During the failure of both primary altimetry systems, what should you maintain to ensure proper vertical guidance?

• A. Maintain FL indicated on standby altimeter
• B. Descend to a lower altitude for safety
• C. Climb to a higher altitude with best clearance
• D. Monitor primary altimetry more frequently

Answer: (A)

When both primary altimeters fail, the standby altimeter becomes the sole reliable source for vertical position. The standby instrument is fed from a separate source and is designed to continue providing altitude information, so you should hold the flight level it indicates. Set the standby to the correct pressure reference (standard for flight levels) and maintain that level to preserve proper vertical guidance. This keeps you at a safe, predictable altitude while you address the outage; descending or climbing without a valid altitude reference would compromise safety, and watching the primary instruments won’t help if they’re not functioning.