Analysis of microphysical characteristics of icing clouds in Shaanxi and surrounding areas based on aircraft probing

In 2021, a series of 21 natural icing resource probing tests were conducted in the Shaanxi region and its adjacent areas using the King 350 aircraft. Through meticulous analysis of onboard Cloud Combination Probe (CCP) detection data, the intricate microphysical characteristics of icing cloud layers were meticulously investigated. Moreover, an in-depth evaluation of compliance with the airworthiness standard, CCAR-25 Appendix C envelope for transport aircraft, was undertaken. The findings reveal that throughout the course of the 2021 natural icing resource exploration tests, within the confines of the icing cloud layers, the liquid water content (LWC) remained below 0.15 g/m³ for 90% of instances. Notably, nearly half of the observed icing encounters exhibited an LWC below 0.07 g/m³. Median volume diameter (MVD) data illustrated that approximately 85% of samples fell within the 10 to 25 µm range, whereas instances of LWC surpassing 0.2 g/m³ were predominantly noted within the MVD values of 18 to 22 µm. Furthermore, the outside air temperature (OAT) typically ranged between −6 to −4 ℃, accounting for nearly half (47%) of the total icing exposure duration. Furthermore, the comprehensive analysis of icing encounters in the temperature range of −10 to 0 ℃ demonstrated a notable compliance rate below 40% for 97.3% of the samples, based on the criteria outlined in Appendix C. Similarly, within the −20 to −10 ℃ range, 91.7% of the samples illustrated a compliance rate below 40% for Appendix C envelope. While the Shaanxi region and its neighboring environs offer conducive icing meteorological conditions suitable for executing hovering flight within icing cloud layers to satisfy stipulated icing flight duration or thickness requirements, a discernible discrepancy remains when compared to the continuous maximum icing envelope mandated by CCAR-25 Appendix C. To comprehensively encompass year-round icing meteorological conditions, including those during summer and autumn, a further refinement of CCAR-25 Appendix C's envelope with respect to temperature and altitude parameters is strongly advocated. This study not only provides intricate insights into the microphysical nuances of icing cloud layers but also emphasizes the imperative for augmenting the representation of these complexities within airworthiness regulations and aviation safety protocols.