Aircrew MQF Practice Test 2026 - Free Aircrew MQF Practice Questions and Study Guide

Transponder codes, or squawk codes, let ATC know what state a flight is in even when voice communication isn’t available. When radio contact is lost, the aircraft switches to the code specifically designated for radio failure. This single code signals to ATC that there is no voice communication, so they rely on radar observations and predefined lost-communications procedures to manage the situation. That’s why it’s the best choice: it directly communicates the absence of radio contact, enabling the controller to adjust instructions and coordination accordingly.

Other common codes represent different scenarios: one indicates a hijack, prompting an immediate, security-focused response; another marks a general emergency, indicating a life-threatening or serious aviation situation. The remaining code is reserved for future use and isn’t used to indicate radio failure, so it wouldn’t convey the intended condition.