Flying through thunderheads
Responding to messages implying that airliners studiously avoid CBs:
As a scientist and relatively frequent SLF mostly in the US, I'd say that incidental CB penetration is fairly common. I've experienced many episodes over the years, usually at high altitudes when the PF is attempting to stay at the ATC assigned altitude and thread between overshooting tops hidden in the anvil cirrus. The last one was just a week ago over Colorado. As heard on Ch 9 on UAL, a missed ATC check-in led to confusion when the pilot requested a diversion around a CB. We were denied the turn and clipped the convective tower leading to violent updrafts and downdrafts for about 30 sec. Just about every flight over terrain in the southwest or anywhere in the southeast this time of year is a roulette wheel for convective excitement given the volume of air traffic around/over storms, and the Alps in summer speak for themselves. I think the biggest problem could be dry CB tops which don't show up well (or at all) on the WX radar (especially a problem over Africa, I gather). Flying through anvil cirrus or at night, I suspect the PF won't see it until the plane is inside it. Certainly, I have experienced night-time ITCZ CB penetration on the way to Australia where I saw the clouds and lightening prior to the turbulence. Of course, most of these are non-events in terms of fatal consequences (just a little more fatigue on the airframe and PF/CC/SLF nerves), but citing the manuals on CB avoidance doesn't seem to capture the true richness of today's flight environment. As to how CB penetration guidelines or lore may have contributed to today's tragedy, I only speculate, but normalization of deviance can be a killer.
Apologies for the non-pilot post - back to lurking...