What is the maximum rate of descent in an instrument approach?
ICAO Doc 8168 stipulates that for a non-CDFA non-precision approach, the aircraft should not exceed 15% gradient when descending from FAF to MDA.


  1.7.4 Stepdown descent
  The third technique involves an expeditious descent and is described as “descend immediately to not below the
  minimum stepdown fix altitude/height or MDA/H, as appropriate”. This technique is acceptable as long as the achieved
  descent gradient remains less than 15 per cent and the missed approach is initiated at or before the MAPt. Careful
  attention to altitude control is required with this technique due to the high rates of descent before reaching the MDA/H
  and, thereafter, because of the increased time of exposure to obstacles at the minimum descent altitude.