(Reuters) - More than 300 Boeing 737 MAX 8 and MAX 9 passenger jets have been grounded worldwide after two fatal crashes in the past five months in Ethiopia and Indonesia killed nearly 350 people.

FILE PHOTO: Boeing 737 MAX aircraft are parked at a Boeing production facility in Renton, Washington, U.S., March 11, 2019. REUTERS/David Ryder/File Photo

Investigators looking to uncover the causes must answer one of the biggest questions: Was the plane’s software to blame?

WHAT WE KNOW

- Europe and Canada said they would independently certify the safety of the jets, further complicating plans to get the aircraft flying.

- Boeing has stopped delivery of all new MAX jets to its customers. Stock losses have wiped around $28 billion from its market value since the Ethiopian Airlines crash.

- Boeing maintains its new, fuel-efficient jets are safe, but supported the U.S. Federal Aviation Administration (FAA) decision to ground them.

- Investigators have found strong similarities in the ‘angle of attack’ data from both flights. A piece of a stabilizer in the wreckage of the Ethiopian jet with the trim set in an unusual position was similar to that of the Lion Air plane, sources said.

- Investigators who verified data from the black box recorders of the Ethiopian plane have found ‘clear similarities’ with the doomed Lion Air flight, French air accident authority BEA has also said.

- Experts believe a new flight control system, MCAS, on the jets, designed to stop stalling by dipping the nose, may have been a factor in both crashes, with pilots unable to override it as their jets plunged. But no conclusive evidence yet links the two accidents.

- The pilot of the Ethiopian flight had reported internal control problems and received permission to return. The pilot of the Lion Air flight, which crashed on Oct. 29 with the loss of all 189 aboard, had also asked to return soon after take-off from Jakarta.

- Sources with knowledge of the doomed Lion Air cockpit voice recorder revealed how pilots scoured a manual in a losing battle to figure out why they were hurtling down to sea.

- Communications showed that in the final moments, the Lion Air captain tried in vain to find the right procedure in the handbook, while the first officer was unable to control the plane.

- Indonesia has advanced the date for the release of its report on the Lion Air crash to between July and August, versus a previous schedule of between August and September.

- Boeing’s commercial airplane division has brought in a new vice president of engineering while dedicating another top executive to the aircraft investigations, a company email showed.

WHAT’S NEXT?

- Boeing plans to release upgraded software for its 737 MAX in a week to 10 days, sources familiar with the matter said on March 16.

- U.S. lawmakers said the planes could be grounded for weeks to upgrade and install the software in every plane. Other countries may ground the planes even longer.

- The U.S. Transportation Department’s inspector general plans to audit the FAA’s certification of the jet, an official with the office said on Tuesday. The office can recommend changes or improvements to how the FAA operates.

- The U.S. Justice Department is also looking at the Federal Aviation Administration’s (FAA) oversight of Boeing, one of the people said. The FAA has said it is “absolutely” confident in its vetting.

- The chairman of the U.S. House of Representatives transportation committee and another key Democrat asked the Transportation Department’s inspector general to examine key decisions the FAA made in certifying the MAX jet for use.

- U.S. President Donald Trump will nominate former Delta Air Lines executive Steve Dickson to head the FAA, the White House said.

- Ethiopian Airlines said on March 16 that DNA testing of the remains of the passengers may take up to six months.