The combustion of low-exothermic compositions based on sodium chlorate and metal fuel similar to those used in emergency oxygen generators for aircraft is studied. The specific system investigated is a powder mixture of sodium chlorate (NaClO3, >90 wt.%) and tin (Sn, <10 wt.%), with small (<2 wt.%) quantities of a transition metal oxide catalyst (Co3O4) which promotes decomposition of the chlorate. The synchronized experimental data on time-temperature history of the process (both in sample volume and on surface), instantaneous front velocity and product oxygen flow rate are obtained. The influence of reaction mixture characteristics (composition, metal particle size) on the process parameters is investigated. The combustion process is characterized by significant oscillations of the product oxygen flow rate. It is shown that the gas flow fluctuations are caused by unstable reaction front propagation. Analysis of the results suggests that the coupling of two low-exothermic reactions (i.e., chlorate decomposition and metal oxidation) connected by production/consumption of oxygen, is responsible for the observed instability of combustion wave progagation.