I remember my mother referring to "air pockets" when I was a kid (she was a very nervous passenger), and I now know the technical term: CAT, but I've always wondered what it actually is?
As I see it, the possibilities for causing sudden loss of altitude are:
1 - A "pocket" of low-pressure air, causing loss of lift (would also cause lowering of IAS since the density of air hitting the pitot is lower).
2 - A downward-flowing column of air, so the aircraft still has the same lift (and IAS) and is flying straight-and-level, but the air it's flying through is going down taking the aircraft with it.
3 - Sudden tailwind, causing loss of IAS and lift.
Any others?
Does anyone know which of these is involved in CAT?
I don't suppose anyone looks at the IAS indicator when this sort of thing happens? :-)