The Boeing 737 Max received Federal Aviation Administration approval to reenter commercial service Wednesday morning -- marking an end to one of the longest aircraft groundings in history.
It's been 20 months since U.S. regulators were forced to ground the plane following two crashes that killed 346 people.
In October 2018, Lion Air Flight 610 was airborne for only 13 minutes before it plunged into the Java Sea off the coast of Indonesia. Less than five months later, Ethiopian Airlines Flight 302 crashed near Addis Ababa airport just six minutes after takeoff, killing all on board.
An automated flight control system misfired in both crashes, leaving pilots struggling to regain control and altitude of the plane. That system was not mentioned in the pilot manual.
Boeing decided to rewrite not just the system, but the entire flight computer software. Boeing CEO Dave Calhoun has said he believes the Max is "safer than the safest airplane flying today."
Arguably the biggest challenge will be winning the public's trust after allegations surfaced concerning putting profit over safety, a broken regulation process and a culture of concealment.
In September, House investigators released a scathing report that concluded technical design flaws, faulty assumptions about pilot responses and management failures by both Boeing and the FAA led to the collisions.
"This plane will recover with the flying public when airplane pilots step on it, fly it, like it and by the way, based on all the test flights we have had to date, which are many, they do," Calhoun said in January. "So as all of those pilots return, so will passengers."
American Airlines pilot Capt. Dennis Tajer has been flying commercial planes for more than 30 years.
"I'm not walking down that jet bridge, and nor is any other pilot until we've been assured that this airplane will be fixed, it is fully vetted, it is transparent and we are robustly trained," Tajer, who is also a spokesperson for the Allied Pilots Association, told ABC News Tuesday. "We have yet to see the full training on it."
Although it is ungrounded, the soonest the Max can fly with paying passengers is in December. Airlines are now tasked with training their pilots -- a process that could take months. American Airlines is the only U.S. airline that has said it will resume Max flights in 2020.
Unions representing pilots, flight attendants and mechanics have expressed their support for bipartisan legislation that would strengthen the oversight of the certification process.
On Tuesday, the Aircraft Certification Reform and Accountability Act passed in the House. It will be considered by the Senate on Wednesday.
"Everything in there is geared towards ensuring this never happens again," Tajer said.
But for the family members who lost loved ones in the crashes, the ungrounding is just another painful reminder of what they can't change.
"I miss my daughter," Michael Stumo, who lost his daughter Samya in the crash in Ethiopia, said. "She would be 26 today and we'd be ready to have Thanksgiving next week and we won't."