Bombardier Aerospace commercial deliveries continue to lag, down by almost half so far this year as the company begins testing on the new CSeries line in preparation for first flight this year.

The airframer delivered 22 commercial aircraft in the first six months of the year, nearly half the 43 delivered in the fiscal first half of 2011. In the second quarter, deliveries fell to 15 from 20 in 2011. Bombardier says the decrease in deliveries is due to “lower production rates to reflect current demand.” In addition, some deliveries were pushed to the second half of the year. Bombardier expects to deliver 55 commercial aircraft this year.

Bombardier has taken orders for 40 commercial aircraft during the first half of this year, a slightly slower pace than the 48 taken in the first fiscal half of 2011. Most of this year’s orders came in the first quarter; Bombardier recorded 12 orders in the second quarter.

But Bombardier President and CEO Pierre Beaudoin maintains that the commercial aircraft families are gaining momentum, particularly “outside traditional markets.”

He also was encouraged by progress on the CSeries, which is targeted for first flight by year-end. Most of the systems have been installed and are running on Aircraft “0,” and testing of those systems is expected to begin this month.

Those tests will be used to validate the systems on the ground before first flight.

Beaudoin, however, is cautious about the first flight timeline, noting the complex nature of the program–Bombardier’s first complete fly-by-wire aircraft–and says he would still consider the program on track even if first flight were to slip three to five months. “One challenge in an aircraft program like this is what you don’t know,” he says.

Business jet sales, meanwhile, continue to prop up Bombardier Aerospace’s business, accounting for the increase in revenues to $2.265 billion in the second quarter this year from $2.085 billion in 2011. For six months, however, revenues fell to $3.764 billion from $4.273 billion. That decline in part was due to the slowing of Global business jet deliveries in the first quarter; however, it expects to continue to ramp up Global deliveries in the second half as it sticks to its estimate of 180 deliveries for the year.