Bombardier has pushed back first flight of the CSeries again, from the end of this month, and now says the aircraft will fly “in the coming weeks”.

The first flight-test aircraft, FTV1, originally was planned to fly at the end of last year.

The company says integration of software upgrades and overall systems validation is taking longer than anticipated. The last delay, from the end of June, was attributed to incorporating additional software upgrades to improve system maturity and functionality.

FTV1’s Pratt & Whitney PW1500G geared turbofans and Honeywell auxiliary power unit are running, allowing on-aircraft testing of systems, says Bombardier. The aircraft has completed ground vibration testing and the next steps are low- and high-speed taxiing.

The delays will put pressure on plans to certify the 110-seat CS100 by mid-2014, although Bombardier says the increased systems-integration maturity will improve flight-test maturity. Five CS100 flight-test aircraft will be built.

“At this time our focus is on supporting first flight. The results following those activities will be reviewed and analyzed, and we will provide an update following that analysis,” says a Bombardier spokesman.

In the “aircraft in the loop” testing now under way, FTV1 is being “flown” on the ground in a simulated flight environment, to ensure the aircraft behaves in the same way as the on-ground complete aircraft integrated systems test rig, also known as Aircraft 0. “While the process has taken more time than we had expected, we are pleased with the results and are very comfortable taking more time to ensure the required integration is finalized and the CSeries is cleared for its first flight,” says Mike Arcamone, president of Bombardier Commercial Aircraft in a statement.

Bombardier says activities are progressing with Transport Canada to obtain the flight-test permit for FTV1, which is required before taxi tests begin as it is possible for the aircraft to become airborne during high-speed runs.