On the flight deck, the startle effect is triggered by sudden, unexpected and possibly threatening events such as bird strikes or system failures. It is a very rapid protective and defensive reaction that can lead to a partial or total incapacitation of pilots with tragic consequences. With Single Pilot and Reduced Crew operations likely being implemented in the future, the single pilot will be forced to face and handle the startle effect alone in the cockpit. We designed and developed FOCUS (Flight Operational Companion for Unexpected Situations), an intelligent assistant designed to help single pilots overcome the startle effect. FOCUS supports pilots in regulating their stress and maintaining an adequate situational awareness. The assistant guides them to breathe at a specific pace thanks to ambient light brightness variation of the cockpit and draws their attention towards potentially unseen information. To test and improve its design, we evaluated FOCUS in an A320 simulator with five qualified pilots. In these trials, FOCUS was positively welcomed by pilots as they perceived it as a valuable addition to the cockpit. These evaluations will guide further iterations of FOCUS design and support the understanding of human-AI teaming in the cockpit in subsequent studies.