Can you fly with…? Medical conditions A–Z
Straight answers on flying with a medical condition — what the CAA says, what airlines require, and when you need a certificate. Clinically reviewed.
The short answer. Most medical conditions do not stop you flying. What matters is whether the condition is stable, how recent any event was, and whether trapped gas or reduced oxygen affects it. Very few things are absolute barriers — an untreated collapsed lung is one of them.
Aircraft cabins are pressurised, but not to sea level. At cruising altitude the cabin sits at roughly the equivalent of 6,000 to 8,000 feet. Two things follow from that, and between them they explain almost every medical restriction airlines impose.
First, there is less oxygen available. A healthy passenger’s blood oxygen saturation typically drops a few percent — unnoticeable if your heart and lungs are working normally, much less so if they are not. Second, trapped gas expands by around a third. Any pocket of air sealed inside the body — in the middle ear, the sinuses, the bowel, the chest, under a plaster cast — gets bigger as the aircraft climbs, and shrinks again on descent.
Almost every restriction airlines and the CAA impose traces back to one of those two facts. Once you know which one applies to your condition, the advice usually makes sense rather than seeming arbitrary.
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Infections and illness
Ears, sinuses and balance
Heart and circulation
Lungs and breathing
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Long-term conditions
All conditions A–Z
The CAA’s practical test
If a passenger can walk 50 yards or metres at a normal pace, or climb one flight of stairs without significant breathlessness, supplemental oxygen should not usually be required.
It is a rough screen rather than a full assessment, but it is a good place to start — and if you cannot manage it comfortably right now, that is a reason to speak to a doctor before booking rather than after.
When you need more than a letter
For most conditions, a GP letter is what an airline wants, if anything. Formal medical clearance through a MEDIF form — reviewed by the airline’s own medical department — is usually needed for in-flight oxygen, stretcher travel, complicated pregnancy, recent serious cardiac or neurological events, and travel soon after major surgery. It takes days, so start early. How MEDIF clearance works.
Common questions
What medical conditions stop you flying?
Very few conditions are absolute barriers. The CAA lists an untreated pneumothorax, unstable angina, decompensated heart failure, uncontrolled arrhythmia, an uncomplicated heart attack within 7 days and a complicated one within 4 to 6 weeks. Most other conditions are about timing and stability, not diagnosis.
Do I have to tell the airline about a medical condition?
Not for a stable, long-standing condition. You do need to tell them if you need oxygen, a stretcher, significant assistance, or if you have had a recent serious medical event — in which case they will usually want MEDIF clearance from their own medical department.
Why does flying affect medical conditions at all?
Two reasons. Cabin altitude means less available oxygen, which matters if your heart or lungs have limited reserve. And trapped gas expands by about a third, which matters wherever air is sealed inside the body — the middle ear, sinuses, bowel, chest, or under a plaster cast.
Is there a general rule for whether I am fit to fly?
The CAA offers a useful practical test: if you can walk 50 metres at a normal pace or climb one flight of stairs without significant breathlessness, you are unlikely to need supplemental oxygen. It is not a complete assessment, but it is a sensible starting point.
Related
Sources. The airline and clinical facts on this page were checked against these primary sources on 24 August 2026. Airline policies change without notice — always confirm with your airline before you book or travel.
Need a fit to fly certificate?
If your airline or insurer has asked for medical confirmation, a GMC-registered UK GP can review your case and issue the letter the same day on weekdays.
Get startedReviewed by a GMC-registered GP. Full refund if a certificate cannot be issued on clinical grounds.