Investigators are "probably weeks away" from completing their probe into battery problems on the Boeing 787 Dreamliner and will share their latest information about the jet today.
All 50 Dreamliners in service have been grounded since January 16, while the US National Transportation Safety Board, US Federal Aviation Administration and other regulators around the world investigate the battery failures that included one fire. No root cause has been identified.
"We will talk about special conditions that were put into effect at the time when the Dreamliner was certified," NTSB chairman Deborah Hersman said.
Fire risks on planes have always been a major concern, especially given the amount of fuel they carry and the heat generated by jet engines. US aviation standards require planes to have numerous on-board fire-suppression systems.
The FAA in 2007 granted the Dreamliner special conditions and said its contain-and-vent system was sufficient to control the build-up of explosive or toxic gases, except in situations considered "extremely remote".
That decision has come under scrutiny after the lithium-ion batteries in two 787 planes failed within days of each other, sparking a fire in one jet in Boston and generating warnings and an acrid smell that prompted the pilots of the second plane to make an emergency landing in Japan.
The NTSB is conducting the US probe with help from Boeing, battery maker GS Yuasa Corp of Japan, the FAA and battery experts from other US federal agencies, but none of the agencies has yet identified what caused the battery failures on the 250-passenger airliner.
Boeing this week asked the FAA for permission to conduct test flights of the 787, suggesting it is making progress, but the government agency has not yet announced a decision.
"In essence what happens when an aircraft is certified, it basically gets locked into the standards that are in existence at the time. So the question . . . is whether or not as time goes on through the life of the aircraft, do they fly with new standards?" Ms Hersman said.