In a statement released this morning, the company says that while "significant progress has been made assembling Airplane #1," the first flight is being rescheduled, due to "slower than expected completion of work that traveled from supplier facilities into Boeing's final assembly line, unanticipated rework, and the addition of margin into the testing schedule."

The new schedule is "based on a more conservative production plan developed with the 787 partner team," the company statement says.

The company is about to start a conference call with analysts and reports to explain the decision.