[Robe]

Lets do some math...
Cruise alt =39000ft(approx),
Impact Alt 6500ft (approx),
total Descent 32500ft(approx)
10min (approx)from cruise to impact
That comes out to about 3250ft per min decent
Normal descents are about 500 ft per min

Over 6 times the normal decent

[Moonman62]

Commercial aircraft usually start descent around 20 minutes before expected arrival time. The Flightaware chart shows a steady slope of descent. Flightaware data isn’t perfect, but it’s close.

[expat2]

500fpm is typical only for small, slow planes. An airliner is much faster and the same glide path might require up to 2000fpm.