Boeing confirmed today that it will delay first flight of the 787 Dreamliner once again, from the end of the first quarter to around the end of the second quarter, due to what 787 program boss Pat Shanahan described as inaccurate assessments of the time needed to complete so-called traveled work in Everett, Wash. The delay will push the target for first deliveries into early next year from late this year and, according to Boeing Commercial Airplanes CEO Scott Carson, the company will not meet its previous target of 109 deliveries for next year.

Carson wouldn’t issue a new estimate, however, citing a desire to base any new projection on more hard facts gleaned from discussions with partners than on analysis based on assumptions. He said that Boeing would issue a new rate schedule for next year by the end of this quarter.

For his part, Shanahan identified traveled work on the fuselage–items such as wire routing and system rack installations–as the primary culprit and stressed that “parts are not a pacing item.” Rather, he said, the process of reconciling partners’ engineering work with Boeing’s design records hasn’t gone as smoothly or quickly as anticipated. Shanahan added that the wings “look good,” that engineers have finished incorporating any needed changes to the wire bundles that the oft-referenced fastener shortage has shrunk from more than 10,000 “down to the hundreds.”

Nevertheless, Carson acknowledged that the delays have “tested” Boeing’s credibility. “We are deeply disappointed by what this delay means for our customers, and we are committed to working closely with them as we assess the impact on our delivery schedules,” he said.

He and Shanahan both expressed confidence in the accuracy of the latest projections, now that the company has collected three months of empirical data and experience in performing the work in question since the last delay. “Our revised schedule is based upon updated assessments from the 787 management team of the progress we have made and the lessons we have learned to date,” said Carson. “This includes our experience on the factory floor completing production work on the airplane that was originally intended to be done by our suppliers.”