The rechargeable batteries, widely used in consumer devices, have some pilots worried because batteries being shipped as cargo are suspected to have caused or contributed to the severity of fires in cargo planes.When Boeing proposed using the batteries in the 787, the Federal Aviation Administration issued special rules, including a requirement that they be designed to prevent overheating. The FAA noted in its 2007 rule that, "In general, lithium ion batteries are significantly more susceptible to internal failures that can result in self-sustaining increases in temperature and pressure. ... The metallic lithium can ignite, resulting in a self-sustaining fire or explosion." The severity of overheating is higher in larger batteries, the FAA said in the rule. The National Transportation Safety Board said it's sending an investigator to Boston. The Federal Aviation Administration also said it was investigating. Boeing Co. spokeswoman Lori Gunter said the company was aware of the fire and was working with JAL. She said she couldn't immediately answer other questions because Boeing's technical team was focused on the investigation. Boeing's stock fell $1.55 on Monday, or 2 percent, to $76.14. Boeing has delivered 49 787s, including seven to Japan Airlines. Another 799 have been ordered by airlines worldwide. Ed Freni, Massport's aviation director, said JAL officials reported that the plane that caught fire Monday was delivered to the airline in late December. JAL began nonstop service between Boston and Tokyo's Narita Airport using the Boeing 787 in April. A return flight to Tokyo was cancelled Monday and JAL was working to reschedule passengers, a JAL spokeswoman said. ___ Associated Press writer Joshua Freed in Minneapolis contributed to this report.