Two separate problems have been identified in the gear boxes, requiring the aircraft to undergo regular inspections and to have parts replaced if necessary, Airbus said.

One issue was with the material structure and strength of the ring gear in about 14 gear boxes produced in the first half of 2015. The other problem was cracking of a plug that could see small parts of metal released into the oil system of the gearbox, affecting gear boxes that rotate to the right.

However Airbus stressed that the aircraft, which have four propeller engines, can fly normally.

"We continue to aim for 20 deliveries this year, counting on EPI and Avio to bring the adequate solutions to the propeller gear box issue in the necessary timeframe," Fernando Alonso, Head of Military Aircraft at the Airbus Defence and Space Division, said in a statement to Reuters.

EPI is the engine consortium for the A400M and Italy's Avio provides the power transmission for the engine.

The A400M programme has been beset with delays and Airbus is currently working on a revised delivery schedule for this year.

Airbus has already delivered two A400Ms to Britain this year.

(Reporting by Victoria Bryan and Gernot Heller; Editing by Clelia Oziel)