A Boeing 787 Dreamliner took to the sky earlier this week in a test flight to test the plane's new lithium-ion battery system.
The roughly two-hour flight, which Boeing said "went according to plan", lacked the crowds that cheered the 787's maiden journey in 2009.
But if found successful, the test flight will allow Boeing 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 all 50 Dreamliners in mid-January after batteries overheated on two separate aircraft, one parked at the Boston airport and the other forced to make an emergency landing in Japan.
Earlier this month, the FAA agreed on tests Boeing would conduct to return the plane to service.
Resuming flights would be a relief for Boeing, which is losing an estimated $50m a week while the 787 is grounded.
Airlines in Japan, the United States, the Middle East, Europe and Africa that bought the fuel-efficient jet but are barred from using those planes are also suffering.
Boeing is still building 787s, but cannot deliver them to customers during the grounding.
Some Boeing officials have said the jet could be back in service by 1 May, or earlier.
But Oliver McGee, an aerospace and mechanical engineer who was a deputy assistant secretary of transportation under President Bill Clinton, said he was sceptical that regulators would allow service to resume so soon.
"Take whatever date is agreed upon and add three to six months to it," McGee said.
"I don't think that you're going to see any type of quick fix or compromising on the FAA side."
McGee said the trauma of the Columbia and Challenger shuttle disasters would make federal officials reluctant to sign off on the new battery system until they were absolutely sure it would work as Boeing promised.
The U.S. National Transportation Safety Board set a two-day forum for 11-12 April to examine the design and performance of lithium-ion batteries in transportation - a comprehensive review sparked by the twin battery failures in January.
The NTSB also plans to hold a separate hearing on the 787 battery later in April.
The test flight, the first with Boeing's new battery system, took off on Monday at approximately 1211 Pacific time (1911 GMT) from Paine Field in Everett, Washington, on a planned two-hour mission designed to validate that all systems on the plane are working as designed.
Live video showed the jet, with LOT Polish Airlines livery, soaring into a clear sky with snow-capped mountains in the distance.
It flew south down the west coast of Washington and about half way down the coast of Oregon before turning back to Paine Field, according to flight tracking website Flightware.com.
It made a loop out the Strait of Juan de Fuca at low altitude and speed, then turned back toward the airport.
The flight landed at 1420 Pacific time, and the flight crew reported the test "went according to plan", Boeing said in a statement.
Once data from the flight has been analysed, Boeing said it would prepare for a ground and flight demonstration aimed at certifying the company's proposed changes to the battery system.
The system is made by Thales SA of France, and the battery is made by Japan's GS Yuasa.
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 15 March.
The tests are being conducted in labs, in planes on the ground, and in flight.
"Obviously, progress is being made on all three fronts," Birtel said.
Despite uncertainty about when the FAA will approve Boeing's new battery system, some experts said the revamped unit is likely to prove successful.
Former NTSB Chairman Mark Rosenker said Boeing has invested hundreds of thousands of engineering hours to develop the improved battery system.
"They don't want to put an airplane up that they're going to have to deal with again," he said.
"They want this thing resolved. They want to do it in an efficient, appropriate, scientific, analytic way. It is not in their best interests to rush a system."
John Goglia, a former NTSB board member, said he expects the steel containment box will work as expected, and the plane could be returned to service in April.
"I will give the Boeing engineers the benefit of the doubt that they have designed a box that will handle what the battery can give it," he said.