By Tim Hepher

PARIS, Aug 18 (Reuters) - Airbus has tentatively set the first flight of its delayed ‌A350F freighter for the third week of September ‌as it tries to loosen Boeing's grip on airborne trade, industry ​sources said on Tuesday.

The schedule, which could slip into early October, leaves the European planemaker with a finely balanced certification timeline as it aims to complete flight testing ‌and achieve the first ⁠delivery to customers before the end of next year.

Flight trials usually take 12 to ⁠15 months, industry sources say.

An Airbus spokesperson said it had nothing to add to its most recent predictions of ​a maiden ​flight before the end ​of this year, followed ‌by first delivery in the second half of 2027.

Originally launched in 2021 with a goal of entering service four years later, the dedicated freighter version of Airbus's A350 long-haul jet family aims to penetrate a corner of ‌the aircraft market long dominated ​by Boeing.

Airbus has sold 107 of ​the lightweight composite ​A350F cargo planes, compared with 38 of ‌a smaller and older A330F ​model.

Reuters reported in ​May that Airbus was facing delays in cargo doors built by Airbus in Spain for the new ​freighter.

Aviation publication ‌Leeham News reported this month that A350F deliveries ​could slip into 2028.

(Reporting by Tim HepherEditing by ​Susan Fenton and David Goodman)