Obama administration officials struggled Wednesday to defend their initial statements that the Boeing 787 is safe while promising a transparent probe of mishaps involving the aircraft’s batteries.

Transportation Secretary Ray LaHood stood by his Jan. 11 assertion that the 787, Boeing’s newest and most technologically advanced airliner, was safe. At that time, LaHood and the head of the Federal Aviation Administration, Michael Huerta, declared the plane fit to fly despite a battery fire in one plane.

Five days later, following another battery mishap that led to an emergency landing of a 787 in Japan, LaHood and Huerta ordered United, the lone U.S. carrier with 787s, to ground the planes. Authorities in other countries swiftly followed suit.

“On the day we announced the planes were safe they were,” LaHood told reporters at an aviation industry luncheon. He became testy when a reporter pressed him on whether his initial pronouncements had been too hasty.

“I’m not doing these hypothetical look-backs,” he said. “We did what we did.”

What changed between Jan. 11 and FAA’s issuance of a grounding order on Jan. 16 was that a second battery failure occurred on an All Nippon Airways 787 while the airliner was in flight, said Huerta, who joined LaHood at the luncheon. In the first incident, the battery fire occurred in a Japan Airlines 787 that had already landed at Boston’s Logan International Airport and was empty of passengers.

“We took the action we took (to ground the planes) because we saw a hazard,” Huerta said.

FAA is working as quickly as possible to find the cause of the problems, assembling a team of technical experts that includes experts from industry as well as the agency’s staff, Huerta said. The review includes not just the 787’s ground-breaking lithium-ion battery system, but how that system works with the aircraft’s electronic systems, their certification, manufacture and assembly, he said.

“We don’t know yet what caused these incidents yet. When we know the cause we will take appropriate action,” he said.

The officials emphasized that the investigation would be completely transparent so that the public will have confidence in the outcome.

LaHood denied that Boeing had asked the government to lift the grounding order.

“Absolutely not,” he said. “Boeing is cooperating 100% with the review.”