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The most typical aeronautics structure is a skin (plain or curved) reinforced with stringers and ribs. The main problem for this kind of structures is to verify the conditions of the bond line and to guarantee this joint during maintenance and certification tasks.

A reliable method to monitor debonding failures during the operational life of the airplane is proposed in this paper. The principle for this technique is to detect the differences of strains between two closely located sensors in loaded structure. Damage changes the stiffness and, for different applied loads, changes the strain field distribution in the structure. Unless the sensor is very close to the damage, the changes in strain readings use to be very small. The differential strain approach allows detecting damage at further distances. Fiber Bragg Grating sensors are used as high accuracy strain sensors.