I'm lazy so I don't do all those calculations.

At FL300 start a descent 100 miles from the airport. Reduce airspeed to 200 kia and set the AP to 3-5000 ft., depending on the airport altitude.  Since you are descending your airspeed will not go to 200 kia but will remain about 275-300 kia.  When you reach your desired altitude lower your speed and extend your flaps and gear for landing.

8)
Oh a very nice subject indeed, and quite frankly I won't be able to give you any easy answers.
The 737 can descend in many ways by using the autopilot, but only 1 of them is modelled in the stock 737's: the vertical speed mode.
By using the V/S thumbwheel you can select a RoD (rate of Descent) that will maintain a constant angle. Throttles are not at full idle, we're conducting a partial throttle descent here.
First let's assume your descent speed will be around m.76/300
I noted you were already aware of the 3:1 method to determine how far away from the airport you should start your descent....for the 737 add an extra of 5nm to slow from 300 to 250kts when passing 10.000ft. That should be fine.

So you know which technique to use (V/S) and how far away you will begin to descent...now we only need to find out what your initial Vertical speed will be.

Take your groundspeed, divide it by 2 and add a zero and 10%.
So if you have a GS of 440kts, half of that is 220...add 10% (12) =240
Add the zero= 2400

Your rate of descent will be 2400ft/min...but then you got to let speed bleed off at 10.000ft. This is in general 35nm from the airport. At 250kts  V/S will decrease to maybe 1200ft/min. Remember you can't sink too steep or else you will bust the flap extend speeds
When you reach the outer marker a 750ft/min descent at 140kts is enough to maintain the 3 degree slope

Then we have the idle throttle descent...in real life conducted in the VNAV or LVL CHG mode of the autopilot. The FMC will calculate a Top of Descent point where the aircraft will start a power-off glide to the next waypoint containing an altitude restriction. Disadvantages here is that the descent can be very steep and very little room is given to meet speed restrictions from ATC (and in crowded airspace that is very very likely to happen)...also the cabin altitude rate of change is faster which can cause the funny feeling in your ears

Interesting note: There is no significant fuel savings between idle and partial throttle descents.

I hope this makes sense

Slightly aside from but related to Silver's response, in the real world ALL heavy flights are IFR including approaches, this regardless of meterological conditions.

Procedures vary, but AA's calls for controlled arrivals along preplanned routes and precision approaches (autopilot) to DA.

BTW, I am not an airline pilot and did not sleep in a Holiday Inn Express...but I pester and live vicariously through such people.

The Dragonfighter

This and other FS9 answers are included in the program. Using Windows Explorer (if not using  in FS9's F10 key --kneeboard) open FlightSimulator 9/FSWeb/Learning Center/B747/FlightNotes. Everything is there.
Enjoy,
Bill
here's the link to the file:///C:/Program%20Files/Microsoft%20Games/Flight%20Simulator%209/FSweb/Learni... link but it may not display properly here

No problem Juanca, that's what this forum is all about 

hey Pal..I recreated your scenario with the default 737-400.
At 24.000ft, I had an IAS of 290 (Groundspeed 424kts)

By using the formula above, my vertical speed should be around 2300

I managed it to work very well (nice work MS programmers )

even though I was VERY heavy (95%fuel left) I flew it without autothrottle, LP compressor (N1) at around 40%, had no problems with keeping the airspeed, even down to 10.000ft where I decel to 240kts...

Here's a screenie
:

Don't know why it didn't work for you?