meekmok
rate of descent. - not accurate.
if it had been in cruise when the aircraft or crew had a catastrophic event it would have been in trim with an ias of around 280knots. Assuming both engines flamed out at the same time then it would have descended at 280 knots plus a bit because of the lack of thrust vector from the underslung engines.
This probably gave a ROD in the order of 3000fpm..which might have fractionally decreased as it came into ground effect.
If this didn't happen and it went into a spiral descent it would have broken up in the air.