The method involves determining the distance between a separable external load (A1) i.e. air-air-rocket, and a stationary, non-separable external load (A2) e.g. bomb, in an airplane or a missile during a separation procedure by using passive magnetic field sensors (MS1, MS2). The magnetic field sensors are arranged at the load (A2), and magnets (MAG) are arranged at the load (A1). Minimum distance is directly determined from a signal or the magnetic field sensors on the basis of calibration.