Stability, Cloud Development, and Precipitation

Hazardous aspects of hail in aviation.

Hailstones are pellets of frozen precipitation that vary in shape and size. Hailstones form in the cumulonimbus cloud during moderate to severe thunderstorms. The formation of hailstones requires a part of the storm cloud to be below freezing as well as all of the "ingredients" for a thunderstorm: continuous updrafts, sufficient moisture, and a lifting mechanism. As growing ice particles pass through regions of varying liquid water content, a coating of ice forms around them, causing them to grow larger and larger. In a strong updraft, the larger hailstones ascend very slowly and may appear to “float” in the updraft, where they continue to grow rapidly by colliding with numerous supercooled liquid droplets (Ahrens & Henson, 2018). When the hailstones become too heavy for the updraft to support, they fall from the cloud.

Hail can be extremely hazardous and according to the textbook, "Deaths due to hail are somewhat more frequent in parts of Asia, where 92 people were killed in the Bangladesh thunderstorm of April 1986..." (Ahrens & Henson, 2018). Hail poses a large threat to aircraft because hail can cause severe structural damage to a plane. Hail can leave dents, break windows, and even destroy plane engines. The amount of damage depends on the hailstone size, the velocity at which it falls, and the wind speed associated with the thunderstorm producing the hail.

On April 4, 1977, an aircraft was forced to land on a highway after suffering severe hail-strike damage resulting in the loss of thrust in both engines. The crew had been advised of the presence of thunderstorms and the possibility of tornadoes along their route of flight, but they were not informed that the storm cells had formed a squall line. The crew proceeded with their flight and attempted to pick a flight path through what they thought was a low-intensity area, but was really the main activity point. It was later discovered that the crew had been misled by their radar. As the aircraft descended from its cruising altitude, it entered a thunderstorm cell and encountered a massive amount of rain and hail. The hail was so intense that it broke the aircraft's windshield, and because of the ingestion of both water and hail, both engines became severely damaged and underwent flameout ("Southern Airways Flight 242", 2020).

References

Ahrens, C. D., & Henson, R. (2018). Meteorology Today: Introductory Weather Climate & Environment, 12th Edition. Mason, OH: Cengage Learning.

Southern Airways Flight 242. (2020, November 19). https://en.wikipedia.org/wiki/Southern_Airways_Flight_242

The Weather Channel. (2014, December 23). Why Planes Crash: Hail Brings Down Plane. Retrieved from https://youtu.be/wTytGeohjR0