Charts expire on a schedule.
Aeronautical data worldwide moves on the AIRAC cycle: a new effective date every 28 days, thirteen times a year, every state publishing its changes to take effect on the same day. The synchronisation is the whole point — controllers, charts, databases and autopilots all flip together, so that nobody negotiates a boundary using last month's sky.
Your flight computer joins that agreement the day you load a current file, and silently leaves it 28 days later. Nothing on the screen changes to tell you — the polygons still draw, the warnings still fire, everything looks exactly as authoritative as it did in March. The date is the only tell, and the instrument will show it to anyone who looks.
Three files, three failure modes.
The airspace file fails as infringements: a control zone extended, a new drop zone, a changed frequency — flown into with last season's polygons and full confidence. The turnpoint and airfield file fails on the ground: a runway resurfaced and renumbered, an airfield closed, a fuel service gone. The obstacle file fails at the worst possible altitude: the new mast on a familiar ridge, exactly the kind of thing you stopped looking for years ago.
They age at different speeds — airspace changes every cycle somewhere, turnpoints drift by seasons, obstacles rarely but decisively — and each is a separate download with its own date. The habit that works treats them as one set: refresh together, verify the three dates together on the instrument afterwards.
How stale is your map?
The λ slider is how much of the world's churn actually touches the airspace you fly in — boundaries, frequencies, obstacles on your routes. At half a relevant change per cycle, a card barely six weeks old is already a coin flip — and a card from last season is not "probably fine", it is a 95% certainty that something you trust has changed.
Firmware is a database too.
Instrument firmware carries data formats, warning logic and — in the case of FLARM — a deliberate expiry date: the radio protocol evolves, and a unit too many versions behind eventually stops being understood by the fleet around it. That is a feature, not an insult; it guarantees the collision-avoidance conversation stays mutual.
The discipline for firmware is the same as for data, plus one rule of timing: update at home, over coffee, with the release notes read and the settings backed up — never the evening before a competition, and never at the launch point on a data cable balanced across a wing. A firmware update is a small maintenance action; treat it with the same respect as one.
In your cockpit.
Modern systems make the hygiene nearly effortless: one card carries all the files, one status screen shows every version and age, and a platform with its own connectivity updates the databases over the aircraft's connection without the card ritual at all. What no system automates is the decision that currency matters — that the sky on the screen should be this month's sky. That one stays yours.
What those boundaries mean once they are current — classes, floors, and the warning that arrives in time — is the airspace article.