Boeing has successfully completed the first test flight of the world's largest twin-engined plane, the 777X.

The 252-foot passenger plane had been due to launch this year but has faced a number of technical difficulties. 

A flight took off near Seattle and lasted four hours after two earlier attempts this week were called off due to high winds.

Further tests are needed before the aircraft enters service with Emirates next year.

309 planes, at $442 million each have been purchased so far as the company looks to go head-to-head with the Airbus models.