Aviation medicine · Patient guide · 6 min read
Fitness to fly assessment, hypoxic challenge test and structured medical review for travel with lung, heart or complex conditions.
A structured pre-flight medical assessment for patients with respiratory, cardiac, neurological or complex conditions. Includes a hypoxic challenge test (HCT), oxygen prescription and MEDIF form. Aligned with BTS aviation guidelines.
Key facts
What a fitness to fly assessment actually covers.
A structured medical review that produces the paperwork airlines require — with the hypoxic challenge test at its centre.
- 01
Definition
A structured medical assessment for airline travel with an underlying respiratory, cardiac, neurological or complex condition.
- 02
Hypoxic challenge test (HCT)
Simulates cabin altitude by breathing 15% oxygen for 20 minutes under continuous SpO₂ monitoring.
- 03
Who it’s recommended for
Patients with FEV1 < 50% predicted or resting SpO₂ < 95% — plus other BTS aviation criteria.
- 04
Oxygen prescription
Typical in-flight prescription is 2 L/min, titrated to keep SpO₂ ≥ 90% during the HCT.
- 05
MEDIF form
Completed medical information form provided for the airline to authorise travel and any in-flight oxygen.
- 06
Guidance
Aligned with British Thoracic Society (BTS) aviation guidelines and CAA UK medical guidance.
Preparation and steps
From referral to MEDIF — what happens, in order.
One clinician from first contact to the fit-to-fly letter — usually inside a working day.
- 01
Before
Referral or self-book
Send us a referral, or book directly — we handle airline paperwork and insurer pre-authorisation.
- 02
Before
Detailed history and medications review
A structured clinician-led history: condition, exacerbations, oxygen use, current medications and flight plan.
- 03
On the day
Baseline spirometry and SpO₂
Resting oxygen saturations, spirometry (FEV1, FVC) and clinical examination.
- 04
On the day
Hypoxic challenge test — 15% O₂ for 20 min
You breathe a 15% oxygen mixture (equivalent to 8,000 ft cabin altitude) via a well-fitted mask.
- 05
On the day
SpO₂ and symptoms monitored
Continuous pulse oximetry, ECG where indicated, and symptom review throughout the challenge.
- 06
After
Fit-note and MEDIF completed
A clear fit-to-fly letter and the airline MEDIF form are completed the same day.
- 07
After
Airline notification instructions
We tell you exactly what to send, to whom, and by when — including any oxygen supplier hand-off.
What it shows
What a fitness to fly assessment answers.
The specific measurements and outcomes that shape whether you fly, and how.
-
Baseline resting SpO₂
Your oxygen saturation at sea level — the starting reference for interpretation.
-
Hypoxic challenge SpO₂ nadir
The lowest saturation reached under simulated cabin altitude — the number that drives the decision.
-
Symptom response during HCT
Breathlessness, chest discomfort, dizziness or arrhythmia during the challenge.
-
Oxygen needed in flight
Whether supplemental oxygen is required, and at what flow rate.
-
Fit-to-fly clearance
A clear yes / conditional / no decision, in writing, that airlines accept.
-
MEDIF documentation
The airline’s medical information form completed and signed by the assessing clinician.
-
Cabin altitude equivalent
Interpretation against typical commercial cabin altitudes of 6,000–8,000 ft.
-
Red flag: unable to maintain SpO₂ > 85% on room air — do not fly / arrange oxygen and specialist review
Travel is deferred pending oxygen provision and specialist optimisation.
Next steps
Treatment and travel-preparation options.
What we can arrange alongside the assessment — the practical measures that get you safely on a plane.
-
In-flight oxygen prescription
Written prescription with flow rate and duration — sent to your airline’s medical team.
-
Nebuliser plan for asthma
Rescue plan, spacer technique check and airline-approved device paperwork.
-
CPAP / BiPAP for OSA in flight
Device compatibility, battery paperwork and airline pre-approval for use in the cabin.
-
Cardiology optimisation before travel
Onward cardiology review for arrhythmia, heart failure or ischaemic disease.
-
Anticoagulation for DVT risk
VTE risk stratification and prophylaxis plan for longer sectors.
-
Rescue medication supply
Named-patient supply, letters for controlled drugs and cabin-carriage guidance.
-
Structured medical clearance letter
A single, airline-ready letter that summarises fitness, oxygen and medications.
-
Repeat HCT for progressive disease
Interval reassessment for conditions that change — COPD, ILD, pulmonary hypertension.
Red flags
When flying should be deferred or reconsidered.
Situations where we would not clear you to fly without further work-up or specialist input — the safest use of your time.
-
Recent MI or stroke
Travel is typically deferred; timing depends on severity and revascularisation.
-
Uncontrolled arrhythmia
Rate/rhythm control and specialist review before clearance is issued.
-
Recent pneumothorax
Full radiological resolution is required prior to any flight clearance.
-
Severe COPD with hypercapnia
ABG review and specialist respiratory optimisation before assessment.
-
Severe pulmonary hypertension
Cabin hypoxia risk is significant — cardiology / PH-service input required.
-
Recent VTE without anticoagulation
Anticoagulation plan needed before travel is considered.
-
Advanced pregnancy (> 36 weeks)
Most airlines will not carry — check carrier policy and obstetric clearance.
-
Post-op < 2 weeks (thoracic / abdominal)
Surgical review and imaging as appropriate before flight is considered.
-
Uncontrolled seizure disorder
Neurology optimisation before any clearance is issued.
Frequently asked
Everything we get asked about fitness to fly.
Quick answers on the HCT, the MEDIF form, oxygen prescriptions and turnaround times.
-
What is a fitness to fly assessment?
A structured pre-flight medical assessment for patients with respiratory, cardiac, neurological or complex conditions. It confirms whether it is safe to fly, whether supplemental oxygen is needed, and produces the airline paperwork (MEDIF) required to travel.
-
What is a hypoxic challenge test?
The HCT simulates commercial cabin altitude by having you breathe a 15% oxygen mixture for around 20 minutes while your oxygen saturations, symptoms and ECG (where indicated) are monitored. The lowest saturation reached guides whether in-flight oxygen is needed.
-
Who should have a fitness to fly assessment?
BTS aviation guidance recommends assessment for patients with FEV1 below 50% predicted, resting SpO₂ below 95%, significant cardiac disease, prior in-flight symptoms, or those already on long-term oxygen therapy — among other criteria.
-
What is a MEDIF form?
The Medical Information Form is a standard airline document confirming your medical condition, fitness to travel and any in-flight requirements — typically oxygen, CPAP or medication. It is completed by the assessing clinician and submitted to the airline’s medical team.
-
How is oxygen prescribed for a flight?
The flow rate is titrated during the HCT to maintain SpO₂ at or above 90%. A typical prescription is 2 L/min via nasal cannula, but this is individualised. We supply a written prescription and coordinate with airline-approved oxygen providers.
-
How quickly can I be assessed?
We can usually arrange assessment within a few working days, and provide the fit-to-fly letter and MEDIF form the same day. Urgent slots are available for imminent travel.
Sources
The guidance behind this page.
Reviewed on 2026-07-30. Next scheduled review: 2027-07-30. Reviewed by Pulse Atlas Editorial Board, .
Related tests
Looking for a different test?
-
Cardiopulmonary exercise test (CPET)
Integrated cardiac and pulmonary exercise physiology — the gold standard for exercise intolerance.
Learn more -
At-home sleep study
Home polygraphy for suspected obstructive sleep apnoea and travel planning with CPAP.
Learn more -
Blood tests
Comprehensive blood panels — baseline health, medication monitoring and travel preparation.
Learn more -
All tests
Browse every test and procedure we arrange.
Learn more -
Asthma
Related condition guide.
Learn more -
COPD
Related condition guide.
Learn more -
Continuous Positive Airway Pressure
Related treatment option.
Learn more -
Complementary Alternative Medicine
Related treatment option.
Learn more
In practice, in London
The London pathway for fitness to fly assessment
With fitness to fly assessment, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. Waiting lists on the NHS for fitness to fly assessment vary widely by borough and by how the GP letter reads. Privately in London, we can normally offer a slot inside the same week, sometimes within 48 hours if there’s a cancellation. The difference isn’t clinical quality — the consultants are frequently the same faces you’d see on the NHS — it’s the calendar.
A private fitness to fly assessment pathway in London usually looks like this: an initial consultation, any diagnostics booked at a nearby facility (most within Zone 1 or 2), and a written report sent to you and your GP within a few days. The consultants we work with hold NHS posts alongside their private lists, which keeps the standards consistent across both settings. For fitness to fly assessment specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
There are a lot of consultants in London who can technically handle fitness to fly assessment. Fewer who do it week in, week out for the exact question you’re bringing. We spend most of our time working out which is which — and being straight when a different test or a different specialist would serve you better. Everything runs to CQC, GMC and Royal College standards; the choice is about fit, not floor.