For the second time in less than six months, a brand-new Boeing aircraft has crashed just minutes into a flight.
All 157 people on board the Ethiopian Airlines flight from Addis Ababa that crashed on Sunday morning have died, the airline has confirmed.
The tragedy follows the Lion Air flight that went down over the Java Sea in late October, killing all 189 people on board.
There is no suggestion yet as to what caused the latest disaster, and no evidence that the two incidents are linked in causality.
What is known, however, is that both flights took place on the Boeing 737 MAX 8 -- a new model recently unveiled to great fanfare by the US aviation giant, that saw its first flight less than two years ago.
"It's highly suspicious," said Mary Schiavo, a CNN aviation analyst and the former Inspector General of the U.S. Transportation Department. "Here we have a brand-new aircraft that's gone down twice in a year. That rings alarm bells in the aviation industry, because that just doesn't happen."
Adding to concerns are some similarities between the two flights. Both were operated by well-known airlines with strong safety records -- but the Lion Air flight went down 13 minutes after take off, while Sunday's Ethiopian Airlines flight crashed just six minutes into its journey.
And while the Ethiopian Airlines did not see the wild fluctuations in altitude that the Lion Air flight saw, it did dip and then regain altitude before it crashed.
"The similarities with Lion Air are too great not to be concerned," Schiavo said.
Data from flight recorders awaited
At the root of October's Lion Air crash was a new safety system installed in the MAX 8 plane, known as the Maneuvering Characteristics Augmentation System (MCAS), that automatically pulls the plane's nose down if data suggests it is at risk.
In that flight, the system was responding to faulty data that suggested the nose was tilted at a higher angle than it was, indicating the plane was at risk of stalling.
The pilots subsequently engaged in a futile tug-of-war with the plane's automatic systems, trying to reverse a nosedive that should not be triggered so soon after takeoff. Boeing has argued that pilots should have identified the system was in operation, and turned it off.
"All pilots should have been trained on that function after Lion Air," Schiavo added. "Boeing did something very unusual for any manufacturer -- it sent out an emergency bulletin and told all airlines to make sure they trained the pilots in the shut-off procedure."
"This is one of the things that should never be happening after takeoff," Schiavo said.
It is too early for conclusions to be drawn as to whether the same issue occurred on the Ethiopian Airlines flight -- but a clue could come sooner rather than later.
"We will not get a final determination for two or three years, but we will get information from the flight recorders -- which I'm guessing will be fairly easy to retrieve -- in a matter of weeks," said CNN anchor Richard Quest, who specializes in aviation.
"At the moment, it seems a coincidence" that both disasters occurred on the same aircraft, Quest said. "But I'm guaranteeing to you that the authorities will be examining just how close a coincidence, and whether there are common circumstances between the two," he said.
"Two brand new planes have crashed from two respected airlines," Quest added. "Ethiopian is a very, very well-run airline. There is no safety issue on Ethiopian Airlines."
Possible repercussions for Boeing
If investigators do uncover a similar cause of the two accidents, the repercussions for Boeing could be dramatic.
"The Lion Air flight was a big deal for Boeing, but they managed to overcome it," Schiavo says. "They put out the emergency warning about training, and the industry went on. With the second one, I don't think everybody's going to forget."
The MAX 8 could be grounded if a link is found -- either by the company itself, or by governments, though the former is more likely to come first, Schiavo says. "The voluntary basis is always the better way to go -- but it will be expensive for Boeing."
Airlines with MAX 8 aircraft in their fleet -- and those with outstanding MAX 8 orders -- are likely to be watching developments closely in the coming days and weeks.
According to Boeing's most recent reports , 350 MAX planes have already been delivered to airlines across the world. A further 4,661 have been ordered.
The plane that crashed on Sunday morning was delivered to Ethiopian Airlines in November. It was one of five active MAX 8 aircraft belonging to the airline, and another was on order, according to the website PlaneSpotters, which tracks aircraft orders.
'The workhorse of the world'
The highly anticipated 737 MAX 8 was the first member of the company's new series of more efficient, single-aisle plane family.
The planes, which also include MAX 7, 9 and 10 models, were intended to compete with Airbus A320neo family aircraft in an ongoing battle to dominate the global narrow-body market segment.
Together, they mark the latest versions of a jet that was first introduced in 1967. More than 10,000 737s have been produced, making it the best-selling jetliner of all time.
"It's an outstanding aeroplane," Jeffrey Thomas, editor-in-chief of Airline Ratings, told CNN. "The 737 is the most widely used aeroplane in the world -- there's over 7,000 of them flying at the moment... it's the workhorse of the world."
"It has an extraordinary record over the decades. An amazing safety records," he added, referring to the wider 737 model.
But the new MAX 8 models have previously been placed under scrutiny.
In 2017, Boeing temporarily grounded all 737 MAX planes over concerns about a manufacturing quality issue inside its new engines.
Jamie Jewell, a spokesperson for the plane's engine maker CFM International, said at the time that the company's inspections found "some anomalies in the process" of manufacturing disks for the jet's turbine. Jewell also stressed that no problems related to the part were seen in the more than 2,000 hours of test flights for the 737 Max.
"Out of an abundance of caution, we decided to temporarily suspend MAX flights. The step is consistent with our priority focus on safety for all who use and fly our products," the plane maker said in a 2017 statement.
The MAX versions of the 737s are touted for their LEAP jet engines which Boeing says "redefine the future of efficient and environmentally friendly air travel." Boeing says the 737 MAX jets are 10% to 12% more efficient that their predecessors.
Until an investigation is launched, it is difficult to determine whether the Ethiopian Airlines disaster was the result of a failure in the aircraft, human error, or another factor.
Boeing did provide CNN with comment regarding the MAX 8 model, but have released a statement saying it is "deeply saddened to learn of the passing of the passengers and crew." It added that a "Boeing technical team is prepared to provide technical assistance at the request and under the direction of the U.S. National Transportation Safety Board."