Dear Charlie,
Kindly excuse me for my not being able to see you off at the airport this Saturday as I have promised. A major business partner of our company will be attending an important conference in Xiamen this weekend, and my boss finally chooses me to accompany him there to negotiate about a new transaction. I have just been informed of this plan and am happy about the decision—this is an opportunity to both display and enhance my abilities, so I am afraid I cannot be present at the airport. Pursuing study overseas is an essential step in the accomplishment of your dream.
Sincerely yours,