The most important preflight inspection is the one no checklist card prints: the walk-around you do on yourself. A medical certificate proves you were fit on the day an examiner saw you; whether you are fit for this afternoon's flight, after this week's sleep, last night's dinner party and this morning's headache tablet, is a judgement the rules place squarely on you. This guide covers the self-assessment habit, the alcohol rules with actual numbers, and the medication and diving traps that catch conscientious pilots.
This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.
The rules behind the self-check
The legal anchor is broader than most pilots remember. The FAA's 14 CFR 61.53 prohibits acting as a required crewmember while you know of any medical condition, or are taking any medication, that would make you unable to meet the standard of your medical certificate. EASA's air operations rules, in the Easy Access Rules for Air Operations, likewise require that crew do not perform duties when unfit, whether from injury, sickness, medication, fatigue or the influence of psychoactive substances. Neither authority waits for a doctor to ground you: the moment you are not fit, the certificate in your pocket stops being permission.
IMSAFE: six questions, honestly answered
The standard tool for that judgement is the IMSAFE checklist, described in the FAA's Pilot's Handbook of Aeronautical Knowledge:
- Illness. Any symptom counts, and altitude amplifies some of them: a blocked sinus or middle ear that is a nuisance at sea level can become disabling pain in a climb or descent, per the guidance in AIM 8-1-1.
- Medication. What have you taken in the last day or two, prescribed or off the shelf, and what does it do to alertness and judgement?
- Stress. A dispute at work, money trouble, a family illness: pressure parked in the back of the mind takes capacity from the front of it, and the flight deck is a bad place to discover how much.
- Alcohol. Hours since the last drink, and quantity, against the rules below, remembering that the legal floor is not the safe ceiling.
- Fatigue. Sleep actually obtained, not caffeine consumed since. Fatigue is insidious precisely because it erodes the judgement you would use to detect it; the structural defences are the rest requirements and duty limits, but the day-of-flight call is yours.
- Emotion. Is your head in this flight? Anger, grief and euphoria all fly badly.
One honest no is a no-go. Treat yourself the way you would treat the aircraft: unserviceable is unserviceable, whoever is disappointed.
Alcohol: the numbers and the myths
The FAA's rule, 14 CFR 91.17, sets three separate tests, and you must pass all of them: no acting or attempting to act as a crewmember within 8 hours of consuming alcohol, none while under the influence, and none with a blood alcohol concentration of 0.04 per cent or more. The famous "8 hours bottle to throttle" is therefore a floor, not a clearance: after a heavy evening you can be past 8 hours and still fail the other two tests. The FAA's own guidance in AIM 8-1-1 recommends allowing at least 12 to 24 hours between drinking and flying, depending on quantity, and notes that a hangover is itself impairing even once the alcohol has gone.
EASA reaches the same place by a different route, and it is worth knowing that it has numbers of its own rather than only a general prohibition. The hard rule, CAT.GEN.MPA.100(c) in the air operations regulation, forbids a crew member from performing duties on an aircraft under the influence of psychoactive substances or when otherwise unfit. The figures sit in the acceptable means of compliance to it, which requires the operator's own instructions to be no less restrictive than: no alcohol within 8 hours of the specified reporting time for a flight duty period or the start of standby; a blood alcohol level at the start of the FDP no higher than the lower of the national limit or 0.2 grams per litre; and no alcohol at all during the flight duty period or while on standby. So the European 8-hour figure matches the FAA's, and the concentration limit is five times lower than the FAA's 0.04 per cent.
The UK writes a sharper number still into criminal law, though it turns out to be the same number as EASA's. The Railways and Transport Safety Act 2003 sets a prescribed limit for aviation of 20 milligrammes of alcohol per 100 millilitres of blood for flight crew, cabin crew and controllers, and separately makes it an offence to perform an aviation function while impaired. Twenty milligrammes per 100 millilitres is 0.2 grams per litre: EASA's ceiling and the UK's criminal limit are the same concentration written two ways, and both are a quarter of the 80 milligramme drink-driving limit in England and Wales. At a quarter of the driving limit, the practical planning assumption is close to zero: alcohol from the night before can still be aboard at report time. Across the EU, Regulation (EU) 2018/1042 added random alcohol testing of flight and cabin crew during ramp inspections, tested against that same 0.2 figure or the national limit if it is lower, so the question is no longer hypothetical even for a crew that feels fine.
The myths need retiring too: coffee, cold showers and fresh air do not clear alcohol. Only time does, at the liver's own unhurried rate, and nothing you drink, eat or breathe changes it. Many operators set stricter company limits than any of the above, and those bind you as well.
Medication: the double trap
Medication grounds pilots twice over. The first trap is the drug itself: sedating antihistamines in allergy and cold remedies, sleep aids, strong painkillers and anti-anxiety medication all degrade the alertness and judgement flying spends. The second trap is quieter: the condition you are treating. If you need the tablet, ask what the symptom says about your fitness before asking whether the tablet is allowed.
The FAA's 91.17 also prohibits acting as a crewmember while using any drug that affects faculties in any way contrary to safety, and 61.53 catches the underlying condition. The practical habits: read the label for drowsiness warnings, be suspicious of anything new, and ask an aviation medical examiner, rather than the pharmacy counter, whether a medication is compatible with flying, because plenty of everyday remedies are not. Authorities publish differing guidance on specific drugs, which is one more reason the AME is the right desk to ask.
Scuba, blood and the body's slow clocks
Some fitness items have explicit wait times. After scuba diving, excess nitrogen stays dissolved in the tissues for hours, and climbing to altitudes that are normally benign can bring it out of solution as decompression sickness. The FAA's guidance in AIM 8-1-2 recommends waiting at least 12 hours after diving that did not require controlled decompression before flying up to 8000 ft, and at least 24 hours after decompression-stop diving or before any flight above 8000 ft.
Read that 8000 ft carefully, because it is not the figure most pilots assume. The AIM states that these are actual flight altitudes above mean sea level, not pressurised cabin altitudes, and it says why: the recommendation has to allow for the aircraft depressurising in flight. A pressurised jet cruising at FL350 with a 6000 ft cabin is still, for this purpose, "above 8000 ft", so the 24-hour figure applies. Reading it as a cabin altitude quietly halves the wait on exactly the flights where a decompression would be most punishing. The same chapter is worth reading on hypoxia and hyperventilation, which pair with the supplemental oxygen rules covered elsewhere in this library.
A worked example
You are due to fly at 0900. Running IMSAFE the evening before: no illness; you took a night-time cold remedy two nights ago but nothing since and the symptoms are gone; work is calm; you expect a full night's sleep; and you are looking forward to the flight. Then the alcohol letter. You had two glasses of wine, finishing at 2130.
Do the arithmetic rather than the vibe. From 2130 to an 0900 report is eleven and a half hours. The FAA's 8-hour floor in 91.17 is comfortably met, and after two glasses at that distance you are most unlikely to be near 0.04 per cent, or near the 0.2 grams per litre that EASA and UK law both set. So the rule says yes.
But the guidance does not. Eleven and a half hours is short of the AIM's recommended 12 to 24 hours, by half an hour. Not "comfortably inside it": below it. That gap between what is legal and what is recommended is the entire point of the letter, and the honest reading is that the flight as planned does not meet the standard the FAA itself suggests, even though nothing about it is unlawful.
Which makes the fix small and obvious. Finish the same two glasses at 2030 instead, and the report is twelve and a half hours later, inside the recommended window. The change is to the evening, not to the flight. And had it been six glasses finishing at midnight, no arithmetic would have rescued it: nine hours, clear of the 8-hour floor, and nowhere near fit.
Common pitfalls
- Treating 8 hours as an all-clear. It is one of three FAA tests, and the FAA's own guidance recommends 12 to 24 hours depending on quantity. Clearing the rule and clearing the guidance are different arithmetic, and eleven and a half hours clears only the first.
- Forgetting how low the European limits are. Twenty milligrammes per 100 millilitres, which is EASA's 0.2 grams per litre, is a quarter of the UK driving limit and a fifth of the FAA's 0.04 per cent; plan as if it were zero.
- Trusting over-the-counter remedies. Sedating antihistamines are the classic quiet grounding; ask an AME, not the label alone.
- Medicating the symptom and ignoring its message. The condition can be more disqualifying than the drug.
- Flying too soon after diving, or reading 8000 ft as a cabin altitude. It is an actual flight altitude AMSL, so a pressurised flight in the flight levels needs the 24-hour wait however comfortable the cabin.
- Letting schedule pressure mark your own IMSAFE. The checklist only works when a no is allowed to mean no.
In Pilot EFB
Pilot EFB cannot tell you whether you are fit to fly, and it never will: fitness is a judgement between you, the rules and, where needed, your medical examiner. What the app does is keep the supporting record-keeping tidy: a personal tracker for your medical and rating expiry dates with reminders as they approach, your duty and rest picture against the flight time limits you plan under, and personal minimums you define yourself, flagged against decoded weather without ever recommending a go. All of it is decision support for your own planning, verified against official sources. Pilot EFB is not a certified Electronic Flight Bag, so treat it as a study and planning aid, and treat the person in the mirror as the final airworthiness inspector.