Airtime calculation with Virb XE

Hi

I have a specific question:
I currently use a Virb XE. In addition to the "normal" data such as speed, g-forces, etc., the airtime (time in the air) in jumps can be visualized.

Now I have ordered the new VivoActive HR watch from Garmin with differend information can be recorded.
I play with the idea to create a similar app as Gravatron which records number of rides, Speed, jumps, etc. also the airtime.

Does anyone know how the airtime calculation has been solved in the Virb XE (which sensors are queried for / combined)?

Greeting
Markus

P.S.: Sorry for my bad english ;-)