COGNITIVE ENGINEERING CONSIDERATIONS 127 interactions and an implicit definition of the necessary underlying functionality. Cognitive walkthroughs (Lewis & Wharton, 1997; Smith, Stone, & Spencer, 2006) were then used to predict users’ interactions with this design. After refinements based on these walkthroughs, a functional prototype was developed that enabled more dynamic cognitive walkthroughs. This made it possible to easily explore a larger range of flights using actual data and also forced the design team to confront initially underspecified functional requirements. This prototype led to a design defined by several tabs. The Search Builder Tab (see Figure 1) serves as the Home Page and supports three different classes of users (single pilots, flight operators managing or instructing multiple pilots, and system analysts). It supports user interaction with the underlying data repository via forcing functions (options in dropdown menus mirroring repository data categories) and feedback to help users who enter something that the system does not recognize.