The good thing with thunderstorms is that they are easy to spot, be it visually by day, or by aircraft weather radar when in clouds, or at night.
The very bad thing about the is that they represent an extreme danger to planes, and can not be flown through. Never. The dangers found in them are turbulences, with updrafts and downdrafts strong enough to literally break any plane in pieces. You must imagine that a typical CB is 10 kilometers wide, can be up to 12 km high, and contains an enormous ammount of energy. Winds in in can have vertical speeds of dozen of meters per seconds, and change radically over meters only.
Another danger present in CBs are hailstones. Ok, you just think now of the size of hailstones you know from your ground experience. But the one you can "meet" on ground are already parlty melt because of their descent time. The hailstones within a CB can be as big as grapefruits or ananas... and fly horizontally in strong winds.
Recently, and easyjet boeing 737 has been hit by a hailstorm, without actually flying in a CB. The crew declared emergency and came back for immediate landing. Strangely, neither airborne weather radar nor ground based weather radar did detect that sudden storm.
The following pictures will give you an idea how the plane was damaged. Nevertheless, the crew could fly it back normally, but obviously the co-pilot (sitting right) had to land.
And once again, this plane did not flew through a thunderstorm, it has "only" be hit by a hailstorm.
I have no pictures of planes that flew through a thunderstorm, because they dont. The normal distance that most of the companies require from their pilots is 10 nautical miles from the CB border, this is about 18 kilometers.
My personnal closest encounter with a CB was as a PAX, at night. There was a CB line on our flight path, it was a late flight, and the only alternate would have been one flying hour away. The captain did spot a hole on the weather radar... He used the public address to say "Cabin crew, take your seats... quickly". We had then two minutes of very severe turbulence. It was so severe that if someone had not been with seatbelt fastened, he would probably have been severly injured by hitting the ceiling. The atmosphere in the plane after that was suddenly very silent. After landing, I had a short chat with the captain, and asked him about the distance. His answer (which I beleive is true) is that we were 5 nautical miles (9 kilometers) from the CB's border.
Something additional, a friend operating in a local company told me that he once had a lighting strike while flying 10 miles (18 kilometers) away from the CB. This is usually not a problem, as planes are perfect Faraday cages. The only risk is damage to the radios, but a plane can not explode becose of a lightning strike.
An additional danger that is present in thunderstorms is icing, but I will say more on that on a later post.
One last thing about moderate to severe turbulence. In mid to large size airliners, the wings are flexible by design. Thus it is perfectly normal and safe to see the wings moving up and down in turbulence. There is an enormous safety margin in design, and I know no case of planes the have been "destroyed in the air" by turbulence... except the very few that flew through CBs.
