The weekend crash of a new airliner in Ethiopia had both aviation experts and the public flying wondering on Monday if it is an indication of a larger safety issue with an aircraft designed to be a workhorse of the industry -- the Boeing 737 MAX.
When Ethiopian Airlines Flight 302 crashed just six minutes after takeoff on Sunday, killing all 157 people on board, comparisons were immediately made with an October 2018 crash in Indonesia involving the same type of plane.
So far, it is unclear how much that crash and last fall's Lion Air Flight 610 crash have in common other than the aircraft type and that flights went down shortly after takeoff while apparently struggling to gain altitude.
The Lion Air accident that ended with the plane plummeting into the Java Sea appeared to have been caused by pilot error and poor maintenance, according to experts who reviewed the publicly-released data.
So what is the MAX aircraft? What do we know about its accident record? Is it safe? And when are we going to learn more?
The MAX series is designed to fly more people, further than previous 737s
The Boeing 737 is the best-selling commercial airliner in the history of aviation and the MAX series is its latest iteration, done in a move to make the aircraft serve more people, on longer routes.
Originally developed as a smaller aircraft for shorter routes, it has, over time, been developed to serve a network as large as the United States. The latest version came to life in 2017 with the launch of the 737 MAX 8. (The MAX 9 and MAX 10 are its higher-capacity siblings.)
It has more powerful engines operating with far greater efficiency, allowing a larger number of travelers to fly with less cost to the airline. The new power and increased aerodynamics also allow the aircraft to fly long distances, such as flights from the continental U.S. to Hawaii, with ease.
The two engines on the aircraft protrude forward more than on previous models and sit higher on the wing, affecting the balance of the aircraft.
The new design of the winglets -- at the tips of the wings -- is the most efficient of any airplane, according to Boeing engineers. The reshaping of the wings helps reduce drag.
Boeing also introduced a new flight control safety system on the MAX — called MCAS (Maneuvering Characteristics Augmentation System) — that senses if the aircraft is flying at an improper angle and, if needed, puts the nose down in order to prevent a stall. Experts believe it was a component of this system that was improperly maintained before the 737 MAX 8 crashed in Indonesia in October. It's unknown if this system played a role in Sunday's accident.
The aircraft appeared to struggle to gain altitude upon takeoff
Investigators have more questions than answers about the accident in Ethiopia this weekend. The plane left Addis Ababa that morning and suffered control issues almost immediately, according to data from Flightradar24 and analyzed by ABC News.
The aircraft appeared to start "porpoising," or struggling to maintain a consistent altitude. The pilots requested a return to the airport and available data was lost just 6 minutes after takeoff. The MAX aircraft appears to never have reached an altitude above 1,000 feet.
Debris from the crash was found in a deep crater over a relatively small area outside of Addis Ababa. The compact field of aircraft parts and personal belongings often indicates a steep-angle crash.
Investigators have found the black boxes, the airline says
In a statement released on Monday, Ethiopian Airlines said both the flight data recorder and the cockpit voice recorder were recovered from the crash scene, making up the black boxes and the most critical pieces of evidence.
If in good condition, the black boxes are expected to paint a clearer picture of every moment in the cockpit and the functions of the flight control systems. The cockpit voice recorder records every sound in the cockpit, from the voices of the pilots to any audible alerts they heard.
It's unclear when an analysis of the black boxes will be released. In American investigations, a summary is typically provided weeks after the accident. The Ethiopians are in charge of the investigation but are expected to seek international assistance in the readout of the flight recorders. The National Transportation Safety Board told ABC News on Monday it is prepared to quickly asses the conditions of the boxes and, if the request comes from the African nation, analyze them.
Four NTSB and four FAA investigators were arriving in Addis Ababa Monday, the agencies told ABC News.
U.S. aviation officials are not expected to ground the 737 MAX without more evidence
Federal aviation sources told ABC News the FAA is not expected to ground the Boeing 737 MAX without information that indicates the aircraft is unsafe. The agency tweeted on Monday that it would issue a Continued Airworthiness Notification to the International Community, a reiteration that the aircraft is considered safe and worthy of international service.
"If we identify an issue that affects safety, the FAA will take immediate and appropriate action," the FAA said in a statement on Monday.
American Airlines, Southwest Airlines and United Airlines all fly the Boeing 737 MAX aircraft and say they are confident in its safety. Sources at the airlines told ABC News they have not encountered the "Angle of Attack" issues reported by the Lion Air pilots. An improperly maintained sensor is believed to have caused the incorrect readings in the MCAS system. After that accident, the FAA reissued existing guidance on how pilots should react if the MCAS system is malfunctioning — effectively telling pilots to turn it off and manually fly the airplane.
Southwest Airlines, one of the first to invest in the series, flies the most 737 MAXs of any U.S. carrier with 34 in its fleet flying all over the country. American Airlines has 24 in its fleet, mostly based out of Miami and serving its Caribbean routes. United Airlines operates 14, most of which fly in and out of Houston.