Descent on final?

[alb469]

We have been experimenting to find an average that works with most A/C. But no consensus seems to work out. How high AGL and how far out out should you be when you start the final descent. Using airports below 5000 ft. Just wondering if anyone has found a happy medium?

[GA_Pilot]

Depends on the aircraft, altittude, and speed, and airport altittude.....For smaller GA aircraft I usually descend in the 500-700 fpm range, for larger jets you can descend faster  

[beaky]

It does depend on the aircraft, but there are two ways to figure this out...
First way: do the math. You should know how many feet from your pattern or cruise altitude you need to lose to reach the runway (your altitude minus the airport elevation), how many feet per minute you're descending (as shown by the VSI), and how many horizontal miles you're covering per minute while descending (groundspeed), so it's not that complicated. Divide the altitude you need to lose by the number of fpm you are descending, then multiply that number by the number of miles per minute. For example:
You want to go straight-in from 3000 feet to a 500-foot elevation runway. Let's say your airplane's nominal approach configuration puts you at 500 fpm with 80 knots indicated...
You need to lose 2500 feet, and the airplane will need 5 minutes to do that at 500fpm. Your airspeed is 80 knots (works for an estimate, but of course wind will reduce your actual groundspeed); that's 1.3 miles per minute (80 divided by 60)... so  if you want to go from 3000 to 500 at 500fpm and 80 kts, you have to start 6.5 nautical miles out (1.3 X 5 =6.5). All of these numbers will of course vary depending on the airplane, wind, etc., etc.
It should be noted that for my RL (light piston) flights, this is precisely how (before I fly) I figure out where to start descending to enter the pattern at the right spot. I work it backwards to figure out where I'll reach the top of climb after takeoff.  Even without factoring in the wind, this method works pretty well in RL and the sim.
Second way(easier, sort of, but more time-consuming): fly an aproach to a runway with ILS or VASI/PAPI. You can determine your distance from the runway at the moment you hit the glideslope at your desired altitude by using GPS, DME, or if at an uncontrolled airport, selecting "report position" from the ATC list. This doesn't help you much with planning descents from different altitudes, unless you figure out the ratio of horizontal feet to vertical feet then apply that to all situations.... but if you have no idea what airspeed/vertical speed you're supposed to have, this'll tell you.
 Of course, if the runway's in sight, even without glideslope and performance information, all you have to do is descend in such a way that the runway doesn't move up or down in your field of vision- it should just get bigger. If it looks like you started decending too far out, just climb a little and try again. If you're too close and the runway's slipping under the nose, go around and try again.

[beaky]

We have been experimenting to find an average that works with most A/C. But no consensus seems to work out. How high AGL and how far out out should you be when you start the final descent. Using airports below 5000 ft. Just wondering if anyone has found a happy medium?

I just realized I gave you the long answer... sounds like you're just asking what the traffic pattern altitude should normally be, right?
In that case:
for light aircraft: 800-1000 AGL
for heavies or fast airplanes that fly a wider pattern: 1200-1500 AGL.
This will vary depending on obstructions, etc., but that's the rule of thumb I use.
 I also use (for flights in the USA) real published TPAs, found in the Airport Facilities Directory, which contains tons of other useful information  about each airport.

[Moach]

i found a "happy medium" that has suited me fine on most aircraft...

as a rule of thumb add 3 miles to your descent to each 1000ft

for instance: if you're flying at 10000ft start your descent 30 miles from the airport, if you're at 20000ft then start at 60 miles out and so on...

then its just a matter of small corrections untill you enter the traffic patern (as for that, the heavier and faster the plane, the longer the approach )


Moach

[Nav]

2,500 feet at 10 miles out is a pretty good starting point. Then keep the nose trimmed level and remember to use power, not pitch, to keep the rate of descent in the 500 feet/minute area.

[MIKE JG]

300 ft. per nautical mile works for just about every aircraft type out there, real and simulated...


So at 1000 feet AGL you should be roughly 3 miles from the threshold.

This approximates a 3 degree glideslope so it works for shooting ILS's and visual approaches.

[alb469]

Thanks all,your answers give a lot of food for thought. We are using a mix of a/c the Dash 7 stol,Convair 990 and F86. The drawback with these is their fairly low stall speeds compared to more modern air liners. Yes I agree that at 3 miles out and 1000 ft agl makes for good landings,{for me most of the time} What we are trying to find now is a good average point to start the final descent. At present we are trying 2200 ft agl and 9 to 10 miles out but that will probably change. Again trying to stay above stall speed and flaring just above the button. Another thing we are trying to figure out is how much above stall speed you should be.  I have flown with some old WW2 pilots and I never knew we were down until you could hear the wheel rumble. Knew one who could make perfect 3 point  landings with a DC3. I should ever be that good!

[Nav]

alb469, why do you feel that the stalling speed of an aircraft is relevant to where you start the descent, and how you land?

At present we are trying 2200 ft agl and 9 to 10 miles out but that will probably change. Again trying to stay above stall speed and flaring just above the button.

It sounds as if you have got the wrong idea about landing altogether - and are maybe trying more or less to 'aim it at the runway' in a dive, hoping to arrive roughly in the right place, rather than flying a proper controlled approach?

If you are having problems landing it might be best to say what those problems are - they are unlikely to be connected with your height and distance out when you start the approach. Any of us would be happy to help but we need guidance as to what the problem is.

You might try Rod Machado's flying lesson on landing too - and have a look at this:-

http://www.simviation.com/cgi-bin/yabb/YaBB.cgi?board=COF;action=display;num=1111322151

[alb469]

Thanks NAV that is an excellent tutorial! Its not that I am having problems landing but most of my flying is done into shorter runways with no VOR/ILS we are just trying to get an average set of procedures I am comfortable with. As for the stall speed, you dont want to go in to fast on a short runway or the obvious will happen. Also we using the keyboard, cant find a stick that I like. We are using your visual perspectives already. When we do use the VOR/ILS system you can be sure we will brush up before with that tutorial.  :)

[Nav]

Thanks, alb469 - that explains the problem. I'd suggest that you tackle things the other way round.