The combination of ultra-low-power wireless communications and energy harvesting enables the realization of autonomous wireless sensor networks. Such networks can be usefully applied in commercial aircraft where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance. This paper presents, for the first time, a complete energy-autonomous wireless strain monitoring system for aircraft. The system is based on a multimode wireless time-division multiple access (TDMA) medium access control (MAC) protocol that supports automatic configuration and a time-stamping accuracy better than 1 ms. The energy supply depends solely on an innovative thermoelectric energy harvester, which takes advantage of the changes in environmental temperature during takeoff and landing. The system was successfully integrated and passed the functional and flight-clearance tests that qualify it for use in a flight-test installation.