Boeing Co said it would resume tests for the carbon-composite 787 Dreamliner later on Thursday after it made design changes following an electrical fire on a plane last month.

The company said in a statement it has installed an interim version of updated power distribution system software and conducted a rigorous set of reviews to confirm the flight readiness of the first of the six flight test airplanes that will resume flying.

Boeing said it expected to complete its assessment of the 787 program schedule next month. Another delay in the first delivery of the 787 is widely expected.

Flight testing of the 787 was suspended last month after an in-flight electrical incident on a test flight in Laredo, Texas. Certification tests required by aviation regulators will resume after flight tests, the company said.

The first delivery of a 787, to Japan's All Nippon Airways <9202.T>, is already nearly three years behind schedule.

Delivery of the Dreamliner, which promises hefty fuel savings to airlines, has been delayed six times because of problems with engineering and with Boeing's global supply chain. Labor unrest, including a 58-day strike that shut the company's Seattle plants in 2008, has also contributed to the delays.

Boeing, the second-largest commercial plane-maker after Airbus , has said foreign debris probably caused the November 9 fire that erupted as Dreamliner test plane ZA002 approached the Laredo airport. The wide-body made an emergency landing and the more than 40 people aboard exited safely.

The company's first-quarter delivery target will slip, Boeing's commercial aircraft chief said last month. Outside estimates expect a delay of at least a few months.

Boeing made six test planes, of which three are solely for testing and three will eventually be sold and enter passenger service.

Boeing shares gained 0.7 percent to $65.06 on the New York Stock Exchange.

(Reporting by Nick Zieminski and Karen Jacobs; Editing by Steve Orlofsky)