First, have you actually had your BP taken on flights? You suggest that you are nervous. Discuss this with your physician and low dose anti-anxiety medication may be in-order. Perhaps try non-medication approaches such as bio-feedback or other relaxation methods. You and your physician should assure you do not have underlying hypertension or other medical issues that may be contributing to this situation.

Anxiety increases blood pressure. Trying to be calm by practicing breathing exercises or yoga can be helpful.