The Ethiopian Airlines plane that crashed shortly after takeoff Sunday morning was a Boeing 737 Max 8, the same model operated by Lion Air that crashed off Indonesia in October. Federal investigators, Boeing, and airlines around the world are all seeking answers to what went wrong.

While it is too early to know what caused the Ethiopian Airlines crash, the fact that both planes went down shortly after takeoff has raised questions about the safety of the new 737 Max 8. In a statement Monday, Boeing said it had "engaged our customers and regulators on concerns they may have" and that "safety is our number one priority."

Ethiopian Airlines confirmed both of the plane's "black boxes," the flight data and cockpit voice recorders, had been recovered.

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Ethiopian Airlines grounded its fleet of Max 8s Monday, saying, "Although we don't yet know the cause of the accident, we had to decide to ground the particular fleet as (an) extra safety precaution."

Here are some answers to questions about the plane and what happened in the Lion Air and Ethiopian Airlines crashes.

What is the Boeing 737 Max 8?

The Boeing 737 Max 8 is a narrow-body passenger aircraft that was launched by Boeing to counter rival Airbus' best-selling A320. For Boeing the main feature of the 737 Max 8 was that the larger engines would require less fuel, thus increasing savings.

How long have they been in the air?

The first commercial flight of the 737 Max 8 was May 22, 2017, for Malindo Air, operating from Kuala Lumpur to Singapore. Southwest Airlines took its first delivery for its 737 Max 8 on Aug. 29, 2017, and debuted the plane Oct. 1, 2017.

How many are used in fleets around the world?

Boeing says it has delivered roughly 350 737 Max airplanes worldwide. The company says it has taken more than 5,000 total orders for the latest generation of 737s.

Which airlines use Boeing 737 Max 8 planes?

In the U.S., there are at least 69 Boeing 737 Max 8 aircraft in service across Southwest Airlines, American Airlines and United Airlines. After the most recent updated count, Southwest Airlines had 34 Max 8 aircraft, and American had 24. United said Sunday it has 14 Max 9 planes, which is a larger version of the same aircraft. Other major carriers around the world include Aerolíneas Argentinas, Air China, Icelandair and LOT Polish Airlines.

Which countries are grounding Boeing 737 Max 8s?

A mounting number of nations and individual airlines have decided unilaterally to ground their Boeing 737 Max 8 jets in the wake of the second crash.

Airline safety authorities in the European Union, the United Kingdom and a dozen other nations have now grounded the plane while the investigation continues.

Indonesia grounded all Boeing 737 Max 8 planes for inspection following the Ethiopian Airlines crash. There are currently 11 Max 8 planes operated by airlines in Indonesia including 10 by Lion Air and 1 by national carrier Garuda.

China has 96 Max 8 jets in service, belonging to carriers such as Air China, China Eastern Airlines and China Southern Airlines. The civilian aviation authority directed the planes to be grounded indefinitely on Monday. It said the order was "taken in line with the management principle of zero tolerance for security risks."

Australia announced a temporary ban on flights into or out of the country by Boeing 737 Max aircraft, although none of its own airlines currently operate them. The Civil Aviation Safety Authority said Tuesday that the ban would affect two foreign airlines, SilkAir and Fiji Airways, that use them for flights to Australia.

On Tuesday, an official with South Korean airline Eastar Jet said the two 737 Max aircraft in its fleet would be replaced by Boeing 737-800 planes from Wednesday. She said the airline hadn't found any problems, but was voluntarily grounding Boeing 737 Max 8s in a response to customer concerns. She says the planes will not be used until the completion of a government safety review on the aircraft.

Aeromexico, Brazil's Gol Airlines, India's Jet Airways, Cayman Airways and others also temporarily grounded their Max 8s.

How do I know if I'm flying on a 737 Max 8?

Most airlines inform passengers of the type of aircraft when booking a flight online or over the phone. Websites like SeatGuru and FlightStats can show the type of plane model for a specific flight. According to The Points Guy, American Airlines' Max 8 planes have row numbering systems that differ from traditional 737s.

A shot of Boeing's 737 Max 8 airplanes from the company's website. Eric Greer/Boeing

I keep hearing about "MCAS." What is MCAS?

The Max is outfitted with bigger, more fuel-efficient engines than earlier 737s, a change that shifted the center of gravity forward and increases the potential for the nose to pitch up after take-off. Boeing created software known as the Maneuvering Characteristics Augmentation System, or MCAS, to counteract this risk.

MCAS uses sensors to point the nose of the plane down if it detects it has pitched too high and could be at risk of stalling. By measuring the position of the plane's wings relative to airflow, the system's sensor indicate to pilots if the plane is at risk of stalling from going too slow or flying too steeply into a climb. It's a brand new system on 737 Max planes.

However, problems can arise when the MCAS system automatically pushes the plane's nose down, potentially surprising pilots who are unfamiliar with the system and overriding their commands. According to The New York Times, Boeing and the FAA decided pilots did not need to be informed about the change to the flight control system. The Times reported Boeing and regulators decided against informing pilots at least in part to minimize the costs of retraining pilots.

What happened in the Lion Air crash?

Lion Air Flight 610 crashed 12 minutes after taking off from Jakarta on Oct. 29, 2018. The pilots immediately had trouble controlling the pitch of the plane once it was in the air. A preliminary report by Indonesian investigators concluded the pilots repeatedly struggled to raise the nose of the plane during the short flight, at one point telling air traffic control they were flying manually and were unable to determine their altitude.

Authorities haven't settled on a final cause for the crash, but investigators discovered the sensor used to trigger the MCAS was replaced the day before the crash after experiencing problems on the four flights preceding the deadly crash.

After the crash, Boeing and the FAA indicated that the plane's MCAS system may have triggered the anti-stall system and overrode the pilots' manual controls, thus pitching the plane's nose downward. Boeing told The New York Times the pilots of Lion Air might have had the chance to steady the plane had they followed previously established emergency procedures used to control 737s in similar situations.

What happened in the Ethiopian Airlines crash?

Ethiopian Airlines Flight 302 took off from Addis Ababa, Ethiopia, Sunday morning, bound for Nairobi, Kenya. There were no irregular weather patterns and visibility was clear, according to flight data from FlightRadar24. But once in the air, the flight's vertical speed was unstable. The pilot sent out a distress call and was given clearance to return to the airport, but air traffic controllers lost contact with the plane and it crashed about six minutes after takeoff, the airline's chief executive said Sunday.

Ethiopian farmer Malka Galato told the Reuters news agency that he saw the plane crash onto his land. He said he saw small pieces of paper-like debris coming from the plane and that it was making an unusual noise and turned suddenly just before it crashed. Another farmer told Reuters that the doomed jet appeared to try to climb before making a sharp turn and slamming into the ground.

The plane went down 35 miles outside of Addis Ababa, and all 149 passengers and eight crew members were killed. Not much more is known about the cause of the crash.

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, on Sun., March 10, 2019. Reuters

While Lion Air Flight 610 and Ethiopian Airlines Flight 302 were both Boeing 737 Max 8s, thus far the only known similarity between the two crashes is that both plummeted shortly after takeoff. The similarities may only be a coincidence.

Boeing said Sunday it is prepared to provide technical assistance at the request of the US National Transportation Safety Board. The Federal Aviation Administration will be conducting an investigation into the cause of the crash as well.

What is the FAA saying?

On Monday afternoon, the FAA sent a "Continued Airworthiness Notification to the International Community," to 59 operators of the 737 Max 8 worldwide. CBS News obtained a copy of the document, which reiterates the FAA's position that its too early to tell what occurred in this crash.

"The FAA continuously assesses and oversees the safety performance of U.S. commercial aircraft," the FAA said in a statement released Monday afternoon. "If we identify an issue that affects safety, the FAA will take immediate and appropriate action."

Later Monday, however, Boeing said the FAA had told the company that it would be ordered to institute safety-related software enhancements to its 737 Max 8 planes by next month. Boeing's statement didn't mention the crash in Ethiopia. It said the changes had been in the works since the Lion Air crash in October.

Boeing said the improvements would be deployed across the entire Max 8 fleet in coming weeks, adding that they're "designed to make an already safe aircraft even safer."

What has Boeing said about the safety of the Max 8?

On Sunday, Boeing said it was sending a technical team to Ethiopia to assist in the investigation, and offered condolences to those killed in the crash.

In a statement Monday, Boeing said the team was working with investigators.

"Safety is our number one priority and we are taking every measure to fully understand all aspects of this accident, working closely with the investigating team and all regulatory authorities involved," the airline said. "The investigation is in its early stages, but at this point, based on the information available, we do not have any basis to issue new guidance to operators."

After the Lion Air crash in October, Boeing and the FAA issued a bulletin to 737 Max 8 and 9 operators warning the anti-stall sensor could produce "erroneous indications" causing the plane's nose to dive. The directive said if the anti-stall sensor is triggered then the plane could face potential nose-dives, cause pilots to have "difficulty controlling the plane" and lead to "possible impact with terrain."

But Boeing has insisted that existing protocols are sufficient for dealing with MCAS malfunctions. Despite that assurance, the company has been working on the software update to the Max, which it now will be forced to implement by FAA order, to address lessons learned from the Lion Air crash.

The U.S. aerospace giant said, meanwhile, that it would delay the ceremonial debut of its brand new 777X plane, which had been scheduled for Wednesday in Seattle, to focus on "supporting" Ethiopian Airlines in the wake of the weekend crash.

"We will look for an opportunity to mark the new plane with the world in the near future," Boeing said in a statement, according to Reuters.

What are other airlines and passengers saying?

CBS News has obtained an internal memo American Airlines sent its employees that suggests the airline is standing by the Boeing 737 Max 8. "American will never operate an unsafe aircraft," the memo said. "Our team regularly monitors aircraft performance and safety parameters across our entire fleet, including extensive flight data collection. This data, along with our analysis, gives us confidence in the safe operation of all of our aircraft, including the 737 MAX 8, and contributes to American's exemplary safety record."

Southwest Airlines said it does not plan to change its operational policies or procedures. "We remain confident in the safety and airworthiness of our fleet of more than 750 Boeing aircraft," the company said in a statement.

On Monday, FlyersRights.org, a non-profit promoting airline passenger rights, called on the FAA to ground the Boeing 737 Max 8 Aircraft. In a statement, the group's president said, "The FAA's 'wait and see' attitude risks lives as well as the safety reputation of the US aviation industry. Even assuming this design defect should not by itself take the aircraft out of service, the failure to warn airlines and pilots of the new feature, and the inadequacy of training requirements, necessitate an immediate temporary grounding of the Boeing 737 MAX 8."