Here is the answer given by the link Tdol provided for us:
On the fly
If you do things on the fly, you do things without preparation, responding to events as they happen.
I've answered wrong:-( but it's ok i've learned new information thanks.
on the fly: impulsive
on the not: id assume at the request or order
on the trot: consecutive, almost rhythmatic, consistant
On the trot -without break