WASHINGTON – While Boeing maintains that a fire in an electronics compartment of Boeing's 787 Dreamliner last week and another fire on a test flight in 2010 are not related, the plane's fire-suppression system does not protect the site where both fires occurred.

The incidents have some aviation experts questioning assurances by company officials, the Federal Aviation Administration and Transportation Secretary Ray LaHood that the plane is safe.

The National Transportation Safety Board is investigating last week's fire, and the FAA is reviewing the plane's electrical system and the inspection process that led to the plane's certification in 2011. The Dreamliner relies on its electrical components more than any similar aircraft, and much of that system is supplied by UTC Aerospace.

The Charlotte, N.C., company also furnishes the plane's fire detection and suppression system, which uses Halon 1301 gas to extinguish fires in cargo compartments, but not the one that contains key electrical systems.

A spokesman for UTC Aerospace directed questions about the plane's design to Boeing.

Boeing spokeswoman Lori Gunter said that fire-suppression systems are not typical in electronics compartments.

"That's not unique to the 787," she said. "It's true of all Boeing airplanes."

Though production of Halon 1301 has been banned for most uses for nearly two decades because it depletes ozone, it still is commonly used in fire-suppression systems on aircraft. Barry Chase, a fire protection engineer at the National Fire Prevention Association in Quincy, Mass., said that another common use in the past was to protect computer rooms.

"It's not electrically conductive," he said. "It was used that way for a very long time."

Last week's fire in Boston took 40 minutes to extinguish and damaged a lithium-ion battery that powers the plane's auxiliary power unit, according to the NTSB. The plane was empty at the time, but one firefighter suffered minor injuries.

The 2010 fire occurred in midair and damaged one of the plane's primary electrical-distribution panels. Backup systems allowed the crew to safely make an emergency landing in Laredo, Texas, and evacuate the 42 people on board. The problem was traced to a metal shaving that caused a short-circuit in the panel, and Gunter said changes were made to the plane's software to cut power quickly in case of a short.

Boeing grounded its test fleet after the fire, adding to delays that had plagued the program from its inception.

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