FROM to TO.

Not a helicopter pilot.... Yet!

I've got to wait until you finish your set of rotary books!

Cheers Bob