The pilot and co-pilot of the 737 MAX 8 were more than experienced, with around 11,000 flying hours between them.
The weather conditions were not an issue and the flight was routine.
So what caused that plane to crash into the Java Sea just 13 minutes after takeoff?
More than two weeks after the catastrophe, investigators are still piecing together the clues.
A lawsuit against Boeing related to the crash was filed Thursday. The parents of one passenger sued the company, claiming that the downed plane, a 737 MAX 8, had an unsafe design. The suit alleges Boeing failed to communicate a new safety feature that had not existed in previous 737s.
Lion Air's operational director has accused Boeing of withholding information from pilots in the manuals about a safety feature that automatically lowers the airplane's nose to prevent or exit a stall.
Boeing Chief Executive Dennis Muilenburg told Fox Business Network on Tuesday that information was available as part of the training manual.
On Wednesday, a Boeing spokesperson said in an email that the company could not "discuss specifics of an ongoing investigation" and that the company had "provided two updates for our operators around the world that re-emphasize existing procedures for these situations."
"We are confident in the safety of the 737 MAX. Safety remains our top priority and is a core value for everyone at Boeing," the spokesperson said.
CNN has spoken to nine aviation experts, including pilots who fly the 737 MAX 8 plans, about the crash. While they all emphasized that only a complete investigation will give a full picture of what actually happened in the cockpit that morning, all have concluded that, in one way or another, Boeing's actions fell short – leaving not only the families of the victims shaken , but also the aviation industry.
Boeing declined to comment for this article, referring CNN to its most recent statement cited above.
In recent years, Lion Air, the popular Indonesian budget carrier, had given itself a makeover.
In 2011, Lion Air announced a $ 21.7 billion order for 230 of the single-aisle, twin-engine jets – the largest single order for commercial jets in its history at the time, according to Boeing.
Those upgrades may have signed a bid by Lion Air to rectify its spotty safety record over the last decade, including a 2013 non-fatal crash and a ban from European and US airspace between 2007 and 2016.
The European and US bans have since been lifted, with the international civil aviation organization giving the airline its top rating in terms of safety this year. The MAX 8s have been a visible part of that boost.
But with any new fleet, pilots must undergo additional training.
"Generally speaking, when there is a new delivery of aircraft – even though they are the same family – airline operators are required to send their pilots for training," Bijan Vasigh, Professor of Economics and Finance at Embry-Riddle Aeronautical University, told CNN.
Those training sessions generally take only a few days, but they give the pilots time to familiarize themselves with any new features or changes to the system, Vasigh said.
One of the Max 8's new features is an anti-stalling device, the maneuvering characteristics augmentation system (MCAS). If the MCAS detects that the plane is flying too slowly or steeply, and at risk of stalling, it can automatically lower the airplane's nose.
It's meant to be a safety mechanism. But the problem, according to Lion Air and a growing chorus of international pilots, was that no one knew about that system.
Zwingli Silalahi, Lion Air's operational director, said that Boeing did not suggest additional training for pilots operating the 737 MAX 8. "We did not receive any information from Boeing or from regulator about that additional training for our pilots," Zwingli told CNN Wednesday .
"We do not have that in the manual of the Boeing 737 MAX 8. That's why we do not have the special training for that specific situation," he said.
Investigators are currently examining whether the angle of attack (AOA) sensor on the outside of the Lion Air plane issued incorrect data that could have triggered the MCAS to force the plane's naose down.
An AOA sensor is an instrument, similar to a small wind vane, that sits outside the plane just below the cockpit and sends information to its computers about the angle of the plane's nose relative to the oncoming air. The sensor helps to determine whether the plane is about to stall and dive.
Investigators said that the day before the crash, the jet experienced problems with its AOA sensor, which was replaced. The last four flights – including, crucially, the flight that crashed, according to Soerjanto Tjahjono, the head of Indonesia's National Transportation Safety Committee (KNKT) also had problems.
CNN has asked Boeing for a copy of the original manuals issued to carriers who bought the Boeing 737 MAX 8. Boeing has not provided those operating manuals to CNN. Representatives from American, United and Southwest airlines have all told CNN that Boeing did not include information in its Flight Crew Operations Manual that explained the functions of the new feature.
CNN has reviewed updated guidance issued by Boeing on November 6, and a subsequent Federal Aviation Administration (FAA) emergency directive that reinforced Boeing's update on November 7.
Mary Schiavo, a CNN aviation analyst and the former Inspector General of the United States Department of Transportation, said that one of the selling points of the Boeing 737 fleet is that pilots can move from one plane to another easily if they are already trained on one of the jets.
The fact that Boeing could have failed to include the proper guidance on the new manual could have been an oversight, she said. She also said that updating a manual can be a long process for manufacturers and airlines.
It's possible that Boeing could have downplayed the changes to the system as a selling point, according to Schiavo, who added that she hoped the error was an "innocent" one.
Boeing likely "assumed it would save the plane when it looks like it might have doomed the plane," she added.
A Federal Aviation Authority (FAA) emergency directive sent to all MAX 8 operators on November 7 explained that pilots can stop a malfunctioning automated system on those plans by pressing two buttons.
The FAA bulletin said that all carriers were to revise their manuals within three days. "This condition, if not addressed, could cause the flight crew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain," it said.
Automated systems are known to occasionally malfunction, but trained pilots will know how to counteract those systems. Not sharing that information, Schiavo said, is another matter.
If pilots were unaware of a new feature – or how to shut it off if it malfunctions – they would be set up for failure, she said.
"All these improvements they (Boeing) market as more efficient and safe. To do that without the training on how to turn it off … I think that the investigators and the reports … will find it was not an excusable mistake, "she said, referencing another flight, the 2003 Colgan Air 9446 crash, where the aircraft also experienced a full trim nose down, and was unable to recover.
There's no way of being able to physically overcome the strength it takes to counteract a full nose stop down, she said, estimating the weight at around 800 pounds of force in the 2003 Colgan Air crash, noting that it was a much smaller regional plane where the pilots were not fighting a computer.
"I think the industry, the pilot's union – everyone is so stunned that the plane could do this and that the pilots were not trained to turn it off knowing it could be a fatal dive," Schiavo said.
Richard Aboulafia, vice president of analysis at the aerospace and defense consulting company, Teal Group Corporation, told CNN that he could not imagine that Boeing would intentionally leave out important information to pilots just to get a competitive edge over its industry rival.
"I really can not imagine that being the case, because the system does not really require a lot of extra training – frankly (adding) just an extra page in the book would have sufficed. So, the idea that they did it for competitive reasons, I just do not get that, "Aboulafia said.
Instead, he believes that it's possible that it might have been an oversight or a "technical error."
Aboulafia says that it's "encouraging" that pilots are voicing their concerns as their feedback helps keep the industry safe.
"If I were a consumer I would feel happy that the pilots were making their voices heard. And happy that there was cooperation between manufacturers and regulatory authorities and between the airlines and the pilots – it's exactly that process that's made the system what it is Over the past century of aviation. It's a very healthy triangle of people who communicate and you are seeing that unfold right now as we speak. "
Unaware of safety features
Dennis Tajer is one of those pilots who has flown the 737 MAX 8 plans. The veteran 737 captain for American Airlines, who is a spokesperson for its 15,000 member pilot union, the Allied Pilots Association (APA), told CNN the first time he learned about the MCAS safety feature was through a bulletin issued by Boeing on November 6.
The company said the bulletin was meant to reinforce procedures already in the 737 MAX flight manual. The APA rejects that claim. Tajer said Boeing broke his trust, the key component of a safety culture that he has been an active part of for over 10 years.
"When you are describing components of the aircraft that we had no idea that existed, that's what's troubling," Tajer said of his first read of that bulletin.
"We want to know about the new system – and you are using the cloak of the stabilizer checklist (another related system) to describe things to which I had no knowledge existed," he said.
Tajer imagines what it might have been like for the Lion Air pilots, who he believes, were also unaware of the new system and would have been struggling to understand what was going in the cockpit.
"They are human beings that are trying to process just what the heck was going on. Like a crowd of 10 people yelling at them while a nefarious and insidious system they had no idea was running on the airplane, is actually running against you."
But not all pilots are pointing the finger at Boeing.
Capt. Todd Insler, ALPA's chairman of the United branch, said that Lion Air pilots should have been aware of that procedure and that it was too soon to say anything more about the cause of the Lion Air crash.
"The story here is not why we did not know about (the new system), it's why the pilots did not fly the plane," Insler said.
In a letter sent by the ALPA President Capt. Tim Canoll to the FAA and the US National Transportation Safety Board on Thursday, the ALPA said they were "concerned that a potential, significant aviation system safety deficiency exists" and asked for "immediate help and assistance in clarifying the issues with respect to the pitch control system of the aircraft. "
It added: "More importantly … reports indicate that information regarding the normal and non-normal operation of this system was not provided to the frontline airline employees – the flight crews and maintenance technicians."
Veteran pilot and author Patrick Smith, who does not fly 737 MAX planes, told CNN that it's too soon to determine what could have gone wrong, but that it's possible to say that an alleged system malfunction is not entirely to blame.
Both Smith and Tajer believe though, that as dark and horrific as the Lion Air crash was, it has compelled the industry to face difficult questions and push for more transparency and positive learning outcomes, with passengers' safety at the helm.
Tajer says that now, his trust in the company is slowly rebuilding and that MAX 8 pilots are not flying with hesitation now because they have broken through the "sound barrier" of information.
"We will not fly an airplane that's not safe, we've got our customers' backs."
Aboulafia agrees that there is no reason for consumers to be concerned about what could be a freak incident, adding that technological advances in the industry over the last century have demonstrated that flying is "now the safest form of transpiration ever been designed in the history of mankind. "
"We do not know the full details of this crash yet, but as for other systems have never been safer," Aboulafia said.
Schiavo is a bit more cautious.
"I personally would avoid the 737 MAX until there is time for the pilots to be retrained," she said. "I like my pilots to know how to troubleshoot in the air."
Boeing, which made no comment on the allegations, said it was "deeply saddened by the loss of Lion Air Flight JT 610."
"We extend our heartfelt condolences and sympathies to the families and loved ones of those on board."
Automation as collaboration
The Lion Air crash has again reignited a larger conversation about the use of automated control systems and whether cockpit procedures surrounding these systems are as safe as they should be.
It's the latest fatal crash involving an auto flight control system. Both the Air France 447, and AirAsia Flight 8501 crashes had flight-control systems and pilots working against each other with disastrous outcomes, begging the question of whether these systems help or hinder pilots.
Peter Goetz, a CNN aviation analyst and former managing director of the National Transportation Safety Board, believes ultimately, the onus is on transparency and training, and not on automation.
"Pilots are extraordinarily skilled and if they have the right training and information they will make the right decisions, they will do the right thing. But if they do not know what's confronting them and there's been an increasing reliance on the infallibility of fly- by-wire systems, then you are faced with a real challenge. That's a broader question that's going to be looked at. "
Tajer agrees. He says that technology has definitely increased the safety of our global flight systems but just like a singular dietary plan, it's not always healthy.
"Automation is an outstanding addition to the aircraft when it's in collaboration," Tajer said.
"But when you do not tell the human about it, it disconnects the human being from the system."