Over the last years, different airlines have suffered difficulties to rotate the aircraft during the take-off run. The incidents have been reported for various aircraft types, mainly aircraft with unpowered flight controls and low-medium rotation speeds that have been treated with anti-icing fluids. The pilots typically reported these incidents as difficulties or incapability to rotate the aircraft at Vr.
The Swedish accident investigation body investigated a related serious incident and made safety recommendations to EASA, among them to request the assessment of the aircraft manoeuvrability during take-off after the application of anti-icing fluids. This safety recommendation triggered this research activity.
The DIFT research project aimed to replicate the phenomena, understand the causes of the reported events and establishing the most adverse conditions. In the research project, an aerodynamic model representing a horizontal stabiliser was exposed to an accelerated stream in a wind tunnel modelling the actual conditions of a typical aircraft during a take-off run. The stabiliser lift and elevator hinge moments were measured over time and compared with the values for the untreated surface, to assess the impact of the applied anti-iced fluids. The results obtained during this research have qualitatively replicated the effects reported by the pilots.
The cognitions gained from the results of the project will be presented in the SAE G12 Committee for further consideration and will support future EASA rulemaking action aiming to request during airplane type certification the assessment of the fluids’ effects on aircraft performance.