An Unfortunate Event
I think Taamguy and Dream Land both make excellent points.
In a potential crunch situation, Fly First. If, as this case suggests, a rapid descent to FL100 is necessary, start down, put the mask(s) on and then call ATC. Time is important. If a PAN or EMERGENCY call is even possibly warranted, skip the "Cool on the Radio" thing, make the declaration for God's sake, Tell ATC what problem is suspected. As once of these writer's notes, ATC's job is to provide separation - and they are darn good at it; they are not mind readers. I'd rather see a few a few more PAN/EMERGENCY calls that perhaps later get cancelled, than I would seeing accidents like this one, where we are still guessing about the cause - and the principals cannot tell us why they needed to descend. ATC's systems can and do identify/alert controllers to major variations in course or altitude and those folks are more than able to start getting others out of the way while they attempt to collect information. Sadly, we do not know what happened. Much of the speculation is probably close to the hard facts, but for some unknown reason, the pilots did not share much detail with ATC before they became unable to communicate. Assuming (admittedly a poor practice) that it was a pressurization issue and recognized by the pilot(s), instantly diving for FL100 and communicating in the way down does NOT violate any regulation that I've ever read. We may eventually know, but this airplane does not carry the same, high-end FDRs and CVRs standard on commercial transports, so even if the wreckage is located, it may not yield a lot of detail. For those lost, RIP; this loss **may** have been preventable. Sad.