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Bearings

Old 11th Nov 2015, 06:59
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Bearings

Hi Guys, I seriously have a problem with the NDB bearings and getting the problem solved, as i'm passing my written cpl exam this week, i'm a bit nervous about this topic , if some one of you may help me out with this, i would be really thankful.
I got two questions, got them from a book but i couldn't understand from where did they get the correct answer, here are the questions,

1-An aircraft is on a heading of 120° and the fixed ADF indicator indicates 340°. There is no wind blowing. In order to intercept a magnetic track of 210° outbound from the selected beacon at 30°, the aircraft must be flown on a heading of:
a-240°
b-180° *
c-360°
d-060°
the correct answer is B: 180°

2-The VOR indicator in an aircraft is centred when 200 is selected on the OBS. The TO/FROM flag indicates TO. In order to intercept radial 100 inbound at 90°, the aircraft mush be turned onto a heading of!
a-010°
b-190° *
c-020°
d-110°
the correct answer is B: 190°

I would love to get an explanation for this topic, Thankkkss

Last edited by lukyduky81; 11th Nov 2015 at 16:04.
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Old 11th Nov 2015, 16:12
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Get a sheet of paper and protractor and draw the situations out. It shoukd all make sense then.

G
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Old 12th Nov 2015, 16:55
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Thx

I tried to figure out, drawing the situation, unfortunately my brain was locked for these questions. I did receive a real clear answer from Keith Williams, weird i didn't find his/her answer in the forum, so i'll share and paste the email right here. Thank you Keith, everything is clear now
As Genghis has said, the best way is to sketch the situation and it should all become clear.

But the head banging figures in your post suggest that you might be having difficulty is deciding how and where to begin. Let’s try to do it by visualizing the situation.


---Quote---
1-An aircraft is on a heading of 120° and the fixed ADF indicator indicates 340°. There is no wind blowing. In order to intercept a magnetic track of 210° outbound from the selected beacon at 30°, the aircraft must be flown on a heading of:
a-240°
b-180° *
c-360°
d-060°
the correct answer is B: 180°
---End Quote---

To simplify things let’s imagining that the aircraft heading is due north (360 degrees).

The fixed ADF indicator shows 340, which means that the beacon is at 340 degrees relative to the aircraft. 340 degrees is 20 degrees to the left of our heading of 360, so the beacon is 20 degrees to the left of the nose of our aircraft.

But the aircraft heading is 120, so the beacon, which is 20 degrees left of our nose, must be at 120 – 20 = 100 degrees. This means that the beacon is at a position on a bearing of 100 degrees from the aircraft.

We can now forget our 120 degree heading because it does not affect the rest of the question.

The beacon is at 100 degrees from the aircraft, so it is out to the East and slightly south of us. If we sketched it to scale with North at the top of the sheet, we would have something like the beacon about 7.5 cm to the right and 1 cm below the aircraft.

We want to intercept the 310 radial from the beacon, but again let’s begin by simplifying the situation.

If we were to fly due south (180 degrees) we would be flying parallel to the 180 degree radial from the beacon.

The difference between 210 degrees and 180 degrees is 30 degrees, so the 210 radial crosses the 180 radial at an angle of 30 degrees running west and south. So it passes to the south of us. And because the 180 radial and the 210 radial cross at 30 degrees, if we fly south at 180 degrees we will also cross the 210 radial at 30 degrees.

So to intercept the 210 radial at 30 degrees we must follow a track of 180 degrees.

---Quote---
2-The VOR indicator in an aircraft is centred when 200 is selected on the OBS. The TO/FROM flag indicates TO. In order to intercept radial 100 inbound at 90°, the aircraft mush be turned onto a heading of!
a-010°
b-190° *
c-020°
d-110°
---End Quote---
The needle is centred when we have 200 degrees selected on the OBS and “TO” indicated, so if we follow a track of 200 degrees we will cross the beacon. But the 200 degree radial point away from the beacon at an angle of 200 degrees, so we must be on the opposite side of the beacon. This means that our bearing from the beacon is 20 degrees. (200 - 180 = 20). So we are to the East and north of the beacon.

The 100 degree radial points away from the beacon at an angle of 100 degrees. This means that it is located to the East and south of the beacon, so it must pass directly south of the aircraft.

If we fly due south (180 degrees) we will cross the 100 degree radial. But the angle between our 180 degree track and the 100 degree radial will be (180 – 100 = 80) degrees. We want to intercept it at 90 degrees, so we need to increase our track angle by 10 degrees to intercept the radial at the required 90 degrees. This gives us our required track of 190 degrees.


You should now be able to sketch the situation. If you place the beacon at the centre of the page with north upwards we should have the aircraft in the north east quadrant and the 100 radial in the south east quadrant. If you use a protractor to draw the angle accurately you should the be able to draw the 190 track and find that it crosses the 100 degree radial at the required 90 degrees.
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