How many FMSs must be available to utilize performance speeds?

To utilize performance speeds, it is essential to have two Flight Management Systems (FMSs) available. This requirement stems from the need for redundancy and cross-checking within avionics systems that manage flight navigation and performance calculations. Having two FMS units allows for real-time comparison and validation of data, which enhances safety and accuracy. This dual FMS setup ensures that if one system encounters a malfunction or provides erroneous data, the other can take over seamlessly, maintaining operational integrity and safety during flight.

In aviation practices, reliance on a single FMS would not provide the necessary level of confidence and reliability in critical performance speeds, making the availability of two systems a standard requirement for modern aircraft equipped with advanced flight management technologies.