A Boeing 787 Dreamliner took to the sky Monday in the first of two flights aimed at showing that the plane’s new lithium-ion battery system meets regulatory safety standards. (Christopher Furlong/Getty Images)

A Boeing 787 Dreamliner took to the sky Monday in the first of two flights aimed at showing that the plane’s new lithium-ion battery system meets regulatory safety standards, a key step toward ending a two-month worldwide grounding of the high-tech jet.

Boeing said Monday’s roughly two-hour flight test “went according to plan.” If successful, it would allow the company to go ahead with a second flight test “in coming days” that would gather data to be submitted to the Federal Aviation Administration to certify the new battery system, Boeing spokesman Marc Birtel said.

The FAA and other regulators grounded the Dreamliner in January after batteries overheated on two separate aircraft.

Resuming flights would be a huge boost for Boeing, which is losing an estimated $50 million a week while the 787 is grounded, and for airlines, which are barred from flying the 787. Boeing also is prevented from delivering the planes to customers during the grounding, though it continues to build them.

Some Boeing officials have said the jet could be back in service by May 1. But some experts cautioned it could take longer.

Oliver McGee, an aerospace and mechanical engineer who was a deputy assistant secretary of transportation under President Bill Clinton, said he was skeptical that federal regulators would allow the 787 to resume flights as early as May 1.

“Take whatever date is agreed upon and add three to six months to it,” McGee said in an interview. “I don’t think that you’re going to see any type of quick fix or compromising on the FAA side.”

The first test flight took off Monday at 12:11 p.m. Pacific time from Paine Field in Everett, Wash., to validate that all systems on the plane are working as designed. Video of the event showed the jet, with LOT Polish Airlines markings, soaring in a clear sky with snow-capped mountains in the distance.

It flew south down the west coast of Washington and about halfway down the coast of Oregon before turning back to Paine Field, according to the flight-tracking Web site FlightAware. It made a loop out the Strait of Juan de Fuca at low altitude and speed, then turned back toward the airport.

Once data from the flight has been analyzed, Boeing said it would prepare for a ground and flight demonstration aimed at certifying the company’s proposed changes to the battery system.

Boeing plans to conduct one certification demonstration flight using the same LOT plane, Line Number 86, to show that the new battery system performs as intended during flight conditions. The system includes a steel box designed to contain a battery explosion and prevent fire, as well as a tube to vent fumes and heat out of the aircraft.

Birtel said it wasn’t clear if the demonstration test for the FAA would conclude Boeing’s testing of the new battery system, which was unveiled in Tokyo on March 15. The tests are being conducted in the laboratory, in planes on the ground and in flight. “Obviously, progress is being made on all three fronts,” Birtel said.

Separately, the National Transportation Safety Board on Monday said it would hold a forum April 11-12 to examine the design and performance of lithium-ion batteries in transportation — a comprehensive review sparked by the battery failures on the two Boeing 787 Dreamliners.

The public forum will examine the design and development of various lithium-ion batteries, how their use and manufacturing are regulated, and the use and safety of such batteries in various modes of transportation.

The FAA grounded all 50 Boeing 787s in use worldwide in January after failures of two batteries on two aircraft — one parked at the Boston airport and the other forced to make an emergency landing in Japan.