The AIM says: Descend or climb at an optimum rate consistent with the operating characteristics of the aircraft to 1000 ft above or below the assigned altitude, and then attempt to descend or climb at a rate of between 500 and 1500 fpm until the assigned altitude is reached. If at anytime the pilot is unable to climb or descend at a rate of at least 500 fpm advise ATC. I have heard of pilots being given a hard time from check airmen on IOE for initiating a slow descent at less than 1000 fpm. I'm just looking for anyone who has the written reference on where is says to descend at 1000 fpm or greater. Thanks for the help