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## IREX VOR

• Posts: 21

### Don created the topic: IREX VOR

"You departed Dubbo at 0327 for Mudgee. Your VOR [tuned to Dubbo] has 101 set on the OBS. Your DME is also tuned to Dubbo. At time 0336, the CDI on your VOR is indicating two dots left of centre and the DME is indicating 28. Your heading of 105 degrees M has been constant since departure.

The track from Dubbo to Mudgee, as per ERC L 3 is 101 degrees

Thank you!
Don

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 703

### John.Heddles replied the topic: IREX VOR

I tell you the answer, you learn naught. I give you some clues, you get the answer and learn something along the way.

(a) ERC gives you the track Mudgee to Dubbo, which is ?

(b) ERC gives you the distance between the two, which is ?

(c) what is your track error at 0336 ?

(d) (quick mental arithmetic) what is the closing angle to Mudgee ?

(e) so what is the track to Mudgee from your present position ?

(g) so what is the angle between track to Mudgee and present heading ?

(h) and what is the ADF reading as a relative bearing ? (before you do any corrections)

Engineering specialist in aircraft performance and weight control.

• Posts: 21

### Don replied the topic: IREX VOR

Hi John,
Thank you very much for the steps. Answer is 352 degrees R.

But I have a little thing to clarify again, the question it says 2 dots left of the center, for this question I took it is as 4 degrees.
But Bob tait's IREX book, page # 65 - Question 14. Instrument indicate CDI is in 2 dots left, answer considered as 6 degrees. ( as far as I know 2 dots count including the circle in the VOR instrument)

Thank you very much for the steps again!
Don

• John.Heddles
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• Posts: 703

### John.Heddles replied the topic: IREX VOR

As you quite sure of that answer ? Perhaps you can post your working ?

the question it says 2 dots left of the center, for this question I took it is as 4 degrees.

I would have to dig out the relevant TSOs to see what the indicator presentation requirements are - bit out of my engineering discipline - black art stuff is E&I.

Pilot-wise, I am familiar with two presentations;

a small bullseye with 5 additional dots either side

and a large bullseye with 4 dots either side.

On the latter presentation, the bullseye ring is the first dot. Either way we figure 10 degrees FSD for a VOR. I haven't looked at Bob's IREX text so I can't comment on what it might say. No doubt either Bob or Stuart will comment if appropriate.

Engineering specialist in aircraft performance and weight control.

• Posts: 21

### Don replied the topic: IREX VOR

H +/- A = T
105 +/- A = 097 (doubling the TE)
+/- A = 097 - 105
= - 8 to (360 - 8 to)
= 352 degrees R
##### Attachments:

• John.Heddles
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• Posts: 703

### John.Heddles replied the topic: IREX VOR

Can I get you to recheck your 101 degrees against the ERC ?

Also, how far, as a fraction of the distance, have you gone at 0336 ?

(I'm very impressed by your arithmetic, even if I have absolutely no idea what it might mean ....)

Engineering specialist in aircraft performance and weight control.

• Posts: 21

### Don replied the topic: IREX VOR

Thank you very much for the prompt respond.
ERC - closer to Dubbo says 101. And also question is saying Your VOR set to Dubbo 101 on the OBS.
A/C is half way between. At 0336 A/C is 28 nm.

Find the attachment.
Many Thankx!
Don
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• John.Heddles
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• Posts: 703

### John.Heddles replied the topic: IREX VOR

Ref 101 degrees. I downloaded the current ERC (which could be different to yours if you have a superseded version). Can I get you to check the inbound track to MDG at the MDG end of the sector ? What is that track ?

Where I am going is to endeavour to show that the mental sequence to sort out this orientation problem is extremely straightforward and you really don't need to jump through a bunch of arithmetic tricks.

Engineering specialist in aircraft performance and weight control.

• Posts: 2312

### bobtait replied the topic: IREX VOR

John makes a valid point concerning the different VOR presentations. However I remember having this discussion with CASA some years ago and they said the question would use a phrase such as 'two dots left of the centre circle' so you could assume that the edge of the centre circle was the first 'dot'. I'm pretty sure that I've mentioned that somewhere in the book. I know that still doesn't account for the two presentations. We can only hope that the examiners have addressed the issue.

Bob