Fiber Bragg gratings (FBG) are a promising basis for sensor-based measurement of strain and begin more widely used in measuring systems for different designs. This paper examines the possibility of using FBG in the built-in control system designs from polymeric composite materials (PCM) in a number of industries, in particular for structural elements of aircraft. There discuses two methods of strain measurements for PCM structures using fiber-optic sensors on the examples of standard samples and a three-stringer panel of carbon plastic. The first method is based on calibration by strain gage and has an inaccuracy of 6%. This technique is recommended for standard samples, for example, used to determine properties of PCM. The second method is a modified version of the first and based on the calibration of strains obtained in the result of theoretical calculations using computer-aided software. The method has an inaccuracy of 9%. A modified version of the calibration has the advantage that does not require the structure destruction and allows calibrating the design with the hard to reach places. In the case of aviation equipment, this method can be used during the strengthening test at the stage of certification. The modified method is recommended for the system of built-in control to obtain strains and loads of the PCM-structures.