Whether this crew was responsible for their foray into the hail, and that might be the case if other aircraft were deviating, they will be busy explaining their decision and actions. I will not be charitable in saying that they demonstrated superior airmanship (gender neutral) nor will I condemn them for proceeding, when in retrospect a deviation would have been the more conservative course of action.
Hail is very difficult to detect with airborne weather radar, when above the freezing level. Wet hail is the most reflective type of precipitation, while dry hail, that is completely frozen hail, does not reflect radar energy. Hail shafts are often separated from the main body of the storm by several miles. A rule of thumb is for each knot of wind at altitude the hail will be displaced 1 nautical mile.
With X-band radar (which is what most airliners use, United uses C-band) the hail will show as a tiny blip and when the radar is set to a long range, as is common in cruise, ‘twon’t show up at all.
The accidents of EAL 66, PAA 759, and DAL 191, were related to wind shear and not hail damage. Wind shear in the form of microbursts does not require a thunderstorm but merely convective activity. The Southern accident (242) is a perfect case history of flying into a radar shadow, where the precipitation is so intense that even radar energy can’t get through.
These events happen from time to time, it’s important to learn from them and not jump to conclusions. When they do happen it is necessary to remain cool like the Southern captain, who reported to ATC when he had the second engine failure: “We just lost our second engine, I don’t need to tell you the implications of this because we only have two engines.”
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