This paper presents the current state of the research on the on-board recording system application for the detection of critical situations in railways. The estimation of the rail vehicle state is based on signals registered by using a specialized on-board device. The critical situation of a rail vehicle can consist of diesel locomotive engine dysfunctions, high vibrations, exceeding of limit velocity, acceleration or inclination. The monitoring of the vehicle state needs a set of sensors. The movement parameters are acquired from a GPS device, accelerometers and gyroscopic MEMS sensors. Especially interesting here is the application of GPS signals, because GPS not only gives a geographical position, but also the vehicle velocity. The accelerometer sensors which measured the acceleration in three perpendicular directions were assigned to operate together with GPS in order to establish the vehicle position and for the detection of exceeding any limit acceleration value. The gyroscopic MEMS sensors support the position and route detection and also show any exceeding in vehicle limit inclinations. Additionally, some accelerate sensors record the vibroacoustic signals taken from chosen places on the engine body or other vehicle parts for the assessment of the engine state, particularly in terms of potential failures. The analysis of the additional acceleration signals was performed using specialized signal processing methods and some specialized algorithms based on artificial intelligence (e.g. Fourier analysis, wavelets, nonlinear methods based on deterministic chaos theory, short time methods and support vector machines). The first results are promising and show the possibility of using the above described approach to detect the combustion locomotive state.