DOHA, Aug 31 (Reuters) - Qatar Airways plans to make a major aircraft purchase, its chief executive said on Wednesday, to meet fleet expansion plans and boost its global network. Akbar Al Baker did not comment on the details of the order, nor on which manufacturer the Gulf carrier would purchase the aircraft from.

"We expect to announce a large order soon," he told reporters at a briefing by the airline.

Qatar Airways has a continuous programme of fleet expansion and replacement, "to keep the average age of the fleet very young," he added.

Earlier this year the airline declined to take delivery of three Airbus A320neos -- part of a deal for 80 jets which Baker has said could be in jeopardy due to engine cooling issues. These have prompted the carrier to explore the option of switching to Airbus rival Boeing's BA.N 737 Max.

Qatar Airways said in July it was in advanced talks with Boeing to buy up to 30 narrowbody planes.

Airbus is also struggling to keep up with deliveries to Qatar of long-haul A350 planes which, combined with the A320neo's problems, has left Qatar Airways at risk of posting a loss in the fiscal year that ends in March, Al Baker said.

"Our relationship is very strained," he said. "What's happening at Airbus with the deliveries is seriously affecting our growth."

Unlike other airlines which are scaling back expansion plans due to flagging demand, Qatar is aggressively increasing its fleet despite an oil-induced downturn in Gulf economies.

However, the carrier has said its premium traffic yields have slipped in the face of weaker business sentiment and a drop in spending in oil producing nations.

(Reporting by Tom Finn; Editing by Alexandra Hudson) ((Tom.Finn@thomsonreuters.com;))