This subject looks like two unrelated piles of memorisation — cloud physics on one side, regulation numbers on the other. It is really two stories meeting at a point. The weather story: air rises, cools, and at some temperature can no longer hold its moisture, and almost every hazard follows from where and how fast that happens. The rules story: the pilot in command decides, and the regulations set a floor beneath that decision. Read the numbers as consequences rather than facts — the 1,000-foot floor over a town and the 500-foot floor elsewhere are one idea at two densities.
⚠️ Orientation for study, not flight instruction. Figures here were read from the electronic Code of Federal Regulations (eCFR) as it stood on 2026-08-01; verify any number against the current regulation.
Each chapter opens with the short version. Tap one to read the detail.
One mechanism, and the numbers that fall out of it
~2 min
Air cools as it rises, and cold air holds less moisture than warm air. Nearly all aviation weather is that single sentence playing out over different terrain, at different speeds. The standard atmosphere is the agreed reference everything else is measured against.
What actually hurts people, ranked by how quietly it arrives
~2 min
The hazards that kill are rarely the ones that look dramatic from the ground. Fog, ice and low-level wind shear all arrive without announcing themselves, and each has a specific formation condition you can check in advance.
Thunderstorms, and why the middle is the dangerous part
~2 min
A thunderstorm runs through three stages, and the violent one is the middle. The distinguishing feature is not the lightning — it is that updrafts and downdrafts exist side by side, which is what produces microbursts and the shear that comes with them.
Reading the reports as observation, forecast, or warning
~2 min
Weather products sort into three jobs: what is happening now, what is expected, and what is dangerous enough to interrupt you. Knowing which job a product does tells you how much to trust it and how quickly it goes stale.
The altimeter is a barometer, and it will lie to you predictably
~2 min
An altimeter measures pressure and displays altitude, so anything that changes pressure other than your height introduces error. The two that matter are flying into lower pressure and flying into colder air, and both err in the dangerous direction.
Deciding before the weather decides for you
~2 min
The go/no-go question is almost never a single dramatic call. It is a chain of small ones, each individually reasonable, and the useful skill is setting the trigger points while you are still on the ground.
Basic visual flight rules minimums, and why the table has that shape
~2 min
The cloud-clearance table looks arbitrary until you notice what it is protecting against: being surprised by an aircraft you cannot see. Every row is a judgement about how fast something might emerge from that cloud.
Certification, currency, and the compensation line
~2 min
Part 61 answers three separate questions people routinely merge: what your certificate lets you do, whether you are current enough to do it today, and whether money may change hands. Each has its own clock.
The operating rules, and the authority they are built around
~2 min
Part 91 reads as a list of numbers, but it is organised around one principle stated in its third section: the pilot in command is the final authority. Most of the rest sets minimums beneath that authority, and a few sections grant it back explicitly.
Where airspace class stops being geography and becomes a checklist
~2 min
Each airspace class bundles three separate requirements — equipment, clearance, and weather minimums — and they are not the same bundle. Most airspace errors come from carrying one class's bundle into another.
Documents, discrepancies, and what happens after
~2 min
Airworthiness is a continuing condition rather than a certificate in a folder, and the rules split it in two: what must be aboard, and who is responsible for the aircraft being fit to fly today. Reporting obligations sit on top of both.
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