Power levers idle, prop levers full forward, flaps take off, gear down and airspeed max 180kts will give you a max rate of descent around 4500 - 5000 fpm, the vsi is on its stop and this rate of decent is approximate. The 180kts is the limiting factor that stops you from being able to point the nose lower to the ground and increase your rate of descent. This was the standard approach when flying into Iraq with the 1900