Which mode of IFF is set prior to takeoff by maintenance personnel?

The correct choice, Mode 2, is used primarily for identification of friendly aircraft by air traffic control and ground-based radar systems. Prior to takeoff, maintenance personnel set this mode as it is designed for military use, allowing for the identification of aircraft within a specific operational area, particularly during missions where friendly identification is crucial. Mode 2 provides a unique code that is assigned to specific aircraft, facilitating their identification and ensuring safety and coordination within the operational environment.

In contrast, Mode 1 is more limited in application, generally used for aircraft identification that doesn't require the level of specificity and security that Mode 2 offers. Mode 3/A functions primarily for civil aviation, focusing on air traffic control rather than military identification. Mode 4, which employs encrypted responses, is intended for secure missions and typically activated under different circumstances than standard pre-flight checks. Each mode serves its specific purpose, but for pre-takeoff settings related to military operations, Mode 2 is the appropriate choice.