RIYADH, Aug 21 (Reuters) - Saudi Arabia plans to transfer ownership of all its airports to its main sovereign wealth fund, the Public Investment Fund, as part of a drive to privatise them, a senior aviation official said on Monday.

Companies will be set up for each airport under Saudi Civil Aviation Holding, a spin-off from the General Authority of Civil Aviation (GACA), which will continue to regulate the industry, state news agency SPA quoted Mohammed al-Shetwey, aide to GACA's president for financial affairs, as saying.

"The process of establishing companies will continue for all airports, and the civil aviation holding company in the future will be 100 percent owned by the Public Investment Fund," Shetwey said.

He added that a company had already been established for Dammam's main airport, while an expanded King Abdulaziz International Airport in Jeddah would start operating in the second half of 2018 under the management of Singapore's Changi Airport Group.

Shetwey did not say when or how the Public Investment Fund would sell stakes in the airport companies under the privatisation programme.

However, sources told Reuters last month that Saudi Arabia had hired Goldman Sachs to manage the sale of a stake in Riyadh's King Khalid International Airport, which would be the first major privatisation. The size of the stake to be offered was not revealed.

Shetwey said a project to refurbish that airport, which handled 22.5 million passengers in 2016, would begin after next week's haj pilgrimage.

(Reporting by Stephen Kalin; Editing by Andrew Torchia and Richard Balmforth) ((stephen.kalin@tr.com; +971 52 322 9759; Reuters Messaging: stephen.kalin.thomsonreuters.com@reuters.net))