WASHINGTON -- Boeing has asked the Federal Aviation Administration for approval to resume test flights with the 787 Dreamliner while the plane remains grounded for an investigation of battery faults.

The FAA was considering the request yesterday, an agency official said. Boeing would operate any such flights with existing test aircraft, Marc Birtel, a company spokesman, said. He wouldn't say when or where Chicago-based Boeing might conduct any tests, or with how many planes.

Flying test planes would let Boeing study the Dreamliner's lithium-ion power packs while the 50 in service stay parked. Regulators and Boeing are still trying to determine what caused a battery fire on one jet and a cockpit warning that spurred an emergency landing by another, which in turn triggered grounding orders worldwide on Jan. 16.

Boeing, which has its commercial hub in Seattle and also builds 787s in North Charleston, S.C., performed thousands of hours of tests on the six-jet development fleet before the jet's 2011 commercial debut.

Safety officials outside the United States joined the FAA's order to airlines to park their Dreamliners following a fire in the lithium-ion power pack of a Japan Airlines 787 in Boston and a battery warning on an All Nippon Airways flight that forced an emergency landing.

The Seattle Times first reported Boeing's request. -- Bloomberg News

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