You can now catch the airliner right above you
Here is the report that started this. A pilot circles over Frankfurt, and a Ryanair 737 MAX at FL380 crosses straight overhead. They raise the zoom, put the crosshair on it and hold. Nothing happens. The lock ring never starts and the only text on the screen is «Aim at a vessel».
That pilot did nothing wrong. Until today an aircraft could only be caught within 9 km of the camera, measured in a straight line. FL380 is about 11.6 km up. A gull flying at 700 m was still more than 10.9 km from a jet passing dead overhead, so every airliner at cruise was out of reach from anywhere in the world. You could catch them on approach or climbing out of an airport, and never at cruise.
The game also contradicted itself about it. The strip above the reticle, the one that shows which way to turn, measures distance along the ground. It listed the same jet as a target «6.2 km» away while the lock refused it.
What changed
Range is measured along the ground. An aircraft is catchable when it is within 9 km of you horizontally, however high it flies. Low traffic behaves exactly as before, because at low altitude the two distances are almost the same. High traffic overhead is now in reach. The strip and the lock use the same rule, so whatever the strip offers, you can lock.
Height still costs time. The lock still takes longer for distant aircraft, and that part of the rule still uses the straight-line distance. A jet at FL380 overhead takes the full two and a half seconds of holding steady, not the quick lock you get on a light aircraft at low level.
Out of range is spelled out. Aim at an identified aircraft that is beyond reach and the reticle turns grey, with «Too far» and «Catch within 9 km horizontally» under it. The chip below shows the callsign and how far away it is. Press the shutter anyway and you get the exact numbers. The ship spotter no longer answers «Aim at a vessel» while you are clearly pointing at the sky.
What did not change
Private aircraft still cannot be caught, because they carry no identity to claim with. The once-a-day rule per airframe stands. Zoom is still required. The catch range itself is still 9 km. The only change is the direction we measure it in. The labels in the sky are untouched as well: the full plate with a photo still appears within 9 km in a straight line, and farther contacts keep their compact tag.
If you were saving up cruise traffic for a lucky approach, go look up. The busy corridors over Frankfurt, Amsterdam and London carry hundreds of jets an hour, and your collection has room for them.