Here it is: Papeete-Moorea: distance 18km, duration 15mn, operated by Air Tahiti.

From [Air Tahiti site (fr)][1] (select "Tahiti" on "Ile de départ" and "Moorea" on "Ile d'arrivée"), there are several flights each day (VT266, VT240, VT444). 

But nothing can beat the Scottish 2.7km suggested by VMAtm!

  [1]: http://www.airtahiti.aero/horaires.php