Between Norddeich, Germany and the Island of Juist there are between 6 and 10 daily scheduled flights. The distance is about 10km and the flight time listed as 5 minutes. I couldn't find information about flight numbers or plane types.
There are also a large number of on-demand and sightseeing flights out of Juist airport, allegedly making this tiny runway the second-busiest airport (by number of flights) in the state of Lower Saxony.
Juist is a very popular health spa and tourist destination, but the ferry schedule has to change with the tides, so going there by plane is often the most convenient option.
As an added curiosity, cars are not allowed on the island, so the shuttle service between the airport and the two towns is provided by horse carriage.