Which type of emergency equipment is always required on passenger aircraft?

Oxygen masks, life vests, and fire extinguishers are essential components of safety equipment required on passenger aircraft for several critical reasons.

Oxygen masks are crucial because they provide supplemental oxygen to passengers and crew in the event of a cabin depressurization, ensuring that individuals can breathe adequately until the aircraft descends to a safe altitude. Life vests are life-saving devices required for over-water flights, allowing passengers to stay afloat in the event of an emergency landing in water. Fire extinguishers are vital for handling small fires that may occur onboard, giving the crew the necessary tools to manage a fire before it escalates into a more significant threat.

This combination of equipment is fundamental for ensuring passenger safety during emergencies, adhering to aviation safety regulations that mandate these items be onboard all commercial flights. The other options, while they may include useful safety items, do not cover the full range of emergency preparedness required by regulations.