What is the purpose of the stand-by flight instruments and when are they used?

• A. They monitor fuel quantity and fuel temperature.
• B. They provide essential attitude, altitude, and airspeed information if the main flight deck displays fail or are unreliable.
• C. They display passenger information.
• D. They control cabin lighting.

Answer: (B)

Standby flight instruments are the backup set of essential flight data that keep the crew informed when the main cockpit displays or the data feeding them fail or become unreliable. They provide attitude (the artificial horizon), airspeed, and altitude information, using an independent power source so they remain usable even if the primary electrical system or avionics are inoperative. This allows the pilots to maintain safe control of the aircraft and continue flight or perform an orderly approach while the main displays are restored or an alternate plan is followed. Other cockpit data like fuel quantity/temperature, passenger information, or cabin lighting are handled by different systems and are not part of the standby flight instruments.