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## RMI

• Posts: 130

### MissSoph created the topic: RMI

I’m having a bit of a hard time breaking down this question…l
Maintain a heading of 070 since passing over the Ndb
Tail of RMI needle indicates 055…constant
FPT is 080 and you decide on a 30 degree intercept of the FPT…
Find the heading to use for the intercept, the indication of the tail of the RMI needle when the FPT is intercepted the heading to fly to maintain the FPT and drift experienced….

I’m a bit confused about the 30 degrees… is that now my track error instead of working it out like I would normally?
If I use the H - or - A = T I though the T was the TMG, but how come in this question they say it’s the heading to maintain for the FPT?

I’m sure I’m missing something in the readings about RMI… I’ll go back over it again… and read it Slooooooowlyyyyyy )

• John.Heddles
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### John.Heddles replied the topic: RMI

RMI 055 makes little sense. Can you check if it should be 255, please?

30 degrees is just the (very typical) angle you are choosing to cross the outbound track as part of your intercept strategy. In practice, you will lead a bit before you get to that angle so you don't fly through the desired track.

Q1. Which side of track are you?

Q2. Which way do you need to turn to acquire the desired track?

Q3. If you were not to allow for lead, what angle would you cross the outbound track. In which case what would the ADF (or RMI, in this case), indicate?

Q4. From the initial data, what is your drift?

Q5. Assuming that that drift will still apply, what drift allowance will you need to maintain the desired track once you have intercepted.

RMI is just a super easy to use ADF - think ADF with a DG overlaid.

Engineering specialist in aircraft performance and weight control.

• Posts: 130

### MissSoph replied the topic: RMI

Thanks John… I have included a pic of the question that might help make more sense for you… as you can see…
I’m not having any luck making sense of it… well… I think I kinda worked it out … I might put that working out in as well….

• Posts: 130

### MissSoph replied the topic: RMI

The pic of the question
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• John.Heddles
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• Posts: 665

### John.Heddles replied the topic: RMI

Thanks, Sophie, I misunderstood the story before - mea culpa. With the additional information it is abundantly clear. I'll come back, probably this evening and complete the story for you.

Generally, it's better to cut and paste the question so that the reader gets all the story rather than having the risk of misinterpreting anything.

Probably, where you are getting yourself confused, is attacking the question via canned formulae rather than orientation - or, perhaps, I'm just the old codger I am, having been brought up on ADFs before being let loose on big aircraft with RMIs ?

Engineering specialist in aircraft performance and weight control.

• John.Heddles
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### John.Heddles replied the topic: RMI

I haven't forgotten this one, Sophie. Been a tad busy elsewhere.

Will try to finalise a response tonight.

Engineering specialist in aircraft performance and weight control.

• Posts: 105

### Bosi72 replied the topic: RMI

Let me try help..
1. lets find what's wind doing to us, i.e. lets find the drift.

drift is 15L
blue colour is what we need to calculate.

2. then to intercept 80deg radial by 30deg, we need to fly 80+30 = 110deg

3. finally if we set heading to 080, the wind will push us again to the left. however we already know the wind is drifting aircraft by 15deg, so lets calculate new corrected heading by adding drift to the track.

again blue colour is what we need to calculate.

Hope above make sense, if not have a look at page 51 CPL Navigation book, topic Factors that affect drift and try understanding diagrams.

Diagrams are very helpful. Put track in a rectangle and on top in the middle. Heading is round same as DG in aircraft and it can be left or right. Headings greater than track will go to the right (clockwise), headings less than a track will go to the left (counter clockwise).
Draw the aircraft with nose pointing to the heading. If left wing is pointing to the track, then it will be left drift, and vice versa with right wing=right drift.
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• John.Heddles
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### John.Heddles replied the topic: RMI

Ah, Bosi has saved me the trouble - well done.

The only practical comment to emphasise, is that, as part of the intercept of the final, desired track, you

(a) apply a suitable amount of lead to commence the turn (so you don't fly through the outbound track), and then

(b) roll out onto the expected heading, and then, for a little while

(c) check that the expected heading actually provides the correct navigation solution and you end up tracking the desired outbound track.

Engineering specialist in aircraft performance and weight control.