Craig Mitchelldyer/APAfter weeks of taking the Boeing Max 9s out of commission, the FAA is clearing the planes for takeoff. The experience is making some flyers think twice about flying on Boeing 737 Max 9 planes. While passengers safely returned to the Portland International Airport, the Federal Aviation Administration grounded all 737 Max 9 planes. United Airlines and Alaska Airlines are the only US airlines flying Boeing 737 Max 9 planes. Elizabeth Le/APAlthough United and Alaska Airlines offer flexible cancellation for passengers flying Boeing 737 Max 9 planes, the Max 9s are not the only Max model that has had problems.