Until when did a converted Sunderland fly commercially?

A more refined civilian conversion of the Sunderland was completed by the manufacturer itself as the post-war Short Sandringham. The Sandringham Mk. I used Pegasus engines, while the Mk. II carried Twin Wasps. Converted Sunderlands began operating with BOAC on its route between Poole Harbour (Dorset) and Lagos, Nigeria, in March 1943. In 1946 BOAC acknowledged that its flying boat fleet was insufficient for all the routes it envisaged and placed its first order for the Sandringham. The following year, the Sandringham 5 entered service with BOAC, which the company called the "Plymouth class" and used mainly on its Far East routes from Southampton, via Alexandria, to Hong Kong and Tokyo.

The New Zealand airline TEAL was another early Sandringham operator, using it mainly on the Auckland-Sydney route and on flights to various Pacific islands. In 1950 Qantas introduced the first of five aircraft flying from the Rose Bay flying boat base in Sydney Harbour to destinations in New Caledonia, the New Hebrides, Fiji, New Guinea and Lord Howe Island; two of them were bought from TEAL and the other three from BOAC. Qantas kept them in scheduled service until 1955.

Ansett Flying Boat Services used the Sandringham on the scheduled service from Sydney (Rose Bay) to Lord Howe Island until 1974. One of the last operators of the Sandringham was Antilles Air Boats, in the Caribbean's Virgin Islands, which flew it in scheduled passenger service until the 1970s.