Modelling the impact of speed variations on aircraft fuel flow rates and emissions

Abstract Implementing operational improvements within air traffic management offers a practical approach, as such improvements do not require major changes to infrastructure or existing systems. In particular, improving flight operations can help reduce fuel use and emissions. This study investigates the relationship between cruise speed manoeuvres and the resulting changes in fuel flow rate and emission indices. To this end, regression models are developed to predict changes in total aircraft fuel flow rate and the emission indices of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides ( normal upper N normal upper O Subscript normal x N O x $\mathrm{NO_x}$ ) resulting from speed manoeuvres (acceleration and deceleration) during the en-route phase. The models are built using data obtained from flight data recorders covering various aircraft and engine types and a range of cruise altitudes. Using true airspeed (TAS) change as the sole explanatory variable, the baseline linear models achieve upper R squared R 2 $R^2$ values of 0.87 and 0.84 for changes in fuel flow rate and the normal upper N normal upper O Subscript normal x N O x $\mathrm{NO_x}$ emission index, respectively, while the corresponding quadratic models yield upper R squared R 2 $R^2$ values of 0.70 and 0.74 for changes in the HC and CO emission indices. Multivariable models incorporating flight level and aircraft type, together with pre-manoeuvre values of aircraft mass, TAS and ambient temperature, provide little improvement for fuel flow rate and the normal upper N normal upper O Subscript normal x N O x $\mathrm{NO_x}$ emission index but modest improvements for HC and CO. Direction interaction models, however, improve fuel flow and normal upper N normal upper O Subscript normal x N O x $\mathrm{NO_x}$ predictions, indicating that acceleration and deceleration are not fully symmetric. The findings may enable more accurate predictions of fuel consumption and emissions, improve aircraft cruise speed planning and ultimately support efforts to mitigate environmental impacts.