Effects of Descent Flight-Path Angle on Fuel Consumption of Commercial Aircraft

Abstract

In this study, the effects of the flight-path angle (FPA) ranging between 1.0 and 4.5 deg during a continuous descent approach, on certain fuel-related parameters such as fuel flow, fuel burn per 1000 ft of altitude, and specific range, are investigated. The dataset, obtained from Turkish Airlines, includes 4384 eligible flight data records of narrow-bodied commercial aircraft performing 9351 domestic flights between 30 city pairs, across Turkey. The results indicate that the fuel flow is a strong linear function of FPA up to 2.5-3.0 deg for all of the aircraft types, whereas the effect diminishes above 3.0 deg. There is a monotonic decrease of the fuel burn per 1000 ft of altitude with an increase in the FPA, with the trend being stronger than that for fuel flow. Even though the fuel consumption of the descent flight significantly decreases with steeper FPAs, the effect of the FPA on the total fuel consumption of the flight seems not as straightforward as it does when considering only the descent phase. A case study based on this model indicates a U-shaped pattern for total fuel burn with an increase in the FPA, in which the highest fuel saving relative to 1.0 deg of the FPA is calculated to be 14.0% (191 kg) at 2.5 deg of the FPA.