The airplane maker says it still doesn't know what the impact will be on the first delivery. Another delay is widely expected. Boeing says it will take a few more weeks to revise the schedule.
Boeing says it simulated key aspects of the fire in a laboratory, and is fixing the design.
Boeing spokeswoman Lori Gunter says the company doesn't know what the foreign object was. She says whatever it was burned up in the fire. Testing on the six airplanes stopped after the fire.
Boeing said it will present a plan to the Federal Aviation Administration soon to restart testing.