Dear sir,
Concerning this question
-Because of the bad weather conditions, British Airways regrets……..its flight to Cairo.
a) to cancel
b) cancelling
I think b (cancelling)is ok here.
It means the action is done.
If we choose “to cancel” it refers to something that it hasn’t been done yet, but we feel regret in our mind to do it.If we say “to cancel” the passengers may think the flight cancellation is still under discussion.I think gerund means; 1-cancelling 2-regretting.