You mean, the smallest airline in term of the one with the lesser regular flights ?
Here in CMF, we've got Hex'Air : just one bi-daily CMF-ORY flight (so the 'fleet' is airborne less than 4 hours per day) with their one and only jet - an ERJ135.
Okay, they also have a King Air 90 and an Beech 1900for charter flights, but does that count ?
Oh, and sometimes if they don't have enough pax to fill the ERJ, they use one of the smaller planes
Small airline indeed, but I've got to love them, otherwise I wouldn't have this bi-daily jet...