Originally Posted by Bleve
My experience is that some pilots don't fully understand the true significance of a sudden outside air temperature rise
You are not even avare of how thrutfully you have spoken.
Originally Posted by Quantz
Flying from Buenos Aires we overflew Rio de Janeiro and followed the same route that AF474 was flying when the accident happened. Crossing the ITCZ at FL370 with moderate to heavy turbulence in a 1-2 minutes period we experienced a sudden increase in air temperature, from -48ºC to -19ºC.
Using my faithful Felsenthal MB-2A (it gives very good results for troposphere which start diverging above tropopause but not by much), I estimate that your density altitude would jump from appx 37600 to 40100 ft, provided there were actual temperature rise.
Originally Posted by Capt Kremin
I was crossing the ITCZ a few years ago at FL390 and flew into a green radar return. The OAT before entering was -56C. In a few seconds it had risen to -28C. We received a message from out FMC that we were cruising above Max Flight level. The ride however was smooth and the aircraft, a 767, coped well. Flying out of the cloud brought an instantaneous reduction in Temp back to -56C.
Tim Vasquez may be a fine meteorologist, but he doesn't know everything.
And that makes density alt jump from 38900 to 42300 ft. Now ask yourself whether your wings would support at your new density altitude and whether your engines would give you enough trust to serenely cruise along. Tim Vasquez knows enough to state with confidence that thermal bubbles with 20-30 K higher temp than surroundings are thermodynamically severely improbable or, in layman's terms, impossible.
Congratulations fellows, you have witnessed very rare phenomenon. What you've seen was false excessive TAT reading, probably caused by TAT probe blockage, probably caused by ice cristals in cirruses. All we currently have about it is anectodal evidence that suggests that it happens very, very seldom. Being shy an rare beast we know very little about its habits and habitat apart that it occurs in temperatures below -40°C where it's assumed that ice is too dry to stick to anything. We can only guess that under certain circumstances it can thrive on pitot probes too.
Regarding the AF447: we don't know yet if it actually entered the CB or not so asking why did it enter the CB is pointless. Our only hope of finding out what exactly happened is recovering the CVR and FDR in good shape. And very, very, very thin hope it is. Oh, and IR needs TAS input to keep itself upright.
Photos show the composite tailfin with rudder still attached. Obviously it floats so currents have moved away it from the original splashdown point. Also apparent lack of damage on the side and leading edge has some implications but I don't intend to be the first one to write it down on the PPRuNe.