Structural Health Monitoring (SHM) systems are vital for aircraft operation, and are becoming a promising technology, being currently considered for reference certification authorities such as the FAA (Federal Aviation Administration). Novel techniques for Non-Destructive Inspection (NDI) tasks could be devised, opening new possibilities for future implementation of in-flight systems to monitor aircraft structures. For this purpose, the development and evaluation of new, non-intrusive and lightweight sensors are of capital importance. In this context, carbon nanotube fibers have demonstrated to be highly sensitive to strain and are virtually non-intrusive, thus being potential candidates to be used as SHM sensors. Therefore, the present research work is devoted to the experimental assessment of sensors based on a single carbon nanotube thread, applied to monitor strains in metallic specimens under cyclic loads. The study includes the sensor description, as well as the lamination process and the experimental procedures. The results presented, which include comparisons with strain measurements obtained with two other techniques, show that the carbon nanotube-based sensors exhibit high sensitivity and provide good qualitative measurements. However, difficulties were found as related to imperfections of installation process and the occurrence of hysteretic behavior. The results also indicate that the sensors can be highly effective for the detection of fatigue cracks.