One program manager later acknowledged that Comac simply was inexperienced in that process, despite having gone through it about six years earlier with its ARJ21 regional jet.
Industry sources close to the program remain skeptical about the new target; suppliers also are known to be expecting first deliveries in 2018, not 2016.
A strong sign that things were not going well emerged in April when it was revealed that Comac had switched the material for the center wing box, the structural heart of the aircraft, from carbon-fiber composite to aluminum.
Industry sources at the time said the change was made because the manufacturer saw too much risk in building the composite part. Another industry source now says that the problem was that the composite center wing box, built with foreign help, would have cost too much.
To some extent Comac was ready for the change, because early in its program it decided to develop aluminum alternatives to composite parts.
Development of the aluminum center wing box should have been well advanced when the decision to use it was made.