Two crashes within five months -- Lion Air Flight 610 in October 2018 off the coast of Indonesia and Ethiopian Airlines Flight 302 in March outside Addis Ababa -- killed 346 people and led to a global grounding of Boeing Co.’s 737 Max jets, the fourth generation of a venerable brand first flown in 1967. Uncertainty over when it will fly again is rippling through the airline industry and Boeing’s finances. The U.S. manufacturer’s bill is $9.2 billion and rising, as it faces questions about the plane’s development and its own transparency.

1. When will the 737 Max fly again?

Unclear. Boeing says the U.S. Federal Aviation Administration is on track to certify redesigned flight-control software by mid-December, but the Max won’t be cleared to resume commercial flights until regulators also sign off on updated training material for pilots -- a step Boeing expects in January. It also will take time for airlines to ready stored jets for service and work them back into flight schedules. Two of the largest operators of the Max, Southwest and American airlines, have removed it from their flight schedules through early March. Europe’s top aviation regulator expects to take longer to get the plane back into service than in the U.S.

2. Will air travelers get back on board?

At least 20% of U.S. travelers said they would definitely avoid the plane in the first six months after flights resume, according to an April 2019 survey led by consultant Henry Harteveldt. More than 40% said they’d even take pricier or less convenient flights to stay off the Max. UBS Group AG’s most recent survey about the 737 Max found 12% of respondents saying “no amount of safe operation will alleviate their concerns” about flying on the plane. To boost public confidence, American says its executives and other staff will take the first flights, before paying passengers, as soon as the Max is certified fit to fly.

3. What has this meant for the airline industry?

Far more jets were in Boeing’s order backlog than in service. But the impact has piled up. Ryanair Holdings Plc is scaling back growth plans for mid-2020 because, it says, it’s likely to get barely half of the 58 Max planes it was expecting. American said it’s canceling about 140 flights a day; at Southwest, that number is 200 on an average weekday. TUI AG, the world’s largest tourism service company, said a profit rebound was wiped out by the grounding of its 15 Max aircraft. The hit to Boeing’s suppliers could be far worse if the company follows through on warnings it might halt production. CFM International, a joint venture between General Electric Co. and Safran SA, cut output by at least 5%, while Safran says it may lower its earnings forecast.

4. What has this meant for Boeing?

In April, the Chicago-based company abandoned its financial forecast for 2019 and missed its quarterly earnings estimates for just the second time in five years. Its shares have tumbled and in the third quarter, it posted its largest cash burn in almost 25 years. Boeing revealed in July that it had taken a $5.6 billion pretax writedown to cover potential costs incurred by airline customers due to the grounding; already, Indian budget carrier SpiceJet Ltd. has booked income it expects to receive as compensation. Saudi Arabia’s Flyadeal in July became the first airline to officially drop the 737 Max, reversing a commitment to buy as many as 50. Virgin Australia has pushed back delivery of its first 737 Max jets by almost two years. In addition, there’s the prospect of substantial payouts to the families of passengers if Boeing is found responsible for the crashes.

5. Any fallout at the top?

Some. The head of Boeing’s jetliner division, Kevin McAllister, stepped down. Chief Executive Officer Dennis Muilenburg was stripped of his role as chairman and will waive his 2019 bonus. He faced a grilling by U.S. lawmakers and numerous calls to resign during two days of often contentious hearings in October. At a conference a week later, he said he considered stepping down but decided to stay on.

6. What legal action could Boeing face?

Claims have been filed by families of crash victims. Bloomberg Intelligence estimates Boeing’s litigation risks in the U.S. could amount to $1 billion. Boeing has offered $100 million over several years as an “initial outreach” to support the families of victims and others affected, and hired high-profile mediator Kenneth Feinberg to distribute it. On other legal fronts, the U.S. Justice Department expanded its probe to include a look into manufacturing of another Boeing aircraft -- the 787 Dreamliner -- at a new plant in South Carolina. The U.S. Securities and Exchange Commission is investigating whether Boeing properly disclosed issues tied to the 737 Max jetliners to investors. And Boeing faces proposed class action lawsuits by pilots.

7. What does Boeing say?

Muilenburg, who was criticized for a subdued initial response to the tragedies, has apologized for the accidents and said the situation “will continue to weigh heavily on our hearts and on our minds for years to come.” The company has said it thinks the 737 Max will eventually regain its position as the backbone of its single-aisle fleet.

8. How many 737 Maxes are out there?

Before the crashes, Boeing reported 387 deliveries of the single-aisle Max jets to 48 airlines or leasing companies, with orders from around 80 operators for 4,406 more. Southwest says it has 34 in its fleet. Other major operators include American (24) and Air Canada (24). Chinese airlines account for about 20% of 737 Max deliveries globally. Most sales are the Max 8, the model involved in both crashes. (There’s also, from smallest to biggest, a Max 7, 9 and 10.)

9. What do people think caused the crashes?

In both cases, pilots were likely overwhelmed by a new flight control feature added to the Max known as the Maneuvering Characteristics Augmentation System, or MCAS. It activates when the plane appears to be at risk of stalling, a situation in which the wings are losing lift because the jet is climbing too steeply. The use of new, bigger engines on the 737 Max required Boeing’s designers to mount the turbines farther forward on the wings to give them proper ground clearance. That changed the plane’s center of gravity. In the two crashes, MCAS kicked on due to an erroneous sensor reading and pushed the plane’s nose downward. After a rocky trial of the MCAS software in 2016, one senior Boeing pilot called the handling performance “egregious.” The crash report by Indonesia’s National Transportation Safety Committee also blamed a failure to adequately consider the human equation and how pilots respond to a fast-moving emergency in a chaotic cockpit.

10. Who approved this system?

The FAA gave final certification to the 737 Max in March 2017, and it entered commercial service two months later. Under a program established in 2005, the FAA had delegated to Boeing the authority to perform some safety-certification work on its behalf. Some FAA employees warned as far back as 2012 that Boeing had too much sway over safety approvals of new aircraft. Boeing said in May that it had known months before the Indonesia crash that the cockpit alert wasn’t working the way it had told buyers, but it didn’t share that with airlines or the FAA until after the Lion Air jet went down.

--With assistance from Alan Levin and Anurag Kotoky.

To contact the reporters on this story: Kyunghee Park in Singapore at kpark3@bloomberg.net;Julie Johnsson in Chicago at jjohnsson@bloomberg.net

To contact the editors responsible for this story: Brendan Case at bcase4@bloomberg.net, ;Young-Sam Cho at ycho2@bloomberg.net, Laurence Arnold, Paul Geitner

©2019 Bloomberg L.P.