What do stand-by instruments provide when the main displays fail or are unreliable?

• A. Navigation data and airspeed trends.
• B. Essential attitude, altitude, and airspeed information.
• C. Weather information for the flight path.
• D. Engine performance indicators.

Answer: (B)

When main displays fail or are unreliable, pilots rely on stand-by instruments to keep the airplane under control. The purpose of these instruments is to provide the minimum, essential flight data needed to fly safely. The stand-by attitude indicator shows the aircraft’s orientation relative to the horizon, giving you pitch and bank information to maintain proper attitude. The stand-by altimeter provides altitude information so you can maintain the assigned flight level and ensure terrain clearance. The stand-by airspeed indicator shows current speed, which is crucial to avoid stalls or overspeed and to manage maneuvering margins. Together, these three items give you the core situational awareness you need during degraded- display conditions, powered independently from the main displays so they stay available if the primary systems fail. Weather information and engine performance are not provided by stand-by instruments; weather data comes from weather radar and related systems, and engine performance is shown on engine instruments and ECAM/EICAS.