Boeing 737 Max has been cleared on Wednesday to resume commercial flights in the United States by U.S. safety regulators.

The Federal Aviation Administration (FAA) lifted the grounding orders placed in March 2019 after two fatal crashes that killed everybody on board.

Reports said the fatal crashes had been attributed to the aircraft's faulty MCAS or the Maneuvering Characteristics Augmentation System intended to make it easier to fly. 

Many passengers are still reluctant to board the infamous airlines because of the deadly crashes, reported NBC News. Thus, U.S. airlines noted that they would allow Max passengers to change their tickets for free if they don't feel comfortable flying on the said jet.

"If our pilots, along with the APA (Allied Pilots Association), FAA, and our safety teams are confident the aircraft is safe, we are confident in its return to service," David Seymour, chief operating officer of American Airlines, said in a letter signed by five other top executives for the company, as NBC News reported. 

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The APA is the union representing pilots of American Airlines. Seymour added that if a customer does not want to fly on the 737 Max, they won't have to.

A United Airlines spokesperson earlier said that customers who are booked to fly on a Max aircraft but would like to rebook because they do not want to fly on a Max could do it at no charge.

A Southwest Airlines spokesperson also said that the firm would also accommodate free changes for customers who don't feel comfortable flying the Max.

One passenger, Jenn Cammorato, said she'd change her ticket or make the reservation over the phone to make sure that she's not flying on a Max. Cammorato, a revenue manager for a rental company from Los Angeles, noted that she no longer wants to fly on any Boeing planes anymore.

Other passengers view it differently. Lou Nunzio, a mechanical engineer from Safety Harbor, Florida, said that flying is a commodity and she will fly on whatever cheapest ticket she could get. Nunzio added that flying is still significantly safer than driving, even on a Max plane.

Airlines advised customers to look at their itineraries. In this way, they can see which kind of aircraft they will be flying on.

Brian Kelly, founder and CEO of The Points Guy, told NBC that most airlines now that "have the plane will show it as the Boeing 737 Max 8 or Max 9 at booking." The Points Guy is a travel advice site.

"There's been talk that some airlines could rebrand the Max as a 737-8 or Boeing 737-9 - which is different from the non-Max Boeing 737-800 or 737-900," said Kelly, adding that it is something to look for. 

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The airlines said passengers could request a different flight, and fare changes or ticket fees will be waived.

The airlines added that the customers could also request refunds for refundable tickets. Non-refundable tickets, on the other hand, can be canceled and turned into credits for future flights.

Meanwhile, aircraft changes can happen on the actual day of the travel itself. Thus, there could be a chance that a passenger who opted not to fly on a Max may find that it is the only one available at the moment.

Commercial pilot Marc Himelhoch said bringing a grounded jet back into service will need a long list of maintenance actions, inspections, and operational flight tests.

It will also include training pilots on updated software and emergency procedures approved by the FAA during the Max recertification, he added.

The commercial pilot explained that it would probably take months for all these requirements to be done and get the planes back into revenue service.

On Wednesday, Boeing said it is working closely with airlines to provide recommendations regarding the airplanes' safe return to service.