Ministers have launched a consultation on plans to cut air passenger duty (APD) in Scotland.

APD is being devolved from Westminster to Holyrood, where the administration has committed to halving the rate from 2018.

Under the SNP's plans, the 50% reduction would begin in April that year and be delivered in full by the end of the next parliament in 2021.

The tax would be abolished completely when resources allow, ministers have said.

The Scottish Government launched a consultation on its reform plans on Monday, and claimed the tax was among the most expensive of its kind in the world.

APD is charged on all passenger flights from UK airports, and the rate of tax varies according to the passenger’s destination and class of travel.

The government is seeking views on how the reduction should be structured and how the tax should be operated to help boost Scotland's "economic competitiveness".

The consultation will run for 12 weeks until June 3.

Launching the plan at Edinburgh Airport, Deputy First Minister John Swinney said APD "continues to act as a barrier" to Scotland's ability to secure new direct international routes - and maintain existing ones.

He said: "Scotland is already an attractive destination for business and inbound tourism, and it is important that we continue to open Scotland up to key and emerging markets in order to further capitalise on the opportunities that exist.

"We want to be consultative and collaborative, as we have been with the new fiscal levers already devolved to Scotland.

"This policy consultation allow us to take the next step and begin the process of developing a new approach that helps deliver our objective of sustainable economic growth."

Edinburgh Airport's chief executive Gordon Dewar described APD as a "regressive tax that hampers growth".

Amanda McMillan, chief executive of AGS Airports Ltd, which owns both Aberdeen and Glasgow airports, said: "APD is the highest form of aviation tax in the world and its reduction, and eventual abolition, will undoubtedly play a major role in strengthening Scotland's connectivity."

Views are also being sought on the environmental issues which need to be considered.