aircraft. For redundancy purposes, temperature sensors have also been added in the A350 fuselage.
Fig.5 Example of A380 Multi-Function Probes
2.5.1.4 Humidity Humidity sensors offer real opportunities to improve weather forecast on specific phenomena (clear air turbulence, icing, convection) and provide in-situ measures to evaluate climate changes. Only few aircrafts are already equipped with humidity sensors in Europe but WMO initiative E-AMDAR promotes the integration of hygrometric sensors to improve weather forecast. There are few humidity sensors integrated in European commercial aviation yet but offer a real interest to improve weather forecast. This section will first specify the needs in term of performance and then detail two available humidity sensors integrated in American commercial aviation for AMDAR operating system.
2.5.1.5 Onboard Weather radar Weather radar is designed to detect precipitation: it helps to identify that associated with the most active convective cells in order to avoid the dangers associated with them (turbulence, hail and lightning). Weather radar can detect water in liquid form, such as rain and wet hail. However, it hardly detects water in solid form such as dry snow and ice crystals. It can partly detect dry hail depending on the size of the hailstones. In a convective cell, in the part situated below freezing point (0 °C, that mean FL 75 in standard atmosphere), liquid precipitation constitutes the most reflective areas. Below -40°C (at FL 275 in standard atmosphere) water no longer exists in general in a liquid state. In the part of the cumulonimbus between freezing point and the altitude where the temperature
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