The Sikorsky-Boeing SB-1 Defiant’s first flight will likely be delayed until early 2019 after “minor” problems were discovered within the aircraft’s testbed.

Until a few weeks ago, the SB-1 Defiant demonstration helicopter was on track to achieve first flight in 2018. However, discovery of unnamed issues on the powertrain system test bed, which must be fixed before the aircraft takes to the skies, caused the delay.

The two companies are now focusing on implementing fixes so the test bed can start running again within one or two weeks.

The aircraft was supposed to have flown for the first time last year, but issues with the composite rotor blade manufacturing process delayed take off.

Delays to the SB-1’s first flight come after its chief rival, the Bell V-280 Valor tiltrotor, has been flying for about a year and in May achieved a top speed of 190kt (352km/h).