The standard tourbillon design
A standard tourbillon mounts the cage between two bridges: one underneath and one across the top of the cage. The upper bridge is a metal bar spanning the cage, providing structural support and keeping the cage axis fixed. From above, the bridge partially obscures the cage rotation, especially at the top of the carousel.
What 'flying' means
A flying tourbillon removes the upper bridge entirely; the cage is supported only by a lower pivot. From above, the cage appears to float free with no visible support, hence 'flying'. The mechanical challenge is making the lower pivot strong enough to keep the cage steady without an upper anchor; the cage axis must stay perfectly vertical despite the unsupported top.
Why it matters
Visual: the unobstructed view of the spinning cage is more dramatic. Mechanical: there's no functional advantage; both designs perform identically for rate. Historical: Alfred Helwig developed it in 1920 at the Glashutte watchmaking school as a teaching exercise; the technique was used in German pocket watches through the 20th century. The wristwatch revival came with the modern Glashütte Original and AP / Breguet haute-horlogerie pieces from the 1990s onward.
Modern flying tourbillons
Glashütte Original Senator Tourbillon and Pano Tourbillon carry the German tradition. Audemars Piguet Royal Oak Concept Flying Tourbillon. Breguet Classique Tourbillon Extra-Plat. Modern brands typically badge a tourbillon as 'flying' explicitly when the upper bridge is absent; standard tourbillons usually market simply as 'tourbillon'.