Only the expenses that are incurred wholly & exclusively for the purpose of carrying on the business of the company are allowed to be expended by the director. The director of the company has to incur the personal expenses from teh remuneration paid by the company to the director.
However as stated by you if the airline expenses is related to teh business of the company then that can be shown as an legitimate expense of teh bsuiness. However other personal expenses incurred by teh company on behalf of the director such as medical expenses, rent free accomodation, provision of car etc... can be considered as legitimate busniess expense.