When should an AED be used on a passenger?

Using an AED (Automated External Defibrillator) is a critical intervention in emergency situations involving cardiac arrest or distress. The correct answer emphasizes that the device should be utilized when a person exhibits signs of cardiac distress and is unresponsive. This aligns with the established protocol in emergency response scenarios.

When a person shows signs of cardiac distress—such as chest pain, shortness of breath, or other related symptoms—it's vital to assess their responsiveness. If they are unresponsive, it indicates a potentially life-threatening situation where every second matters. The AED can analyze the heart's rhythm and, if necessary, provide a shock to restore a normal heart rhythm.

The other choices are less about the appropriate timing for AED usage and don't reflect the urgency and criteria set out in emergency response guidelines. Complaining of dizziness or feeling faint does not necessarily indicate a need for an AED unless accompanied by unresponsiveness or other severe symptoms. Routine check-ups do not warrant the use of an AED, as it is not intended for use in non-emergency circumstances. Thus, the correct answer emphasizes the specific situation where the AED is necessary: during severe cardiac distress when the individual is not responsive.