Tests of fatigue crack initiation are carried out on two different aluminum alloys by using low-cycle fatigue (LCF) data to predict initiation at notch tips with a radius between 0.1 and 10 mm. A comparison of the LCF properties of these alloys in terms of stress strain and cyclic plastic energy is made. Damage accumulation laws in the range of plastic strain and elastic stress are studied. Variable-amplitude loading represented by programmed blocks characterizing the standard TWIST flight loading are investigated. Fatigue crack initiation at notches is determined; initiation is detected by the electric potential method. It is found that the energy approach is an accurate method of determining a realistic cyclic mechanical behavior of aluminum alloys. Constant-amplitude loading of low ΔK (stress intensity factor range) that causes no crack initiation decreases the number of cycles to crack initiation, when the loading program is composed of a higher ΔK and this low ΔK to form block loading.