# Wonder if App is... Applicable

Maybe this belongs in games, but I’m looking for opinions and this might be useful in real world general aviation (doubtful) so in IMHO it goes. Mods, please move it as you see fit.

About once a year I get a bee in my bonnet to fire up MS Flight Simulator. I find that I spend quite a bit of time figuring out the proper approach for a landing at any particular airport. So… I wrote a simple Android App for use in calculating some basic numbers.

The basic numbers being -

Ground speed - (airspeed won’t work)
Altitude to lose - (you’re at 12,000, the airport is a 2000, so you need to lose 10000)
Feet per minute - (how fast you descend)
Commit point - (NM from the airport. Basically when you pull the trigger.)

Key in any three of those numbers, and the app calculates the forth. Kinda handy for an idea of what needs to be done.

I’m sure that this info is already in every flight plan (or should be), but perhaps having a simple calculator like this would be handy. What say you SDMB?

I’m pretty sure those calculations are already available in some flying apps. To be honest I think that it is of perhaps academic interest to flight simmers but not of much use in the real world as basic rules of thumb are quicker and good enough to get a good result.

For a pressurised aircraft (descent rate is not restricted by passenger comfort) use the following.

Commit point in NM = altitude to lose in 1000’s of feet * 3
Required vertical speed = 5* ground speed plus a bit (about 7-10%).

10,000’ to lose = top of descent at 30 NM
Ground speed 300 knots = 1600 fpm vertical speed required.

The problem with doing one precise calculation is that ground speed changes during the descent as true airspeed and wind speed reduce with decreasing altitude. If you can do it with quick mental sums you can adjust things on the go depending on how your descent plan is going.

There are similar rules of thumb for unpressurised aircraft that are essentially restricted to 500 fpm rate of descent for passenger comfort but I can’t remember them.

So by all means make it into an app, make it look nice and charge a couple of bucks for it and someone will purchase it, but keep in mind your target audience is flight simmers rather than real world pilots.