Simviation Forums

What formula do we use to smoothly descend from high altitude to the destination airport traffic pattern when the terrain between the start of our descent and the final altitude level has mountains enroute?  

I realize there is a formula used; but when I calculate based on its numbers I'll crash into mountains before arrival to the destination airport if I don't readjust my altitude descent rate.  Thanks to all that reply  :)

the MEA is usually listed on the chart and you'd use that altitude as a reference. That combined with the known distance to the mountains + distance to airport will be used to calculate ToD and RoD

To determine ToD: Divide the altitude that must be lost by one thousand, then multiply by 3:
25000/1000 =25 x 3=75nm
Also add 5nm for deceleration below 10.000ft/FL100

Initial RoD:
Groundspeed divided by 2, add a zero and 10%.
440kts/2= 220
Add the Zero= 2200
Add 10%= 2400 ft/min (2420 to be exact)

Keep in mind though that you have to continually reduce the RoD in the lower atmosphere because TAS is slowing but CAS remains constant  :)

I think you need to adjust your starting altitude to take into account the altitude of the destination airport.  For example if the destination is at 4000ft ASL and your cruise altitude is 30,000ft you need to calculate as if you are cruising at (30,000 - 4000) 26,000 feet.

If there are mountains in the way you need to either plot a course around them or pass over them at a safe altitude and then descend on a back course to the airport.

Will

File IFR then follow FS9 ATC instructions.
Bill

None of the replies so far address the possibility that you might be VFR. Under IFR, you should be following published approach procedures which take terrain into account (and under ATC control, which means they'd remind you of area MEAs), so it seems to me you must be talking VFR. Might help to specify...
Assuming you are VFR, you need to either pass over the mountains and double back where you know you can make a normal descent to the pattern without hitting anything, or maybe change course somewhere earlier on to "hook around" some high terrain.
And when it comes to descent from cruise, there's no reason you can't descend, level off for a while, then continue your descent.

VFR was my plan of attack  :)  I know that IFR will tell me everything I need to know to get to the airport and hopefully land safely through my own pilot skill(s), developed by my determination to master my flight simulators [FS2002 / FS2004 / CFS2 / CFS3].  :P

sir_knight, I have the problem quite often, since I quite like flying through mountainous areas - and I prefer not to depend on the autopilot too much.

There's no foolproof method on FS2004, because neither the Map View nor the 'Terrain' setting on the GPS give you spot heights or contours.  In real life, you'd be carrying an old-fashioned map giving you those!  However, luckily, for obvious reasons, almost all airfields in mountanous areas have ILS.

If you're like me, and prefer to keep things 'realistic' (i.e. avoiding flying risks you couldn't afford to take in real life) I reckon that the best way is to stay high till you get your landing clearance, then set up the ILS.  Even flying VFR you can still use it (particularly the glideslope indicator) to prevent any risk of going below minimum height on the approach.

If there's no ILS at a given airport, the ONLY way is to fly a full visual approach from a long way out, avoiding any mountains by flying over or round them!