SEATTLE/LONDON－Boeing will provide airlines that have bought the 737 Max jetliners with free software upgrades, the US manufacturer said on Monday, as Ethiopian Airlines told Reuters it expected a preliminary crash report this week or next.

Any fixes to the Max software, the focus of investigations of two deadly crashes that have prompted worldwide groundings of the aircraft, must still win approval from governments around the world.

The US Transportation Department said on Monday it is forming an outside panel to review the aircraft certification program of the Federal Aviation Administration, or FAA, amid growing concerns following two fatal Boeing 737 Max crashes.

The causes of separate Lion Air and Ethiopian Airline crashes are also still unknown, though Ethiopian Airlines Chief Executive Officer Tewolde Gebremariam said he trusts Boeing.

"Despite the tragedy, Boeing and Ethiopian Airlines will continue to be linked well into the future," Tewolde said on Monday. "Ethiopian Airlines believes in Boeing. They have been a partner of ours for many years."

The 737 Max is Boeing's best-selling plane, with orders worth more than $500 billion at list prices.

Meanwhile, Boeing has begun briefing airlines on software and training updates for the Max, with more than 200 global airline pilots, technical experts and regulators due this week in Renton, Washington, where the plane is built.

The sessions follow a briefing with carriers including three US airlines on Saturday, part of Boeing's effort "to communicate with all current, and many future, Max customers and operators", a Boeing spokeswoman said.

Tewolde said the leading African airline had not yet decides whether to attend the briefing.

Lion Air Managing Director Daniel Putut said his airline would send two people on Wednesday, a pilot and an engineer.

The crash of an Indonesian Lion Air flight in October killed 189 people and first brought the safety of the 737 Max into focus.

Boeing's shares closed 2.3 percent higher at $370.46 on hopes that a fix is nearing completion, but have lost about 12 percent and $29 billion in market value since the March 10 crash.

Boeing's fix for the grounded 737 Max will prevent repeated operation of an anti-stall system at the center of safety concerns, and deactivate it altogether if two sensors disagree widely, two people familiar with pilot briefings said.

The system ignited a debate over the proper balance between man and machine in piloting the latest version of the 50-year-old 737.

Upgrading an individual 737 Max with Boeing's new software only takes about an hour per plane, though the overall process could stretch on far longer as it is rolled out across the global fleet due to stringent testing and documentation requirements by engineers and regulators, according to a senior FAA official with knowledge of the process.

"Clearly there is pressure to get the airplanes ungrounded but there is tremendous pressure to make sure it was done right," the FAA official said. "The last thing in the world you want is to have the thing hurried and then find problems with it."

Ethiopian and French investigators have pointed to "clear similarities" between the two crashes, putting pressure on Boeing and US regulators to come up with an adequate fix.

No direct link has been proven between the crashes but attention has focused on whether pilots had the correct information about the "angle of attack" at which the wing slices through the air.

Reuters