Hey guys, I recently bought the Coolsky DC-9 and it is great. But I am so use to computerized flight systems and because of this I have no idea when to start my descent in this thing (Kind of embarrassing). So as simple as it might be, I need a bit of help.

((cruise altitude - descend to altitude)/1000)*3=TOD in nm

 

I am cruising at FL490

 

Destination IF altitude is 4000'

 

49,000 - 4,000 = 45,000

 

45,000/1000 = 45

 

45*3 = 132

 

I want to begin my descent no closer than 132 nm from the IF.

 

Typically I will add 10 nm.

 

regards,

Joe

Try this rule of thumb. If you'd like something more, try searching the AVSIM File Library or Google "descent calculator" and you'll find plenty, many of which are freeware.

In general, you can use the 3-to-1 rule to determine when to descend. OR 3 miles to descend every 1000ft for a 3 degree descent.

 

You usually want to be at 10,000ft 30 miles from the airport.

 

So if you're at 30,000ft you start descending at 90nm from the airport.

 

An alternate method I use when I'm flying an aircraft and I descend in V/S Mode, is I plan to descend at 3,000fpm. I look at my GS. 600kts = 10 miles a minute. 420kts = 7 miles a minute.

 

So I start with 10000ft, whatever altitude I'm at say 37,000ft = 37-10 = 27,000ft to lose / 3,000ft/min = 9 mins.

 

If my ground speed is 420kts, then I start my descent at 9 x 7 = 63 miles from the point where I want to be at 10000ft 30 miles from the airport or 63 + 30 = 93 miles.

 

 

So that's the mental math I use to double check the FMS.

You could go old school for the old school aircraft...  3 nautical miles (nm) per 1000ft.  Just work it backwards to figure your Top of Descent.

 

Should do the trick for you.

3 times altitude.  If at FL350 = start down at 105nm from a sea level airport for a straight-in landing.

5 times ground speed.  If GS is 400 kts, then descent rate should be 2000fpm.

These values will change on the way down, so recalculate every 3-5 thousand feet during descent.

 

jetjerry

Thanks guys I also found a cool website that does it for you http://aerotexas.com/desplan/desplan.php

I know a guy who flew the old Fokkers for Horizion - and the 3/5 rule was his lifesaver.  That plane had minimal auto flight capability and absolutely no moving map - just a couple of VOR recieivers and an ADF.  He swore by it.