Which actions are recommended when one primary altimeter fails within RVSM?

• A. Couple operating system with height lock
• B. Maintain increased vigilance regarding altitude
• C. Notify ATC 'For information, operating on one primary altimeter only'
• D. All of the above

Answer: (D)

In RVSM operations, altitude integrity is critical because two independent altimeter readings backstop safe vertical separation. When one primary altimeter fails, you still have a functioning reference, but you must raise vigilance and coordinate closely with ATC while you manage the loss of redundancy. Engaging the flight guidance system to maintain altitude helps prevent inadvertent climbs or descents caused by manual handling with a single instrument, using the remaining reference to hold a stable altitude and reduce drift. At the same time, you should routinely cross-check with the standby altimeter and other available indicators to catch any discrepancy early, since you no longer have dual independent readings to automatically validate altitude. Informing ATC that you’re operating with one primary altimeter only communicates the situation, enabling them to adjust spacing and accept any necessary routing or altitude accommodations while you work through the issue. Taken together, these steps provide the safest, most coordinated response in RVSM when a primary altimeter fails, which is why all of the above is the recommended approach.