How many altitude reporting transponders must be operational for RVSM compliance?

For an aircraft to be compliant with Reduced Vertical Separation Minimum (RVSM) altitudes, it is necessary for at least one altitude reporting transponder to be operational. This requirement arises from the need for accurate altitude information to maintain safe separation between aircraft flying at higher altitudes, where the vertical separation is reduced to as little as 1,000 feet.

An operational altitude reporting transponder ensures that the aircraft's altitude is accurately transmitted to air traffic control (ATC), which is crucial for maintaining the integrity of the RVSM airspace. Although having two operational transponders is a best practice to enhance redundancy and reliability, the minimum requirement for RVSM compliance is one functioning transponder. This ensures that even in the case of failure of one unit, the aircraft can still comply with the RVSM regulations to maintain safe operation in this airspace.

The options indicating that two or three transponders are required misinterpret the RVSM compliance regulations, as does the option suggesting that there are no requirements at all. Understanding this fundamental requirement is key for pilots and operators flying in RVSM airspace.