yeah atleast a year
thats why i said a year or more

but for every plane, they still can find problems
nothing is perfect

when testing, they mainly find out major bugs and problems and solve them, whatever they find, they solve

when something breaks, its the technicians that work in the airlines that fixes the planes
so its the responsibilities of the airlines to maintain and fix problems
i have a friend who does maintenance for China Airline (in Taiwan, nothing to do with mainland China)

when something breaks and an accident occurs or keep on occuring on the same model, usually airlines buys other models with less incidents so Boeing or Airbus makes less money
since MD was out of the scheme, its been a battle of safety for Boeing and Airbus