The Chicago Tribune reported Saturday that a Goldman Sachs analyst warned in a research report Friday that Boeing may not turn on all of the plane's electrical systems for the first time until the end of June rather than the end of March.
"In our view, Boeing continues to underestimate the amount of work required on the 787," Goldman analyst Richard Safran wrote.
He said the plane's wiring problems have proven time-consuming and difficult to resolve, the newspaper reported.
Boeing officials said the Chicago-based company is assessing the 787 Dreamliner program.
"Boeing is in the process of conducting an assessment of its 787 delivery schedule and will communicate it to customers around the end of first quarter, as previously indicated in January," Boeing spokeswoman Yvonne Leach said.
Boeing was supposed to deliver its first 787 Dreamliner to launch customer All Nippon Airways in May. That first delivery to the Japanese airline now likely won't happen before mid-2009, Safran said.