FAA AMT Airframe Test 2026 – 400 Free Practice Questions to Pass the Exam

Over pressure event of the aircraft oxygen system in transport category aircraft can have various signs and cues. One of them, indicated in option C, is the missing green thermal expansion disk. The green disk acts as a safety valve and it is designed to burst and release excess pressure if the oxygen system experiences a sudden increase in pressure. If the disk is missing, it suggests that the pressure reached a critical point and the disk was forced to rupture. Options A and D may also be indicators of over pressure, but they are not specific to the oxygen system and could be caused by other factors. Option B, a whistling noise from the safety valve, could occur during normal operation and does not necessarily indicate an over pressure event. Therefore, option C is the most accurate answer.