The CAA Class 3 Medical for Air Traffic Controllers: What Is Actually Tested

Every licensed UK air traffic controller holds a CAA Class 3 medical certificate. It is the requirement candidates worry about most and understand least, largely because the CAA publishes the detail across several pages written for aeromedical examiners rather than for applicants.

This guide pulls the published standards together. Where the CAA states a figure, it is quoted here. Where it does not, that is said rather than filled in with a number from a forum.

Where the medical fits, and who does it

The initial examination must be carried out by an aeromedical examiner (AME) at an aeromedical centre (AeMC) — not your GP, and not any AME working alone. The CAA warns that an examination at an AeMC may take up to four hours, which surprises people who have booked half a morning off.

There is no minimum age to apply for a Class 3 certificate, though applicants under 17 may need additional specialist paediatric review.

You will be asked in detail about your medical history. The CAA's advice is to bring reports from your GP or treating specialist for any major illness or medical event. Minor things — appendicitis, a broken arm — are not major events but should still be declared.

What the initial examination includes

The CAA lists the initial examination as:

How long it lasts

Individual tests are then repeated on their own cycles rather than at every examination. The ECG is done at initial, then every 48 months under 30 and at every examination from 30 onwards. The audiogram is done at initial, then every 48 months under 40 and every 24 months from 40. Tonometry is done at initial and at the first examination, then over 40. Blood lipids are checked at initial and again at 40.

Hearing: the published limits

This is one of the few places the CAA publishes hard numbers, and they apply at both initial and renewal. The maximum acceptable hearing loss on an audiogram is:

Eyesight

Corrected vision is acceptable — wearing glasses or contact lenses does not stop you becoming a controller. What your prescription changes is the re-examination cycle. A comprehensive ophthalmological examination is required at initial, then:

The CAA publishes the detailed initial visual standards separately, on its air traffic controller visual standards page. If your prescription is near the edge of anything, that page and a conversation with an AeMC are worth more than any guide, including this one.

Colour vision — the part worth reading carefully

Colour vision is where the ATCO standard is genuinely unusual, and where the rules changed recently.

The regulation requires ATCO applicants to be normal trichromats. The CAA states in its own policy document that this "is much stricter than that for pilots" — which is the opposite of what most people assume.

UK aeromedical centres measure this with the CAD test (Colour Assessment and Diagnosis), not simply with Ishihara plates. The published thresholds are:

That third row is new and matters. Under a policy the CAA updated in April 2026, an applicant with a mild deutan deficiency in that band can be granted a Class 3 certificate endorsed "SSL Special restriction(s) as specified: issued by licensing authority in accordance with Part ATCO.MED.B.001", provided the rest of the application is satisfactory.

It is not automatic. The applicant must provide an assessment report signed by a trainer when their student ATCO licence is issued, confirming no issues identifying colours during initial training, and a further report on completion of unit training.

The CAA is candid about why: people in this band have difficulty with small red-green signals near threshold, but perform normally with the suprathreshold colours used in a modern ATC environment, where display adjustments are also possible. The CAA says it intends to change the implementing rule from "normal trichromat" to "colour safe" in a current rule-making task, and that this policy is an interim solution until then.

It is also rare — the CAA puts it at one to two applicants a year.

What to do with this before you apply

If you are still at the aptitude stage, the medical comes later — but it is worth knowing where the hard limits are before you invest months in preparation. Our guide to the full UK requirements covers age, nationality, security clearance and qualifications, and the NATS Stage 1 aptitude guide covers the test that comes first.

*Standards change, and this page reflects the CAA's published guidance as read in September 2026. The CAA's own pages are the authority — always confirm with an aeromedical centre before making a decision about your application.*