What is the maximum allowable difference between two primary altimeters during checks?

The maximum allowable difference between two primary altimeters during checks is 200 feet. This standard is set to ensure that both altimeters provide a consistent and reliable reading, which is crucial for safe flight operations. Having both altimeters closely aligned minimizes the risk of altitude discrepancies that could lead to dangerous situations such as controlled flight into terrain or misjudging the altitude during critical phases of flight. Adhering to the 200-foot limit helps pilots maintain situational awareness and ensures that they are operating within safe parameters. This practice is part of regulatory requirements designed to enhance safety in aviation.