Air Accident Data Analysis, Modelling & Simulation Consultancy Report prepared for: Accident Investigation Board of Norway

The main aim of this study was to provide further insight into Loss of Control Inflight (LoC-I)/Upset events under icing conditions. The main objective was to identify the probable characteristics of a LOC-I/upset event due to tailplane icing for a business jet. Due to the lack of available (stability and control and aerodynamic) data for specific aircraft makes/models, a ‘generic business jet’ model was used for all analyses. It was not possible to replicate EXACT aircraft dynamics as evidenced by FDR data using modelling & simulation techniques. Flight data analysis was used to determine the flight conditions to be analysed and static and dynamic stability was assessed using established flight dynamics theory and modelling. The modelling and ‘what-if’ analysis therefore illustrates trends as a result of changes to selected parameters and not exact data. The degradation of tailplane aerodynamic characteristics due to icing was simulated using an assumed reduction in horizontal tailplane efficiency factor and classical theory supported by a commercial aircraft design software package. The results are only applicable for short time periods after a given disturbance since a linearised flight model was used about a given trimmed flight condition, no pilot control inputs were available (e.g. yoke pitch/roll, rudder) and no external (environmental) disturbance data were available (e.g. turbulence). The results demonstrate that the ‘generic business jet’ aircraft used in the analysis is statically and dynamically stable when horizontal tailplane efficiency is greater than 80%. When horizontal tailplane efficiency is reduced to 20% (simulating a ‘tailplane stall’), the aircraft is statically and dynamically unstable, smaller and shorter elevator commands produce large pitch responses and negative ‘G’ may be quickly reached within a short time period.