If it doesn't explicitly say STM on the lens, then it's not that version. But it should work anyway.
Your EF-S 55-250 mm f/4-5.6 IS doesn't have any IS mode selector switch. It does have IS mode 2, though, but the mode selection is done automatically by the lens. IS mode 2 is a mode that's specifically desgined to work better when panning a subject, i.e. following its path, keeping it in your viewfinder as it passes by. Just like an anti aircraft gunner would do, you just fire less lethal shots, even when you actually have a Canon!
Use Servo AF, continuous drive mode and one AF point to begin with. Start tracking the aircraft prior to taking photos of it, by tracing it with the viewfinder whilst keeping the trigger button half-pressed. Then fire as you see fit, but never release the trigger button fully, but just to the half-pressed position. Thus you keep on tracking focus even when not shooting. Keep on tracking/panning after taking the last picture of a fly-by, as that will make your photos steadier. When tracking aircrafts on a bly sky you can also use all AF points at the same time with reasonable success. Start with the center point on your camera model. The camera can then hand over focus tracking to another point, should you fail in keeping the center point on the target all the time. That's easy to do.
To keep on focustracking between shots is easier to do when you can keep a button fully pressed, rather than having to remember not to let go fully of the trigger button. This is what back button focusing is about. For cameras with AF-ON button, just keep that pressed. You don't have to remove focusing from half-press for this purpose. Cameras lacking the AF-ON button requires the * button to be reassigned from being AE lock to AF ON.
