The first Boeing 737 Max crash happened a year ago today - here's how the saga unfolded, and the ongoing fallout as the plane remains grounded worldwide

This was the first-ever crash of a 737 Max, the newest model of Boeing's storied 737 line. The aircraft type had entered service just one year earlier.

Within days, investigators began to suspect an automated system on the 737 Max called the Maneuvering Characteristics Augmentation System, or MCAS, may have been involved.

MCAS was designed to compensate for the fact that the 737 Max has larger engines than previous 737 generations. The larger engines could cause the plane's nose to tip upward, leading to a stall. In that situation, MCAS could automatically point the nose downward to negate the effect of the engine size.

That meant that from the pilots' perspective, the plane would handle exactly like the previous generations of 737, making it easy for airlines to integrate the new aircraft type into their fleets.

However, it appeared that MCAS had erroneously engaged, forcing the plane's nose downward when it had been flying normally.

On the plane's previous flight, pilots reported incorrect airspeed and altitude readings, as well as similar flight-control problems. However, they were able to land the aircraft successfully. It was not clear why the airline did not remove the plane from service at that point to investigate the issue.

Indonesian investigators noted in their final report, released last week, that 31 pages were missing from the airline's maintenance log for the jet.

Investigations showed that MCAS engaged because it could be activated by a single sensor reading — in both crashes, the sensors are suspected of having failed, sending erroneous data to the flight computer and, without a redundant check in place, triggering the automated system.

MCAS is suspected of playing a similar role in the March 2019 crash of Ethiopian Airlines flight 302.

Boeing initially excluded mentions of MCAS from the pilot's manual, arguing to the FAA that, since it was designed to work in the background, and should activate only under very rare conditions, full understanding of it wasn't crucial for pilots operating the plane.

The ensuing investigations of the crash have faulted Boeing for failing to adequately explain the MCAS system, making it vulnerable to bad data from a single failed sensor, as well as for failing to build a fail-safe to deactivate it.

The airline has also been faulted for failing to remove the plane from service, while the pilots have been criticized for responding poorly to a series of alerts in the cockpit, and for failing to follow an emergency checklist that could have saved the plane — one which pilots on the previous flight had followed.

After the crash, Indonesia's Transportation Ministry ordered emergency inspections on all of the 737 Max 8s within the country — all were determined to be airworthy within two days.

Although there was discussion of grounding the 737 Max following the Lion Air crash, Boeing and the FAA assured airlines and global regulators that the plane was safe.

On November 6, the FAA and Boeing said that they planned to issue an Airworthiness Directive warning about possible trim stabilizer control issues due to faulty angle-of-attack indicators. Boeing began working on a software fix to prevent MCAS from inadvertently activating, and disseminated the procedure to deactivate the software in an emergency.

On the morning of March 10, 2019, Ethiopian Airlines flight 302 took off from Addis Ababa. Pilots reported flight-control problems within a minute of leaving the runway. They disabled the electrical trim tab system, but were unable to manually turn the wheel that would change the trim by hand, partly because they had inadvertently left the engines on full thrust from takeoff.

After six minutes, it slammed into the ground, killing all 146 aboard. MCAS was again cited as a contributing cause, combined with the fact that pilots could not adjust the stabilizer trim by hand.

The same day of the crash, Ethiopian Airlines grounded the rest of its 737 Max aircraft. A day later, the Chinese aviation authority — the Civil Aviation Administration of China, or CAAC — ordered the country's airlines to stop flying the plane.

Regulators around the world followed, parking their 737 Max planes on March 11 and 12. The FAA was a lone holdout, initially insisting that the plane was airworthy. However, the agency followed its international counterparts and ordered the plane grounded on March 13.

The planes have remained grounded since, as Boeing has worked to complete a software redesign and improve recovery procedures from errant flight system activations.

After the second crash, Boeing said that it was working on a software fix, which it expected to distribute within a few weeks. The FAA had said it expected the software to be approved by the end of March, but it announced a delay in early April, saying that it anticipated receiving "Boeing's final package of its software enhancement over the coming weeks for FAA approval."

However, that delay stretched on as Boeing and the FAA continued to scrutinize the plane. Eventually, Boeing CEO Dennis Muilenburg said during a July conference call with investors and analysts that the plane maker expected to submit the final fix to the FAA in September and fly the necessary certification flights, with approval coming in the fourth quarter of 2019.

It is not clear whether Boeing met its self-imposed September submission deadline, although it has maintained that it expects the plane to be recertified — at least in the US — by the end of the fourth quarter.

US airlines have all pulled the jet from their schedules until at least early 2020. Even if the plane is recertified in 2019, it will likely take airlines longer to install the software and prepare stored planes to fly again.

The FAA said that it would "follow a thorough process, not a prescribed timeline, for returning the aircraft to passenger service."

Boeing is a globally respected legacy plane maker, the largest American exporter, and an all-around corporate America success story. The FAA is a governing body that has been at the forefront of global aviation safety and regulation. Both entities have seen their reputations severely tarnished by the ongoing scandal surrounding the 737 Max.

Boeing has been accused of rushing to complete the 737 Max without due regard for safety, and for fostering a high-pressure culture that leaves engineers scrambling to complete impractical, heavy workloads by corporate due dates.

This manifested in the 737 Max's development in a variety of ways, including a hurried design stage, a failure to catch and fix obvious safety issues — such as making it so that MCAS could be activated by a single broken sensor, without any redundancies — and an allegedly negligent push to downplay MCAS to the FAA in order to get the plane certified as an updated model of the older 737, rather than a new plane with substantial changes.

Evidence suggests that Boeing employees knew there were problems with MCAS, but did not raise them with regulators.

Boeing CEO Dennis Muilenburg has been stripped of his additional title as chairman of the board, and there have been calls for him to be removed as CEO as well. The head of Boeing's commercial airplane division has also been replaced.

The FAA, similarly, has been criticized for failing to properly supervise Boeing's development of the plane, and inadequately scrutinizing it during the certification process.

One aspect of this is the fact that the FAA allows Boeing to self-certify certain technical aspects of its planes.

While this is common practice, it is only effective when there is "adequate FAA engagement and oversight," according to a report from an international panel of air safety regulatory experts. "However, in the B737 Max program, the FAA had inadequate awareness of the MCAS function which, coupled with limited involvement, resulted in an inability of the FAA to provide an independent assessment of the adequacy of the Boeing-proposed certification activities associated with MCAS."

Recent reports have suggested that global regulators may not be willing to rely on the FAA's findings when it reevaluates the plane after Boeing submits its fix.

Typically when a new plane — or a change to an existing plane — is certified, the aviation regulator from the plane maker's country of origin takes the lead on reviewing it and approving it for service, and other global regulators follow suit after a cursory review based on the original agency's findings.

The reciprocal process saves time for all involved, including the plane-maker and airline customers, since the baseline standards that the regulators adhere to are generally accepted. The plane manufacturers, who are aware of the requirements, design the aircraft from the ground up to meet those requirements and avoid costly delays.

However, European regulators have said they want to conduct their own test flights of the fixed Max, and may want to carry out a closer inspection as well. Other regulators, including those from China, have expressed similar sentiments.

"With the 737 Max we are a bit worried ... because we don't see the normal unanimity among international regulators that should be the case," Alexandre de Juniac, director general of the International Air Transport Association (IATA), told reporters last month. "We see a discrepancy that's detrimental to the industry."

As investigations into the causes of the two crashes wrap up, there are still several questions remaining.

One of the biggest is whether there was criminal negligence in the design of the plane. Did Boeing deliberately hide the fatal flaws? Were the outcomes — two fatal crashes — predictable and avoidable? Should Boeing and the FAA have supported grounding the plane type after the Lion Air crash?

There are numerous lawsuits and investigations pending, and answers will likely emerge from them.

When the plane will return to service is another question without a clear answer. Airlines are eager for the plane to return, as each grounded and undelivered plane is lost capacity throughout its routes. They are also eager for compensation from Boeing, given hundreds of millions of dollars of lost revenue attributable to the grounding.

Although Boeing maintains that it expects the plane to be recertified sometime this quarter, there is little certainty surrounding its return. There is also the question of whether the world's regulators will respect the FAA's findings, or conduct their own inspections.

Similarly, there are questions on what this will mean for future new and updated aircraft, such as Boeing's upcoming 777X next-generation plane.

About a year after the Max was initially certified, legislation — lobbied for by Boeing — passed granting additional self-certification privileges to plane makers, and diminishing the FAA's regulatory authority. The legal changes, and Boeing's lobbying role, were recently reported by The New York Times.

Given the scrutiny over the Max, will this law be amended? And if not, how will it be carried out in practice when it comes time to make sure that something like the Max situation is prevented in the future?

Although it has been a year since the crash, the saga is still unfolding, and more will likely develop in coming months and even years.

But today, Boeing, the FAA, and the world's airlines continue to work to get the plane back into the air — safely.