8.4 Crosswind Limits
8.4.1 The Manufacturer provides a value of the maximum demonstrated crosswind for dry and wet runways. This value is not a limitation as it is the maximum crosswind obtained during the flight test campaign at which the aircraft was actually landed. Operators have to use this information in order to establish their own limitation.
8.4.2 The maximum crosswind for automatic landing is a limitation.
8.4.3 In addition, the Manufacturer provides some recommendations concerning maximum crosswind for contaminated runways. These conservative values have been established from calculations and operational experience.
8.4.4 While operating aircraft on contaminated runways the crew is to refer the AFM to ensure that the performance limitations are not exceeded.
The crosswind limits for Canadian Runway Friction Index values are given at Appendix-‘B’
8.5 Performance Optimisation and Determination
8.5.1 The presence of a contaminant on the runway leads to an increased accelerate-stop distance, as well as an increased accelerate-go distance (due to the precipitation drag). This results in a lower takeoff weight which can be significantly impacted when the runway is short.
8.5.2 To minimize the loss, flap setting and takeoff speeds should be optimized. Increasing the flap and slats extension results in better runway performance but it reduces climb performance. An optimum flap setting should be chosen by referring to performance tables.
8.5.3 The takeoff speeds, namely V1, VR and V2 also have a significant impact on the takeoff performance. On contaminated runways, the take-off speeds are also a compromise between high speeds (for better climb performance) and low speeds for better field performance. In performance programs, used to generate takeoff charts, take advantage of the so called “speed optimization”. The process will always provide the optimum speeds. In a situation where the runway is contaminated, that means, as low as possible.
8.5.4 The FLEXIBLE THRUST principle, used to save engine life by reducing the thrust to the necessary amount, is not allowed when the runway is contaminated. Operators can take advantage of the DERATED THRUST.
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8.5.5 Pilots must remember that when using de-rated thrust recovery to full rated thrust is not allowed at low speeds.
8.5.6 However, the reduction of thrust makes it easier to control the aircraft should an engine fail (lesser torque). In other words, any time an engine is derated, the associated VMC (Minimum Control Speed) is reduced. This VMC reduction allows even lower operating speeds (V1, VR and V2) and, consequently, shorter takeoff distances. In a situation where the performance is VMC limited, derating the engines can lead to a higher takeoff weight.
8.5.7 Different methods are proposed to determine the performance on a contaminated runway. The methods differ by their medium (paper or electronic) and the level of conservatism and details they provide. The AFM is to be used to calculate the actual performance of the aircraft in the existing conditions.
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