CoastalDriver wrote on Nov 28^th, 2011 at 10:55pm:

The answer is quite simply you match your ROD to the IAS GS - How? You divide IAS GS speed by 2 (and add a zero) to give you the required rate of descent to stay on profile, hence: If you descending at 300 kts then your ROD is 1500 fpm if your descending at 225 kts then your ROD is 1100 fpm if your descending at 200 kts then your ROD is 1000 fpm if your descending at 180 kts then your ROD is 900 fpm if your descending at 150 kts then your ROD is 750 fpm and, if your at 120 kts your ROD is 600 fpm.

Another great post. But I'd make that 'IAS' a 'GS' (for groundspeed) since, otherwise, you will not fly a 3 degree approach but something else in a more pointed angle, especially when starting high, where your IAS reading is low.

As an example, I'm currently at FL330, IAS is 270 kts, GS is 513 and the only speed defining how fast I get closer to my destination is the GS. If the winds change, my IAS will stay the same, but my GS will change, I would have to recalc my VS setting. That's the spirit.

So my initial descent rate would be approx 2500 ft/min (5 times GS or /2 + '0') and not 1350 ft/min (270/2 + '0') as your current text explains it. That's a 3 degree angle with the 2500 ft/min (which we are aiming for) and a 1.7 degree one with the IAS based method. Therefore, you will end up being too high when taking the IAS readout as reference.


To windplayer's and Pina's post. I must admit that I have a ton of respect for the guys really flying the dead reckoning in the sim. It can be very rewarding when the navigational instrument (stopwatch) and an aware pilot succeed on finding the right spot to land or navigate further from.  :)
Even more respect when flying with some rw injected weather.