A method in an aircraft for the validation of variable data is provided. The method comprises: receiving a request from an application program to retrieve data attributes for at least one data item to be entered via a GUI provided by the application program; requesting, from the flight management engine using an API, the data attributes for the at least one data item, wherein the data attributes identify at least one limit for data entry for the at least one data item including a minimum and/or maximum value for the at least one data item; receiving the requested data attributes from the flight management engine; and transmitting the data attributes to the application program; wherein the application program restricts data entry for the at least one data item in conformance with each limit provided by the data attributes for the at least one data item.