The purpose of this question is for the interviewer to see that you have the confidence needed to succeed in Boeing's high-expectations, challenging environment. If you are great under pressure, you are likely the type of person who can jump into a leadership role, without much notice, and still succeed.
Think about a time when, as a leader, you worked under pressure, without succumbing to stress, and delivering a positive outcome. Outline for the interviewer how you made it all happen. Perhaps you used your excellent time management and communication skills. It's also important to highlight the situations' most significant win.
Remember: Boeing uses behavioral-based questions to conduct interviews, and they advise using the STAR (Situation, Task, Action, and Result) method when responding. Be sure your answer is highly specific and includes quantifiable details and tangible results.