How many Altitude Alerters are required for RVSM?

How many Altitude Alerters are required for RVSM?

• A. 0
• B. 1
• C. 2
• D. 3

Answer: (B)

RVSM requires an alerting capability to warn the crew if the aircraft drifts from its assigned altitude while operating in reduced vertical separation airspace. One altitude alerter is specified to provide timely alerts to both pilots. The safety and redundancy come from having two independent altitude‑keeping systems, not from having multiple alerters. Zero would leave no alert, while two or three alerters would be extra beyond what RVSM requires. So one altitude alerter is the required number.

RVSM requires an alerting capability to warn the crew if the aircraft drifts from its assigned altitude while operating in reduced vertical separation airspace. One altitude alerter is specified to provide timely alerts to both pilots. The safety and redundancy come from having two independent altitude‑keeping systems, not from having multiple alerters. Zero would leave no alert, while two or three alerters would be extra beyond what RVSM requires. So one altitude alerter is the required number.