Bombardier is still struggling with the all-composite airframe of the new Learjet 85 business jet, which is moving toward a delayed first flight.

In December, the Canadian manufacturer pushed back the Learjet 85’s entry into service by six months to summer 2014 because of delays in assembling the aircraft in Wichita.

By mid-March, the first Learjet 85 was in the second-to-last assembly station before first flight, Guy Hachey, president and CEO of Bombardier, told investors last week.

“We do still have some issues,” he said. They are not with the aircraft’s systems, as might be expected, he said, but with its all-composite structure – Bombardier’s first.

“We are inventing as we go, and that is where the challenges have been biggest versus the systems, which are not so aggressive and leverage the Global Vision,” he said, referring to the new flight deck developed for Global-series business jets.

Bombardier’s biggest challenge has been in perfecting the all-composite fuselage, which is a single piece from nose to rear pressure-bulkhead – “It is one-part number,” he said.

Developing the fuselage, which uses new out-of-autoclave composite technology, took longer than planned. “It was very painful, but we have fixed it,” he said.

The lingering problem is “in making the parts in volume, repetitively” as fuselage production ramps up at Bombardier’s plant in Queretaro, Mexico.

The composite wing, produced at Bombardier’s plant in Belfast, Northern Ireland, has not been a struggle, Hachey said, because it uses the same resin transfer molding technology as the CSeries airliner wing.

The Learjet 75, meanwhile, is on track for entry into service in the second half of this year, he said. The Learjet 70/75 family is a revamp of the Learjet 40/45 with updated avionics, a redesigned cabin and uprated engines to improve field performance and range.

The range-topping Global 7000 and 8000 ultra-large, long-range jets are close to exiting the joint definition phase, Hachey said, aiming for service entry in 2016 and 2017, respectively.

“These are not high-risk aircraft because of our Learjet 85 and CSeries learning,” he said, adding “They are fly-by-wire, but we will have done CSeries by then.”