FAA has authorized Boeing Max 9 planes for takeoff once again, after grounded them for several weeks.

But passengers still have concerns about their safety after the planes were grounded for safety reasons include a door “plug” coming off one during a flight.

Passengers can tell when booking which planes they will be on when booking.

United Airlines and Alaska Airlines, the only two airlines that use such models, are offering flexible cancellation policies for passengers who are not comfortable flying on the Max 9 model. Any such passenger may choose to transfer onto a different flight at no extra cost.

Boeing says the Max 9 planes are entirely safe following a rigorous inspection process, and each plane has been certified to airworthy standards by the FAA.