Bombardier has pushed back first flight of the CSeries by up to a month to allow for additional software upgrades and ground testing. The first flight-test vehicle (FTV1) is now planned to fly “by the end of July”.

This is the second slippage, and follows postponement of first flight to the end of June from December 2012 because of delays in final assembly and system testing for the all-new narrowbody.

The latest delay follows completion of ground vibration tests “as well as software updates and corresponding tests,” Bombardier says. The company is not revealing which systems are involved, but says software updates to improve “system maturity and functionality” do not include the fly-by-wire flight controls.

There were signs first flight would slip. Speaking at last week’s Paris air show, the head of a major CSeries supplier said meeting the end-June date would be a challenge for Bombardier, but expressed confidence that, if first flight did slip, it would be a matter of weeks, not months.

The aircraft manufacturer has now applied to Transport Canada for its permit to fly FTV1. Power runs, low-speed and high-speed taxi lie ahead for the aircraft before its first flight from Mirabel, Quebec, near Montreal.

Bombardier is building five flight-test aircraft for certification of the initial 110-seat CS100, which is still scheduled to enter service mid-2014. FTV2 through 5 are expected to follow FTV1 into flight test at roughly monthly intervals.

Another two flight-tests aircraft are in construction for certification of the 135-seat CS300, which is expected to enter service at the end of 2014.