Weather Hazards - Hail

All weather hazards could mean a greatest risk to aviation operations, however, in my post I have chosen to speak about hail. Hail is part of the category of Thunderstorms, which are categorized as hazardous by the DOT (2013), as they can result in an aircraft accident and deaths for passengers and crew on board. Hail falls under the “single cell” category, as on hot and humid summer days, a single cell (or common) thunderstorm cell will frequently form. These cells have the potential to be severe, producing hail and microburst winds.The most dangerous thunderstorm threat to airplanes is hail, which competes with turbulence. Drops that have been supercooled above the freezing point begin to solidify. When a drop freezes, subsequent droplets latch on, causing the hailstone to expand (sometimes even into a massive iceball). Severe thunderstorms with powerful air currents that have risen to enormous heights generate massive hail. These will inevitably fall, and  may be seen in the skies several miles away from the thunderstorm.

Hail originates in severe thunderstorm, specifically those with vigorous updrafts, a high fluid water content, a considerable vertical extent, big water droplets, and a large percentage of the cloud layer that is below freezing 0 °C (32 °F). Strong air currents of this magnitude might also imply the proximity of a tornado.

Firstly hail is detrimental to aviation operations due to Precipitation Static. Precipitation static is created when an aircraft collides with uncharged particles while in flight. Hail is one of these particles. When the aircraft collides with these neutral particles, the positive component of the particle is deflected away from the aircraft, while the negative component sticks to the aircraft's skin. A significant negative charge will form on the aircraft's surface in a relatively short amount of time. When a significant negative voltage level is attained, the aircraft could produce static in the airborne radio equipment if it is not equipped with static dischargers or has an inadequate static discharger system.Radio interference can endanger aircraft safety by interfering with communications and navigation systems. Secondly, hail can create serious damage to aircraft and result in crashes and fatalties

In order to avoid thunderstorms and therefore hail, pilots must follow general rules set by the FAA. Firstly they should avoid all thunderstorms, secondly, they should never approach any visible storm cloud with overhanging portions closer than 5 miles, and consider extending that distance to 20 miles or more. This second rule specially applies to hail as hail and violent turbulence can be encountered as far as within 20 miles of very strong thunderstorms. Pilots should promptly lower airspeed at the first hint of turbulence to the maker's suggested airspeed for turbulent air penetration for that same gross weight. Pilots must also not attempt to flight beneath thunderstorms (due to destructive potential of shear turbulence). In addition, if a thunderstorm has been entered pilots must maintain a straight and level altitude, using a heading that will take them out of the thunderstorm as fast as possible.
Pilots are also able to utilize the Weather Radar System, which detects and displays significant weather in their route, measures rainfall density, increases aircraft utilization and overall provides a safer flight.
References:
FAA. (n.d.). Potential Flight Hazards. ENR 5.7 potential flight hazards. Retrieved March 10, 2022, from https://www.faa.gov/air_traffic/publications/atpubs/aip_html/part2_enr_section_5.7.html
FAAS Team. (2008). Thunderstorms— Don’t Flirt...Skirt ‘Em. Federal Aviation Administration. Retrieved March 10, 2022, from https://faasafety.gov/files/gslac/library/documents/2011/Aug/56398/FAA%20P-8740-15...
US DEPARTMENT OF TRANSPORTATION. (2013). AC 00-24C - thunderstorms - federal aviation administration. Retrieved March 10, 2022, from https://www.faa.gov/documentlibrary/media/advisory_circular/ac%2000-24c.pdf

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