Which flight is that?
Tap a plane on the map and the card has always been headed by something like DLH441. That string is the callsign — what the pilot says on the radio and what air traffic control writes down. It is also, in most cases, the flight number, just written the way controllers write it rather than the way your boarding pass does. DLH441 is Lufthansa 441. BAW117 is British Airways 117. UAE47 is Emirates 47.
So the answer to "which flight is that" was on the card the whole time, in a notation almost nobody outside aviation reads. Now the card says both: the callsign stays as the title, and underneath it a line reads Flight LH441. The same line appears on the radar card after a scan, and on the full data plate that pops up when you fly within nine kilometres of an aircraft in the simulator.
Where it comes from
Nowhere new. ADS-B — the signal aircraft broadcast and our feeder network receives — carries the callsign, and we already keep a table of airlines that maps the three-letter prefix DLH to Lufthansa and its two-letter code LH. Putting those together is one string operation on your own machine. No new data source, no external request, no cost, nothing extra sent over the wire. The information was sitting in two halves and nobody had joined them.
Why some aircraft still won't show one
A callsign only equals a flight number when everything after the airline prefix is digits. Several carriers deliberately fly alphanumeric callsigns that are not the commercial flight number at all — Ryanair's RYR7HW, easyJet's EZY43UK. There is no flight FR7HW; that combination exists only inside the air traffic system. The real number for those flights lives in airline schedule databases, which is a different and considerably more expensive kind of data.
When we can't convert it honestly, we show nothing rather than a plausible- looking guess. You still see the callsign in the title, so nothing is lost — you just don't get a second line claiming to be something it isn't. The same goes for general aviation, where the callsign is usually the aircraft's registration, and for private traffic, which we deliberately show without any identity at all.
What's next
The obvious follow-up is where the aircraft is actually going. That one is genuinely not in the signal — ADS-B broadcasts position, altitude, speed and identity, but never a route. Connecting a callsign to "Houston to Frankfurt" means a flight database, and the good ones cost money and come with real terms about what you may store. We've done the research and written it down; whether it ships depends on whether this turns out to be something you actually want on the card, or just something that sounded good on paper.
If you have an opinion, the Discord is the place.