Boeing said it was cooperating with the investigations, but it would be premature to go into detail.

“However, nothing we’ve seen in this case indicates a relationship to any previous 787 power system events, which involved power panel faults elsewhere in the aft electrical equipment bay (where the fire occurred),” the company said.

The Wall Street Journal, citing a source, reported that United Airlines found improperly installed wiring in 787 electrical components associated with the auxiliary power unit, the same electrical system that caused Monday’s fire.

United spokeswoman Christen David said the carrier inspected its 787s after the Boston fire, but she declined to discuss the findings, or to confirm the Journal report.

The Federal Aviation Administration last month ordered all 787s to be inspected after fuel leaks were found on two aircraft, due, it said, to incorrectly assembled fuel line couplings that could result in power loss or an engine fire.

Mechanical problems are not uncommon when new planes enter service and they often disrupt airline schedules, experts said.

“I think we’re dealing here with a situation where this aircraft is over-scrutinized for a number of reasons, including the birth difficulties,” said Michel Merluzeau, managing partner at defense and aerospace consulting firm G2 Solutions.

“Don’t get me wrong. A battery fire is a very, very serious event. Especially a lithium-ion battery,” he added. “And we don’t know what the problem is. But the 787s is still a very safe aircraft to fly.”

(Additional reporting by Karen Jacobs in Atlanta, James Topham and Yoko Kubota in Tokyo, Anurag Kotoky in New Delhi, and Alison Leung in Hong Kong, Regan Doherty in Doha; Writing by Alwyn Scott and Ian Geoghegan; Editing by Andrew Hay and Will Waterman)