Boeing said Wednesday it has "extreme confidence" in its 787 Dreamliner even as federal investigators try to determine the cause of a fire that has prompted new worries about the plane.

The fire happened Monday in one of the plane's lithium ion batteries. Mike Sinnett, Boeing's chief engineer for 787, wouldn't comment on that specific incident, but told reporters that the battery is designed to avoid overheating and the area around the battery is designed to withstand a fire.

But questions remain about the high-profile jet, which has a lot riding on it both for Boeing and its airline customers. After a nearly three-year delay, Boeing has delivered 49 of the 787s so far, and has about 800 more on order.