The Federal Aviation Administration’s decision Wednesday to release the Boeing 737 Max from a 20-month grounding order likely means passengers on at least one airline will begin flying on the planes before year’s end.

Within hours of the FAA’s announcement, American Airlines Chief Operating Officer David Seymour said the airline plans to begin noncommercial Max flights in early December, resuming scheduled service on the Max on Dec. 29 with two flights a day between Miami and LaGuardia Airport in New York City through Jan. 4.

The airline expects to gradually phase more 737 Max aircraft into service throughout January, with up to 36 departures from its Miami hub.

Southwest Airlines CEO Gary Kelly, meanwhile, said the carrier will conduct multiple readiness flights on each of its 34 Max aircraft, completing “thousands of hours of work, inspections, and the software updates before any of our Customers board a Southwest 737 Max.” He did not specify a date when the aircraft would return but estimated it “will likely take place no sooner than the second quarter of 2021.”

[FAA allows 737 Max flights as Hill takes up oversight bills]

United, meanwhile, said it does not expect to return its fleet to service until the first quarter of next year, after completing more than 1,000 hours of work on every aircraft, including FAA-mandated changes to the flight software, additional pilot training, multiple test flights and “meticulous” technical analysis to ensure the planes are ready to fly. Delta does not currently have the Max in its fleet.

The Boeing 737 Max, once a prized update to current 737 aircraft, saw its reputation shattered in the wake of two accidents in 2018 and 2019 that killed 346 people. The aftermath spurred multiple investigations, with the House passing a bill Tuesday tightening FAA oversight of the aircraft certification process.

Senate bill

On Wednesday, the Senate Commerce, Science and Transportation Committee advanced a similar bill.

The Senate bill, said Commerce ranking Democrat Maria Cantwell, D-Wash., “basically is saying that we are requiring of both the FAA and manufacturers more safety assessments and more oversight, that cutting corners is not an option but listening to front-line engineers is the most important aspect of getting this right.”

Cantwell said she conferred with FAA Administrator Steve Dickson about the decision to rescind the grounding order, but she added that “whatever actions are taken today does not alleviate our responsibility for making changes to this process and ensuring that we are going to meet the highest standards of safety possible when it comes to aviation.”

Sens. Richard Blumenthal, D-Conn., and Edward J. Markey, D-Mass., members of the Senate Committee on Commerce, Science and Transportation and frequent critics of the airlines, called the decision to allow the planes to fly “a premature leap of faith.”

“The FAA’s directive to unground 737 MAX aircraft fails to address the larger systemic issues at Boeing and the FAA that led to the deaths of 346 people,” they said. “We have major outstanding concerns about the transparency of the FAA’s risky decision to move forward with the ungrounding.”

Dickson said the 20-month review followed a “methodical and deliberate safety process” that involved the FAA “meticulously” working on fixes to address issues that played a role in the accidents. He cautioned that airlines would have to do maintenance on the 737 Max aircrafts that have been in storage and complete training before they can fly passengers.

“My family and your family will be safe on this aircraft,” he said. “We have not left anything to chance here.”

The review process “reset” the FAA’s relationship with Boeing, which lawmakers criticized as too cozy leading up to certification of the Max, Dickson said.

Boeing President and CEO Dave Calhoun said the approval came after a “comprehensive, robust and transparent certification process” that included “a series of meaningful changes to strengthen the safety practices and culture of our company.” The company strengthened its engineering function, established a product and services safety organization, and implemented an enterprise-wide safety management system in the wake of the crashes.

“We will never forget the 346 victims of the Lion Air Flight 610 and Ethiopian Airlines Flight 302 accidents,” Calhoun said. “We will honor them by holding close the hard lessons learned from this chapter in our history to ensure accidents like these never happen again.”

Lawmakers including Cantwell, Senate Commerce Chairman Roger Wicker, R-Miss., and Rep. Sam Graves, R-Mo., the ranking member of the House Transportation and Infrastructure Committee, praised the work the FAA did to ensure the aircraft’s safety. Graves called the FAA’s efforts leading up to the decision “unprecedented” and “more rigorous than any such review in its history.”

“The bottom line is that the public will not fly if the system isn’t safe, and I have absolute confidence in the FAA’s careful determination that, after incorporating all the necessary updates and improvements, this aircraft is safe for the flying public,” he said.

‘Get this right’

But Rep. Peter A. DeFazio, D-Ore., chairman of the House Committee on Transportation and Infrastructure, was more measured, saying he was grateful that the FAA agreed to Democrats’ request to stand up an independent panel of experts to review Boeing’s proposed changes to the 737 MAX and the FAA’s acceptance of those changes and to assess whether those changes remedy the design errors that resulted in the two deadly crashes.

“It is critical for the FAA to get this right,” he said.

Sara Nelson, international president of the Association of Flight Attendants-CWA, said while the ungrounding is “the result of the persistence of engineers and manufacturing workers at Boeing,” it is “also a reminder of why this plane has not flown for two years and the responsibility we all have to ensure we hear those who questioned or called out what went wrong.”

“The history of the 737 MAX shows what happens when we undermine and starve key government functions,” she said, saying the aircraft was rushed to market without proper review and that regulatory oversight was outsourced to Boeing.

Michael Stumo — father of Samya Rose Stumo, a Massachusetts native who died on Ethiopian Airlines Flight 302 — says he has little faith that the aircraft is safe.

“The flying public should avoid the Max,” Stumo said Tuesday.