why these sentenses use past tense ?

above all , let me enumerate some of sentenses considered as strange by me use past tense .
i am concerned about what you guy are going to answer about my question ? (hehe)
I am prepared to have lunch . (there are minutes away ,:-))
they are schedules to take off tomrrow .

all of the sentenses are smooth , but  why these sentense above use use past tense , knowing that all of the subjects can do thing on their initiative ?

i hope my questions won't stump you .
Thank you so much .