I've been trying to identify this show for a while, however my memories of it are fuzzy.
I watched it at some point between 2003-2012, likely on one of the following channels in England: CBBC, CITV, CBEEBIES (unlikely but possible). It may also have been on other non-Sky channels at the time. It didn't look out of place aesthetically, so I assume its from roughly that time, however it could have been older.
I recall that a family, I think(?) -- I believe there was a sister and brother + more -- travelled on a sky ship between sky islands. If it had a main storyline, it was incomprehensible by the airing schedule. There is one scene that sticks in my mind, however.
In one episode, the sister takes part in some sort of martial arts (the name skyfu comes to mind, but that may have been a joke in the show?) challenge that I believe was some sort of kata rather than a fight; it at least seemed like one. During this, they run at each other, then jump and essentially run into the air by pushing off from each other's feet, with it basically being a mirror. This came off as a really dumb scene, even for child me.
I don't believe that it's Skyland or Storm Hawks, having skipped through them / checked their wiki pages, but may be wrong.