Now I've never been in or seen one of these rapid descents but I'd be mightily surprised if this was not an extreme distortion of the truth (and very mischievous if so).
Like everything in the aviation world, there are degrees. There are rapid descents and a million variations of....
Basically, you start with a healthy aircraft that for some reason decides to instantly depressurise at F400. The response (beyond the crew putting on their own oxygen masks, and doing a few other coughpit items), is to get the aircraft descending at max mach number/ias, idle, and max speed brake. Descent rates will be large (8000 fpm), and you'll be at the bottom in the minimum time.
Great. But is that a realistic scenario? Of course not. If the aircraft lost all the air that fast, it has to come from somewhere, so....
The next variation...
The air went away really fast...so there must be a big hole, so the structure may be in doubt. Now you'll use max speedbrake (as you always will), but the IAS will be limited to, well, what's a good idea? The speed you were at is always a good start point. But, less speed means less rate of descent, which means the cabin is higher for longer....
And in the middle....
What if, during the second example, you get an indication of a total loss of crew oxygen. Now, you are faced with the choice of risking the structure, whilst ensuring there is someone to drive it.
They are the real emergency descents.
Then there are a whole range of other scenarios in which it would be a good idea to go to 10,000 feet soon, but without huge urgency.
There are a million variations.
