The objective of this study is to develop statistically significant models in order to determine the effects of altitude on fuel consumption of commercial aircraft during descent for a specific flight-path angle. In this context, the fuel usage trend during descent is investigated for a constant flight-path angle as a function of altitude. For this purpose, flight data records related to ten randomly selected flights are used. To perform the investigation, three model approaches are discussed. In the first method, all descents are evaluated separately. In the second method, all data are evaluated and a general model is established. In the last method, the coefficients found for the models of the first method are examined and a profound relationship is established. For comparative purposes, the results of all approaches are evaluated by statistically determinative indicators and Base of Aircraft Data models. In conclusion, significant relationships between the fuel flow rate and the descent altitude for a 3 flight-path angle are obtained for all models for descents of 70% of the domain. As expected, the best results are found for the first model approach. Standard errors are found between 1.3 and 4.7% of the actual fuel flow rate for corresponding descent altitudes.