The £285m airport dubbed “the world’s most useless” is finally going to get a scheduled flight – but no-one knows when, nor how much flights will cost.

St Helena airport was built at UK taxpayers’ expense to provide a lifeline for the remote south Atlantic community. Despite warnings about tricky weather conditions, the runway was constructed to allow passenger jets such as the Boeing 737 and Airbus A320 to land.

After a series of construction delays, plans were announced for a regular scheduled service in British Airways colours from Johannesburg in South Africa, carrying around 170 passengers. But shortly before the planned royal opening in May 2016, a test flight revealed severe wind shear.

The airport has since been used for a number of medical evacuation flights, and in May this year a passenger test flight was successfully handled.

The island’s government has now announced that a South African carrier, Airlink, will fly from Johannesburg via Windhoek in Namibia to St Helena each Saturday. But no start date has been announced, and neither have fares for the subsidised service been revealed. The UK Government will subsidise the operation up to £1.9m in the first year of operation, representing over £36,000 per return flight – or nearly £500 per available seat.

Because of safety limitations, a maximum of 76 of the 99 seats on the Brazilian-built Embraer jet will be occupied. The lower weight will allow it to use a shorter stretch of runway, avoiding the portion where rapidly changing winds are most common.

The overall flight time from Johannesburg will be over six hours, more than an hour longer than the originally planned non-stop service. The schedule requires the plane to leave Johannesburg minutes before the first of five arrivals from Heathrow, and return to the South African hub too late for connections on any of the five evening departures to London.

Dr Niall O’Keeffe, chief executive for economic development, Enterprise St Helena, said: “Scheduled air services is what is needed to build a sustainable tourism industry on St Helena.

“As a remote small island developing state, the onset of air services is crucial to enable the development of a sustainable economy in the long-term. The opportunities for tourism and investment as the island opens up as the newest air destination in the world, cannot be overstated.”

The island’s director of tourism, Christopher Pickard, said: “As much as we are going to miss the RMS, not everyone has two weeks to travel to and from the island by ship.”

On the second Saturday of each month the flight will continue on from St Helena for a further 800 miles to Ascension Island, where it will remain overnight.