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ADF question

  • linc90
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linc90 created the topic: ADF question

Hi Bob, Richard
Exercise 11 on page 53 I understand question 1 and 2 but question 4 Im a but confused in the question were it asked what HDG to maintain after intercept, it says the answer is 155 my understanding if you put 155 that would make you fly more off track because you found yourself right of track. I would of thought you would subtract 15 from your HDG opposite to your FPT ? so that you would be pointing the nose into wind?

Sorry if this makes no sense

Cheers
Linc90
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Richard replied the topic: ADF question

Hi Linc,

This one has come up before. Take a look at the following thread and see if that helps :)

www.bobtait.com.au/forum/instrument-rati.../4784-exercise-11-q4

Cheers,

Rich
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  • linc90
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linc90 replied the topic: ADF question

Thanks Rich can you clarify heading after intercept ? In the question it said I would hold a heading of 155 ?
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Richard replied the topic: ADF question

Hi Linc,

There are two ways to confirm the new HDG after re-intercept.

1) Using the HAT trick.
H +/- A = T

We know we have 10 degrees of left drift so the value for A is -10 TO. The Track we need is 145 degrees so our HAT trick becomes:

HDG - 10 TO = 145

HDG must be 155 degrees.

2) Use the drift diagram from Navigation.

If we know we have 10 degrees of left drift and we need to track 145 degrees, the heading must be 10 degrees further to the right i.e. 155 degrees.

We have 10 degrees of left drift so if you want to maintain a track of 145 degrees you will need to hold a heading of 155

Cheers,

Rich
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Jimbob replied the topic: ADF question

Hi Richard,

Sorry to resurrect this, but I am also stumped.

It appears to me from my own diagram and the diagram on page 53 that the aircraft has drifted to the right of the FPT. We want to be tracking 145 degrees to the station, but we're actually right of that tracking 140 degrees to the station. After turning left onto a heading of 085 to re-intercept the 145 degree FPT, it doesn't make sense that we would then correct our original heading of 150 10 degrees to the right to maintain track. The whole reason we're right of track in the first place is because our original heading of 150 allowed us to drift to the right. To me it only seems logical that once we're back on the PFT we should correct our heading 5 degrees to the left to maintain track, i.e. heading 145.

I'd greatly appreciate any input, because I am verrrrry confused :)
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bobtait replied the topic: ADF question

Nobody ever said that the wind was the reason you were off track in the first place. All you know is that your are presently right of the required track of 145° to the station.

Think of it this way. You are presently tracking towards the the station on the 140 inbound track with a heading of 150°M. ATC require you to intercept the 145°M inbound track. You decide to make a 60° intercept of that track (any aircraft on the right of 145°M would use a heading of 085° to make a 60° intercept of the 145° inbound track).

It doesn't matter what you were doing before that, as long as you know you were right of the 145, the heading required for a 60° intercept is always going to be 085°M.

Once established on the 145° track, it is reasonable to assume that you will still have to allow for 10° of left drift.

Bob
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Jimbob replied the topic: ADF question

Thanks a lot for your response Bob! That clears it up for me.

I had been presuming the TE had been caused by wind and that we were trying to fix that by re-intercepting track and compensating heading once back on route, not that we were just adjusting our track (for whatever reason). It makes sense then that we'd adjust our drift angle instead once on the new route. As you say on page 31, understanding drift is a most vital concept.
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bobtait replied the topic: ADF question

Yes, you would think that drift would be a simple concept to grasp. But it does require some careful thought. In any case you couldn't work out a track error unless you knew the distance off track and distance from the last on-track fix. This question never was a 1 in 60 type question.

Bob
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