To expand on
grasscarp's earlier good answer... Samoa Air isn't actually an airline in the sense tha most are accustomed to. That is, they operate under what, here in the U.S. would be called 'Air Taxi' or 'Charter' rules, simply because they use much, much smaller airplanes.
Here's a quote from their website:
"...Samoa Air operates a fleet BN2A Islanders, and a Cessna 172 - The Islander is one of the best-selling commercial aircraft types ever produced in Europe, over 750 are still in service with commercial operators around the world. The excellent Short Take-off and Landing (STOL) performance of the Islander is well suited to the conditions and all airstrips in the Samoa Islands and the region."
Here's a picture of the BN2A 'Islander" aircraft:
http://www.planespotters.net/Aviation_Photos/photo.show?id=370574
They seat 9 passengers (pax in airline parlance) and fly about 120 MPH. Perfectly safe, but the weight limits are pretty severe when considering reserve fuel... even in good (Visual Flight Rules or VFR) weather. Hence, they can't use the standard "average" passenger weight limits that the larger aircraft are allowed to use.
The BN2A probably can carry about 2200 pounds or so of passengers, bags, cargo, crew (usually just one) and fuel. Fortunately, their leg lengths (take-off to landing) aren't that long... probably just a couple hundred miles at most...