SEATTLE — Boeing Co. will not begin test flights of its new 787 jetliner until mid-November or mid-December, months later than originally planned, because it's taking longer than anticipated to get the first plane ready, the company said last week.

Boeing initially aimed to begin flight testing within a monthlong window beginning in late August, but early last month acknowledged first flight might not happen until October.

The midsized, long-haul 787 is the first large commercial jetliner being made mostly from composites, which Boeing has promised will make the plane more fuel efficient and cheaper to maintain because carbon fiber-reinforced plastics are lighter and more durable than aluminum.

On Wednesday, Scott Carson, chief executive of Boeing Commercial Airplanes, said the first flight test will be pushed well into the fall because of delays in completing assembly of the first plane and in finishing software.

Even so, Carson and Mike Bair, vice president and general manager of the 787 program, said the company has contingency plans in place to keep the 787 on track to be delivered to its first customer, Japan's All Nippon Airways, next May.

In a conference call with analysts and reporters, Carson declined to discuss possible penalties Boeing might have to pay if any planes are delivered late, but said, "A one- to three-month delay would have minimal financial implications for us in '08."

Rival Airbus SAS's A380 superjumbo has suffered about two years of delays, in large part because of wiring problems, which have wiped billions off its parent company's profit forecasts for the coming years.

Boeing unveiled its first 787 amid much fanfare in early July, but has spent the past several weeks working to get that plane ready for its maiden flight.

Boeing had large sections of the first aircraft delivered to the final assembly plant before they were stuffed with electrical wiring and other systems — work that will eventually be done by suppliers. Having that "travel work" handled by in-house mechanics has proved more complicated than expected, in some cases because Boeing has had to clear up errors in documents its suppliers have sent, Bair said.

Boeing recently told suppliers to reschedule some work and take on more of the systems installation so the company can streamline final assembly.

"Sorting through and understanding the facts and rescheduling the work accordingly has taken some extra time," Bair said.

The company also hired new mechanics and made others available to do the final assembly work once those components arrive at the factory, Bair said.

Boeing has had to grapple with replacing thousands of temporary fasteners that hold the plane together with permanent ones — a time-consuming problem brought on because of an industrywide shortage of the tiny parts, some of which are unique to the 787.

Mechanics still have to remove and replace hundreds of temporary fasteners on the first plane, Bair said.

Boeing has done a lot of pre-flight testing on the 787 that has helped it find and fix problems it normally wouldn't discover until the flight-test program is under way. Still, Bair said, surprises could cause setbacks.

The 787's flight-test program will be more condensed than that of Boeing's last all-new jet, the 777, which went through about 11 months of flight testing before entering service in 1995.

To get the airplane certified on time, Bair said, the company plans to fly six fight-test 787s at higher rates — about 120 hours a month — than it has with previous planes, which have flown about 70 to 80 hours a month. Two other planes will undergo static and fatigue tests on the ground.