When you say "I was about to," you are telling someone that you are going to do something. But maybe another word that prevents you from doing this is "I am about to" but the difference is that you won't do that anymore. Since you won't do that anymore it becomes a past event.
This is why we use "was" instead of "am". Here are examples to help you understand:
- As I was about to leave the postmaster appeared in the doorway.
- But I couldn't do it, since I was about to make Laputa at that time.
- But I couldn't do it, since I was about to make Laputa at that time. -laughs.
- Don't be so nervous?anyone would think I was about to leap on you.
- I dried up just as I was about to talk, even though I had been preparing the speech for weeks.
- I shook with terror whenever I was about to fly in an aeroplane.
- I was about to ask Jack who it was, when the penny dropped.
- I was about to correct him, but I caught myself in time.
- I was about to go home.
- I was about to go out.
- I was about to keep driving by when I saw a man dressed up in an old buckskin jacket and a large worn out hat.
- I was about to learn how to quash hunger.I was about to leave when I noticed someone coming up the driveway.
- I was about to leave when I ran into Mr White.I was about to leave when Mark arrived.I was about to make quietly down the hillside when he moved.I was about to nod off when she knocked the door.I was about to prepare a dessert of mashed potato, flavoured with an Oxo cube.
- I was about to say we should cancel the trip, but she took the words right out of my mouth .
- I was about to say, Harry, that I was accused by some friends last night of being sanctimonious.
- I was about to sink into the quicksand of sin.
- I was about to take a coffee break.
- I was about to take a picture of the penguins when suddenly from the other side of the dune appeared a young elephant seal.
- I was about to take the last cake, but he beat me to it.
- I was about to write you a note and stick it on your windscreen.
- Just as I was about to jump, the driver hit the gas and lurched forward, throwing me off.
- Just as I was about to pick up the pieces of card once more, I stopped transfixed.
- My foot slipped as I was about to shoot and I missed the ball.
- Now I was about to meet him again, it was as if I had suddenly woken up from a syrupy dream.
- Still pinned to the floor I was about to burst into tears of frustration when I was suddenly released.
- The idea was that I should be in the right state of mind for the concert I was about to conduct.
- When I was about to leave with disappointment, I caught sight of a piece of oilcloth among piles of old stuff.
- With an apology for my intrusion, I was about to withdraw.