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

FILE PHOTO: People walk past a part of the wreckage at the scene of the Ethiopian Airlines Flight ET 302 plane crash, near the town of Bishoftu, southeast of Addis Ababa, Ethiopia March 10, 2019. REUTERS/Tiksa Negeri/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

** Boeing has stopped delivery of all new MAX jets. Its stock has fallen 7.5 percent 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.

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

** Boeing will mandate on MAX jets a previously optional cockpit warning light, which might have warned of problems that possibly played a role in the Ethiopian and Indonesian crashes, sources said on March 21.

** Indonesia’s flag carrier Garuda said on March 22 it had sent a letter to Boeing asking to cancel an order for 49 MAX 8 aircraft, becoming the first airline to confirm plans to cancel an order after the crashes.

** Investigators have found 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.

** 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 after a faulty sensor indicated a stall. But no conclusive evidence yet links the two accidents.

** The MCAS system on the Ethiopian flight re-engaged as many as four times after the crew initially turned it off, two people familiar with the matter told Reuters on April 3.

** The Wall Street Journal reported on April 3 that the Ethiopian Airlines pilots had initially followed Boeing’s emergency procedures but later deviated from them as they tried to regain control of the plane.

** 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?

** Ethiopia is due to publish the preliminary results of an accident investigation within days.

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

** U.S. lawmakers said the 737 MAX could be grounded for weeks to upgrade 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 March 19. The office can recommend changes or improvements to how the FAA operates.

** The U.S. Justice Department is also looking at the FAA’s oversight of Boeing, a person familiar with the matter has 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.

** U.S. President Donald Trump will nominate former Delta Air Lines executive Steve Dickson to head the FAA, the White House said on March 19.

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