The Federal Aviation Administration, which must certify new planes as safe, is also investigating what caused the fire.

Hans J. Weber, an independent safety consultant, said if the fire stemmed from a flaw in basic electrical components, the problem could be relatively easy to fix. But if it were linked to more advanced electrical controls that help the Dreamliner save fuel, that could require more time-consuming changes. The plane’s development has been marred by persistent problems with Boeing’s far-flung supply network. Company executives have acknowledged that they farmed out too much design and production work and did not initially keep close enough tabs on suppliers.

But even though they have made an all-out push to meet their latest delivery schedule, more problems have cropped up over the last several months.

A Rolls-Royce engine meant to be used in one of the 787 test planes failed in a test plant in Britain in August, spewing out debris.

Boeing cited that engine problem in saying it would push back delivery of the first Dreamliner for the fifth time, from late this year to February 2011. Rolls-Royce has said it is confident it can fix the engine by that date.

Rolls-Royce also said this week that the problem on the engine for Boeing did not seem to be related to the failure last week of another Rolls-Royce engine on an Airbus A380 jumbo jet. That engine jettisoned debris while the plane, operated by Qantas Airways, was in flight.

Boeing has had to tell suppliers around the world to halt parts deliveries three times this year because Alenia Aeronautica, a unit of Finmeccanica of Italy, could not deliver the 787’s horizontal tails on time. The latest parts delay occurred in late October. Boeing officials have said that poor workmanship by Alenia and other suppliers forced Boeing to rework many parts, further slowing its production line.