Abstract: A flight recorder (11) for a vehicle such as an airborne vehicle is provided in which various data is recorded, along with on-board time data (from 38) in order to be processed by ground based equipment (13). The on-board time data is synchronized by using a telemetry signal (DT) which is received by a ground based tracking system so that the timing of the events recorded by the flight recorder (11) may be synchronized with the timing of events recorded by the ground based tracking system. This combined data is provided to the ground based equipment (13) in order that the data at (12) obtained on-board the vehicle can be analyzed. By the use of digital techniques, various measurements, such as acceleration and angular rate may be accurately stored and reproduced. This arrangement reduces repeat costs for multiple tests and increases reliability of test data.