I have heard many pilots state that a 3 to 1 ratio (that is - 3 miles to every 1,000 feet down) is sufficient to get a 500-1000 foot per minute descent.
so, using this formula, at 32 miles out, you should be starting to cross 10,600 feet.
descent planning is vital to most, if not all instrument approaches, especially for non precision ones. Say for instance, you are shooting a VOR approach, at at airport that is say, 10 miles from the VOR. You want to be in the area of 3,000 AGL, assuming that this approach has no minimums.
Light and slow aircraft generally use the same formula. The only difference would be the decent rate. for a piper or something along that line, the decent rate should be around 200-250 feet per minute, possibly even less.
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