The certification of retro-fitted structural health monitoring (SHM) systems for use on aircraft raises a number of challenges. One critical issue is determining the optimal means of supplying power to these systems, given that access to the existing aircraft power-system is likely to be problematic. Other conventional options such as primary cells can be difficult to certify and would need periodic replacement, which in an aircraft context would pose a serious maintenance issue. Previously, the DSTO has shown that a structural-strain based energy harvesting approach can be used to power a device for SHM of aircraft structures. Acceleration-based energy harvesting from airframes is more demanding (than a strain based approach) since the vibration spectrum of an aircraft structure varies dynamically with flight conditions, and hence a frequency agile or (relatively) broad-band device is often required to maximize the energy harvested. This paper reports on the development of a prototype vibro-impacting energy harvester with a ~59 gram flying mass and two piezoelectric bimorph-stops. Over the frequency range 29-41 Hz using a continuous-sine 450 milli-g r.m.s. excitation, the harvester delivers an average of 5.1 mW. From a random band-passed 25-45 Hz excitation with r.m.s. 450 milli-g, the average harvester output is 1.7 mW.