In RVSM, if one primary altimeter fails, what phrase should be reported to ATC?

• A. For information, operating on one primary altimeter only
• B. Negative RVSM
• C. Altimeter failure
• D. ATC cooperation requested

Answer: (A)

In RVSM operations, you must have two independent primary altitude measurement systems. If one primary altimeter fails but you still have a functioning standby and the other primary intact, you report to ATC with the exact phrase: “For information, operating on one primary altimeter only.” This communicates clearly that you’re not within the RVSM requirement of two functioning primary altimeters, but you’re continuing to operate with the remaining source. It’s an informational notice, not a request for a change in clearance.

This phrasing is preferred because it precisely conveys the situation without implying a complete altimeter failure or asking for specific ATC actions. Other options are less precise: “Negative RVSM” would imply a broader loss of RVSM status, which isn’t the standard immediate report for a single altimeter failure; “Altimeter failure” is too vague when only one primary unit is inoperative; and “ATC cooperation requested” doesn’t provide the specific status to ATC that you’re operating on one primary altimeter.