Avielevate / DGCA CPL papers / Air Navigation / Convergency
Convergency — DGCA CPL Air Navigation
Chapter GN04 of the Air Navigation paper. 32 practice questions in the Avielevate bank, every one with its answer key, filterable into a timed set on this chapter alone.
What this chapter covers
The learning objectives we file Convergency questions under, and how many sit behind each. These come straight out of the bank and are regenerated whenever it changes — they are what is there today, not a claim.
| Learning objective | In the bank |
|---|
| __GEN__ General | 32 questions |
Sample Convergency questions, answered and explained
Real questions from this chapter, with the answer marked and the reasoning written out — the same explanations you get inside the app.
0212063 · Convergency
Place A is at 70°00′S 060°00′W and place B is at 70°00′S 030°00′E. Determine the initial great circle track from A to B.
- A270°
- B132°
- C312°
Why that is the answer
A **great circle** (GC) is the shortest route between two places on the globe. The meridians (lines of longitude) lean towards each other as they run to the poles, so a great circle cuts each meridian at a slightly different angle and its true track keeps changing along the way. A **rhumb line** (RL) cuts every meridian at the same angle, so its track never changes, but it is a little longer.
The total change of GC track between the two places is the **convergence** = change of longitude × sin(mean latitude). The rhumb-line track lies exactly halfway between the GC tracks at the two ends, so the angle between the GC and the RL at either end, the **conversion angle** (CA), is half the convergence.
Which way does the GC track change? In the Northern Hemisphere it **increases** when flying east and **decreases** when flying west. In the Southern Hemisphere it is the other way round. This is because the great circle always bows towards the nearer pole, so it lies on the pole side of the rhumb line.
When both places are on the same parallel, the rhumb line runs along the parallel (090° or 270°), and the great circle starts the CA away from it, on the pole side.
**Apply it**
Change of longitude: 060°W to 030°E = 60° + 30° = 90°, flying east, so the RL is 090°.
Convergence: 90 × sin 70° = 90 × 0.940 = 84.6°.
CA: 84.6 ÷ 2 = 42.3°.
Southern Hemisphere, so the GC lies on the south side. Facing east, south is on your right, which means a larger number.
Initial GC track: 090° + 42.3° = 132.3°.
So the initial great-circle track is about **132°**. The route dips far towards the South Pole, which is why it starts heading south-east even though B is due east of A.
**Tip:** the rhumb line is the average of the two great-circle tracks, and the great circle always lies on the pole side of it.
0212064 · Convergency
On a Mercator chart, the great-circle track from A (25°00'S 010°00'W) to B (35°00'S 040°00'W) is 242° measured at A. What is the rhumb-line track from B to A?
- A249.5°
- B075°
- C069.5°
Why that is the answer
A **great circle** (GC) is the shortest route between two places on the globe. The meridians (lines of longitude) lean towards each other as they run to the poles, so a great circle cuts each meridian at a slightly different angle and its true track keeps changing along the way. A **rhumb line** (RL) cuts every meridian at the same angle, so its track never changes, but it is a little longer.
The total change of GC track between the two places is the **convergence** = change of longitude × sin(mean latitude). The rhumb-line track lies exactly halfway between the GC tracks at the two ends, so the angle between the GC and the RL at either end, the **conversion angle** (CA), is half the convergence.
Which way does the GC track change? In the Northern Hemisphere it **increases** when flying east and **decreases** when flying west. In the Southern Hemisphere it is the other way round. This is because the great circle always bows towards the nearer pole, so it lies on the pole side of the rhumb line.
On a **Mercator chart** a rhumb line is drawn as a straight line, while a great circle appears as a curve bowing towards the pole.
**Apply it**
Change of longitude: 010°W to 040°W = 30°, flying west.
Mean latitude: (25 + 35) ÷ 2 = 30°S.
Convergence: 30 × sin 30° = 30 × 0.5 = 15°, so the CA is 7.5°.
Southern Hemisphere, so the GC lies on the south side. Facing 242° (west-south-west), south is on your left, which means a smaller number. So the GC (242°) is the smaller one and the RL is larger: 242° + 7.5° = 249.5° from A to B.
A rhumb line has the same track all the way, so from B to A it is simply reversed: 249.5° − 180° = 069.5°.
So the rhumb-line track from B to A is **069.5°**.
**Tip:** the rhumb line is the average of the two great-circle tracks, and the great circle always lies on the pole side of it.
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Frequently asked
How many Convergency questions are there for the DGCA CPL Air Navigation paper?
Avielevate's bank carries 32 published Convergency questions for Air Navigation, mapped across 1 learning objective. Every one has its answer key, and explanations are being written across the whole bank.
How much of the Air Navigation paper is Convergency?
The DGCA does not publish a per-chapter breakdown of its papers, so nobody can honestly tell you — and we will not guess. What we can tell you is what students who have just sat a paper reported meeting, which is measured rather than rumoured: that is the exam recall report inside the app.
What is the best way to revise Convergency?
Sit a short timed set on this chapter alone, tag how sure you were of each answer, then drill the two that actually leak marks: the ones you got right while guessing, and the ones you got wrong while confident. Avielevate does that tagging for you and puts anything you got wrong back in front of you on a spaced schedule.
The rest of the Air Navigation paper
One account covers every chapter of every paper.
← All Air Navigation chapters · All six DGCA CPL papers