"Top of descent may be calculated manually with considerable effort"

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Or by using a rule of thumb - e.g. if you desire a 500fpm rate of descent (1000ft every two minutes) then you need to multiply the number of thousand feet you need to descend (say, 12,000) by two and this gives you the number of minutes out from the destination you need to start descending (in this case 24 minutes).

So 24 minutes before your calculated ETA, you start descending. Not so hard, really!

(This is for VFR flight. No idea how IFR pilots do it) —Preceding unsigned comment added by 159.245.32.2 (talk) 03:40, 19 November 2009 (UTC)Reply