Air transport development brings an increased focus on the safety of piloting. The safety conditions can be assessed by mental workload. Psychic discomfort or excessive stress on pilots can negatively influence the course of flights. Therefore it appears convenient to monitor such parameters, which represent the mental wellbeing, or discomfort of a pilot. Since physiological measurements can provide a good information about mental workload or stress, this work primarily focuses on the observation of the change in heart rate, as it is an indicator of stress during the training of pilots, using the designed modular telemetry system. Another aim of this study is to evaluate the influence of a change in the avionic data visualization. This can have an unfavorable effect on the piloting of an airplane. This work, based on the evaluation of heart rate shows, that the switch from analog visualization to glass cockpit creates increased levels of stress in pilots, which was proved for all examined subjects except one. Significant level of correlation in the heart beat rate change in subjects in the course of training was also discovered.