The ATC knowledge test: what to revise
For the current campaign, NATS includes an ATC knowledge test at the virtual assessment centre (stage 3), with a second part at the final stage. No aviation background is required to apply, so the test checks whether you've done your homework about the job, not whether you're already a controller.
By Carl Grzegorzek, an international air traffic controller with more than 20 years' experience training and assessing controllers. Updated 25 October 2026.
What to revise
| Topic | The essentials | In Holding Point |
|---|---|---|
| Radio language | Phonetic alphabet, numbers, standard words such as "affirm", "roger" and "wilco" | Chapters 2 and 13 |
| How aircraft fly | Lift, drag, stalls, take-off and landing performance, Mach number | Chapter 3 |
| Altimetry and weather | QNH, QFE and standard pressure, flight levels, transition altitude, METARs, low visibility | Chapter 4 |
| The three roles | Aerodrome, approach and area control, and how traffic passes between them | Chapters 5 and 6 |
| Airspace and navigation | Airspace classes, airways, SIDs and STARs, VORs, GNSS, ILS | Chapters 7 and 8 |
| Surveillance | Primary and secondary radar, transponders, squawk codes, ADS-B | Chapter 9 |
| Separation and wake turbulence | Why separation minima exist, vertical and radar separation, wake categories | Chapters 11 and 12 |
| Emergencies | Mayday and pan-pan, emergency squawks, how controllers help | Chapter 14 |
Test yourself
Answer each one out loud before opening it. If you can explain it simply, you understand it well enough for the test and the interview.
What are the three emergency squawk codes?
7700 for a general emergency, 7600 for radio failure and 7500 for unlawful interference (hijacking).
What is the difference between an altitude and a flight level?
An altitude is height above mean sea level, measured with the local pressure setting (QNH). A flight level is a pressure altitude in hundreds of feet, measured with the standard setting of 1013.25 hPa, so FL350 is 35,000 ft on the standard setting.
Why do controllers use flight levels above the transition altitude?
Every aircraft uses the same pressure setting, so vertical separation between them is guaranteed even when the local pressure changes.
What are the three main types of air traffic control?
Aerodrome (tower) control for the runway and the airport's immediate surroundings, approach control for arrivals and departures, and area control for aircraft en route.
What is wake turbulence, and when is it worst?
Rotating air shed from an aircraft's wingtips. It's strongest behind heavy aircraft flying slowly and in a clean configuration, such as on take-off and approach, which is why lighter aircraft are spaced further behind heavier ones.
How do you say 'Juliett' and the number 9 on the radio?
Juliett has two Ts in the ICAO alphabet, and 9 is spoken "niner" to avoid confusion with the German "nein".
What does 'cleared for take-off' mean?
The pilot may start the take-off. Controllers use the word "take-off" only when giving or cancelling this clearance, to prevent any misunderstanding.
What does an ILS provide?
An instrument landing system gives a precise lateral (localiser) and vertical (glide path) guide to the runway, so aircraft can land in poor visibility.
How to revise
- Revise little and often, alongside the aptitude practice, rather than in one block.
- Explain each topic aloud to someone else. The interview may ask technical questions too.
- Learn the phonetic alphabet and number pronunciation until they're automatic.
- Read about the training as well as the job: its length, the constant assessment, and what happens if you don't succeed.
Everything you need, in one bookHolding Point explains air traffic control from first principles: 20 chapters, more than 70 diagrams and quick-reference cards for revision.
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