Which warnings are not inhibited when a DCU disable switch is pressed?

• A. EGPWS/ TCAS
• B. GPWS/ Engine
• C. ADIRS warnings
• D. All warnings

Answer: (A)

When the DCU disable switch is pressed, most non-essential warnings are suppressed to reduce cockpit chatter, but safety-critical alerts remain active. The ones that must stay audible and visible are the terrain awareness and collision avoidance alerts: EGPWS and TCAS. These systems warn you of immediate dangers—terrain ahead or another aircraft in the vicinity—so they’re designed to override suppression and keep pilots informed. That’s why the correct choice is the EGPWS/TCAS warnings. Other warning groups, such as older GPWS, engine, or ADIRS warnings, can be inhibited under this switch, so they aren’t guaranteed to remain active.