Stewart Island Flights is a regional New Zealand airline offering scheduled and scenic flights from its base in Invercargill to Stewart Island. It is a locally owned and operated company. Stewart Island Flights was previously called Southern Air and then Southern Air 1997 Ltd. South East Air Ltd is the parent company and holder of the Air Operator Certificate, under which Stewart Island Flights and Invercargill Aircraft Maintenance are operated.
Stewart Island Flights has scheduled flights between Invercargill and Stewart Island, and are operated 3 x daily all year. Scenic flights operate on an ad-hoc basis around Stewart Island and Southland.  South East Air started an IFR post run from Invercargill to Dunedin and return on the 4th June 1996 using a Piper PA32 Cherokee.
Stewart Island Air Services / Southern Air / Amphibian Airways / Mount Cook / T.A.T originally operated a Grumman Widgeon amphibian from Invercargill to an alighting ramp in front of the South Seas Hotel in Stewart Island's main settlement of Oban, located in Half Moon Bay. This service was from 1951–1976, when Mount Cook, who bought the service off A.A, pulled out. Stewart Island Air Services took over in 1976, but the Widgeons were beyond their used by date. Salt water was really taking its toll. It was apparent, that the Island needed some sort of service set in concrete, literally.
March 1978 saw the Ryans Creek airstrip built and Stewart Island Air Services introduced the Britten - Norman BN2 Islander IAS. This type has remained the main aircraft in use ever since. Stewart Island Travel, owned and operated by Lloyd and Beryl Wilcox, met the aeroplane at the strip, taking passengers, animals, post, newspaper and food to town by the yellow Ford Transits before the days of the ferry (who now take all that), when Wairua came twice(?) weekly, which was not efficient. 1980, IAS crashes on the strip due to windshear. In 1981 Stewart Island Air Services changed its name to Southern Air. This is because they were expanding their routes to not only Stewart Island, but also Dunedin. Southern Air introduced its first turbo-prop type, the GAF Nomad N-22 ZK - SAL to replace IAS. Also, 2 Piper Aztecs were in service, DUB and TJE, along with Cessna 402 DSB, which operated the Dunedin run with SAL. However the Nomad proved too costly to operate as the tourist numbers were low, and it had extremely high maintenance costs. The Nomad had disappeared by 1983. The Nomad and Cessna 402 DSB were used operating the Dunedin route and with an extension to the Ryans Creek. This service operated from 1983-1983. In 1983, Southern Air went into receivership. It was bailed out by share holders, Keith Smith, Joe Cave, Bill Haslett and Sam Nicol. This was a big risk, because the passenger numbers were falling, and because of the lost profit the Nomad caused. Aztecs and 402 were gone, and Islander FGR was purchased in 1983, along with FFL 1984.
These aircraft were the backbone of the air link for the next 6 years. Keith realized that Stewart Island was not heard of New Zealand wide. This pushed him to promote the Island as a tourist attraction, not just the third Isle of NZ. Along with Stewart Island Travel, this hard work paid off, and is still apparent today. 1985 Islander FLU was brought bringing the total to three Islanders. Between 1985 and 1990, these seemed to be the busiest years on record - ever. 1989, Keith Smith along with Dick Langdon, saw the establishment of Southern Air's newest asset, Shearwater Inn. This provided accommodation for the backpacker, and tourist with a tight budget. New Islanders FXE and FWZ were brought 1991, to replace FFL and FGR which were sold by 1992, due to corrosion. 1991 also saw FLU out of service due corrosion, but was back on in the same year. 1990, Ryans Creek has the "hill" at the 22 end of the strip taken out. This gave more room for the Islanders to land and takeoff, with a 200m extension given. The road went on this extension now. 1993, Southern Air buys the Post office / depot to serve as a terminal for the waiting passengers. Southern Air brought its own vans, Hiaces and Bedford CF's to collect and drop passengers at Ryans Creek, so Stewart Island Travel was not needed, but continued offering bus tours of the Island till the late 90's. During the early 90's to the mid 90's, Live Fish and Lobster flights started. This saw the arrival of the Instrument arrival and track from Invercargill, and in reserve. 1993, Southern Air buys the South Seas Hotel. Keith did state he "was not going to take over the Island" as it would have seemed during these years (Ryans Creek airstrip, Depot / Post Office, Shearwater Inn), but more of committing Southern Air to the Island. This was sold mid 90's. In 1997 Southern Air was brought by Allan Aitcheson, who called it Southern Air 1997 LIMITED. Cessna 172P DNP and 177RG DXS were brought into service. 1998 saw the arrival of the ill fated Cessna 402 VAC and the depart of Islander FLU in 1998 also. Keith Smith died in 1999(?).