Boeing Company announced the third major delay on its 787 Dreamliner on Wednesday, pushing back its expected debut in commercial service to the third quarter of 2009 as it continues to deal with slow progress on assembly and continuing problems with supplies. The newest delays push the 787's schedule back another six months and mean that the aircraft promoted by its potential to be more fuel efficient than other large jets is now 15 months behind its original schedule. The first test flight now is not expected to happen until the fourth quarter of this year as Boeing builds more time into the schedule to reduce the risk of further delays. “Our revised schedule is built upon an achievable, high-confidence plan,” Boeing Commercial Airplanes chief executive Scott Carson said in a statement. The company initially had planned to begin test flights last August or September and deliver the first jetliner to Japan's All Nippon Airways this May. Boeing recently rescheduled that delivery to early 2009. The newest delay of the 787, coming less than three months after the last one, further undermines Boeing's credibility on the much-hyped program and also is a setback to the more than 50 airlines that have placed almost 900 orders for the top-selling airplane. Buyers are likely to seek compensation for the delays. The company said that while significant progress has been made assembling the first airplane, it is rescheduling the first flight “due to slower-than-expected completion of work that traveled from supplier facilities into Boeing's final assembly line, unanticipated re-work, and the addition of margin into the testing schedule.” Boeing said it now expects to deliver only 25 of the new airplanes by the end of 2009, less than a quarter of its previous plan to deliver 109. The 787, the company's first newly designed jet since airlines began flying the 777 in 1995, will be the world's first large commercial airplane made mostly of carbon-fiber composites, which are lighter, more durable, and less likely to corrode than more traditional aluminum. Boeing says it will be cheaper to maintain and offer greater fuel efficiency and more passenger comforts than comparable aircraft flying today.