Hudson,
With full power I would be very surprised if a B737 could not easily exceed the speed of sound even in a 30 degree nose down attitude. As stated before VMO/MMO is not breakup speed which would be well in excess of VMO?MMO. Boeing should have a good idea of that and it would vary depending on whether G loading was applied or whether excess speed in an "unloaded" profile was the reason for the ultimate event.
Maxflex55 says that 50000 feet per minute in a vertical descent is less than the speed of sound but that only represents the VERTICAL component of the descent. Shallower dive angles will need a higher speed to produce a VERTICAL component of 50000 feet per minute.
Taking the case of a 30 degree dive angle a speed of 986kts would be required to give a VERTICAL component of 50000feet per minute. Well in excess of M 1.0 at whatever the local temperature was.
Likewise a 45 degree dive angle needs a speed of 697kts to get the same result and at 60 degrees dive angle speed required would be 569kts.
So it was possible but the dive angle may not have been constant and only a FDR trace of appropriate parameters could yield accurate data.
PS Forgot to add:
Using Maxflex's M1.0 of 613kts at 20000feet and assuming M1.2 which is 737kts a 42 degree dive angle would suffice. (Just a coincidence the 737 bit...cheated by the odd knot!)
[ 20 July 2001: Message edited by: pterodactyl ]