Two crashes within five months -- Lion Air Flight 610 in October off the coast of Indonesia and Ethiopian Airlines Flight 302 in March outside Addis Ababa -- killed a combined 346 people and led to a global grounding of Boeing Co.’s 737 Max jets. Numerous investigations are under way, including ones looking at how U.S. flight regulators came to certify the airplane. The Max is the fourth generation of a venerable brand -- Boeing’s 737 series, the world’s best-selling commercial aircraft, first flown in 1967.

1. How disruptive have the groundings been?

With many more Max jets in production than in service, not very. In the U.S., for example, the Max makes up about 3 percent of the mainline fleet. Southwest Airlines, a prime user, said the grounding is causing about 130 daily cancellations. Airlines have used other planes in their fleet or leased aircraft. Travelers have suffered little disruption, though there’s a risk ticket prices may rise, at least during peak season in some markets.

2. Which airlines were using the 737 Max?

The main operators include Southwest (31 in the fleet through February), American Airlines (24) and Air Canada (23). Chinese airlines account for about 20 percent of 737 Max deliveries globally. (Click here for the full list.) As of February, Chicago-based Boeing reported 376 deliveries of the single-aisle Max jets to 47 airlines or leasing companies, with orders from more than 80 operators for at least 5,000 more. 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.)

3. What caused the crashes?

A preliminary report by Indonesian authorities points to a malfunction of an anti-stall safety feature -- the Maneuvering Characteristics Augmentation System, or MCAS -- that repeatedly forced the Lion Air plane into a nosedive. Pilots commanding the doomed Ethiopian Air jet were hit with a cascade of malfunctions and alarms seconds after taking off from the Ethiopian capital on March 10, according to a preliminary report released on April 4. Critically, the plane’s automatic anti-stall system began pushing the nose of the jetliner down less than two minutes into the flight due to a malfunctioning sensor.

4. What is MCAS?

It’s a set of sensors and software that Boeing installed in the 737 Max to help pilots respond to a situation in which the wings are losing lift because the plane is climbing too steeply. (The use of new, bigger engines on the 737 Max required Boeing’s designers to mount the units farther forward on the wings in order to give them proper ground clearance when taking off or landing. That changed the plane’s flying characteristics.) Boeing said there was a simple procedure for shutting off MCAS. The day before the Lion Air crash, an off-duty pilot on the same aircraft correctly diagnosed the problem and told the crew how to disable the system, saving the plane.

Read more: A QuickTake on MCAS

5. Who approved this system?

The U.S. Federal Aviation Administration gave final certification to the 737 Max in March 2017. Under its Organization Designation Authorization program, established in 2005, the FAA delegated to certain Boeing employees the authority to perform safety-certification work on the FAA’s behalf. FAA employees warned as early as seven years ago that Boeing had too much sway over safety approvals of new aircraft. The Seattle Times reported that the safety report Boeing delivered to the FAA for MCAS had several flaws. The U.S. Transportation Department has begun an inquiry into how MCAS was approved, and the Justice Department is using a grand jury to gather information for possible criminal action.

6. What can be done now?

Following the October crash, the FAA said it would mandate proposed MCAS changes by Boeing to make activation less likely when there is no emergency. Boeing has been working on software updates that the FAA would have to approve before the Max 737 flies again. The agency and Boeing said they also will require enhanced pilot training and additional references to the MCAS system in flight manuals.

7. What does this mean for Boeing?

As the company’s largest seller, the 737 accounts for almost one-third of operating profit. Lion Air and several other carriers have suspended deliveries of the 737 Max or put orders on hold. Norwegian Air said it will seek compensation for the grounding of about 1 percent of its seats. There’s also the prospect of substantial payouts to the families of passengers if Boeing is found responsible for the crashes. In the week after the second crash, Boeing lost more than $22 billion, or 12 percent, of its market value. Boeing issued a statement after the U.S. regulator grounded the aircraft saying it still has “full confidence” in the plane. Boeing has suspended customer deliveries and is cutting monthly output to 42 from 52

--With assistance from Paul Geitner, Alan Levin and Laurence Arnold.

To contact the reporter on this story: Kyunghee Park in Singapore at

To contact the editors responsible for this story: Jon Morgan at, Grant Clark

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