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CPL question: TACAN

PostPosted:Fri Jan 08, 2021 11:59 am
by NDB_hold
One of the questions in my Radio Nav CPL exam which I failed earlier this week was I think misleading and I am wondering whether to follow it up. (Although I’d need 2 more right answers to pass!)

Picture showed the Linton-on-Ouse TACAN on a civilian chart showing the frequency of 109.0MHz. The questions was something like:

What information would you expect to receive if you tuned frequency 109.0MHz on your VHF Nav radio?

The 2 plausible options were:

Slant range
Nothing, because it is military equipment

I answered the second but put a comment in the box that this was misleading, as the reason is actually that it’s on UHF.

But the first is wrong, because you would only receive DME if you put that frequency in your DME receiver or had a remote DME tuning option on the box - and the question didn’t say you did.

Was I right?

Re: CPL question: TACAN

PostPosted:Fri Jan 08, 2021 12:19 pm
by David Wood
You will pick up Slant Range (ie, as if the beacon is a DME) but nothing else. You are correct that you would only get the range if the correct frequency was put into the DME unit. However, what they might be getting at is that the DME unit could and often is slaved to your Nav radio - although the question should really make that clear because if it isn't you'll get nowt.

Re: CPL question: TACAN

PostPosted:Fri Jan 08, 2021 12:36 pm
by NDB_hold
Yes, that’s my point really. I instantly went for 'slant range', then reread the question and decided it might be a trick.

Re: CPL question: TACAN

PostPosted:Thu Jan 14, 2021 11:49 am
by 2Donkeys
The question is poorly worded for all the reasons you suggest @NDB_hold.

TACAN will respond like a DME (which we know is slant range) if the DME is tuned to the equivalent paired VHF frequency. The Nav Radio will not in and of itself provide any information if tuned to the TACAN frequency.

Re: CPL question: TACAN

PostPosted:Thu Jan 14, 2021 11:56 am
by johnm
Who writes this drivel??

I remember my own fury at the bloody nonsense I had to absorb to get through my IR exams. I then promptly forgot it all and went off and learned what I really needed to know :roll: