When should I begin my Decent?

[chemgeek]

4 miles per thousand feet you need to lose will work in most low power single engine aircraft with a 500 fpm descent. Keep it simple.

 

[gismo]

4 miles per thousand feet you need to lose will work in most low power single engine aircraft with a 500 fpm descent. Keep it simple.

This really depends on your groundspeed. 4nm per 1000 probably works well with your Grumman but I'm often descending at 200 KTAS or more and with a decent tailwind I can cover 8nm per 1000 ft at 500 FPM.

 

[Ghery]

Interesting, so you are below pattern altitude in a low wing (assuming 1000 AGL) coming into the pattern. I'll have to think about that. It makes some sense.

Some patterns are published as 800 AGL. Check the A/FD.

I personally recommend learning to descend at ~650 fpm; this is the typical ILS/GPS glideslope.

Depends on your approach speed. 90 KTS ground speed and just under 500 fpm will work better.

 

[ja_user]

I find timing to be easier distance. 500 feet per Minute, how high above the pattern are you? That will tell you how many Minutes out to start a normal decent. As Bruce outlined, you may wish to start a little earlier, but this will get you to a pretty good spot.

 

[flyingcheesehead]

I add 10 knots to my GPS-indicated groundspeed to estimate my descent speed (I don't change power right away, just trim forward a bit), divide by 60 and round to the nearest 1/4 mile per minute. 150 knots = 2.5 miles/min, 205 knots = 3.25 miles/min, etc. Subtract the destination field altitude from my cruising altitude and divide by 500 ft/min to get time to descent, then multiply that by the groundspeed in miles per minute as described above.

Yes, I like doing math in my head. But you can use the same method to come up with rules of thumb on the ground - For example, the 4 miles per thousand feet brought up by some others for typical trainers like the C172. (120 knots GS = 2 nm/min at 500 ft/min = 4 nm/1000'.) But when you know where the rule of thumb comes from, you can recalculate it when you move up to higher-performance aircraft.

Unless told by the tower "cleared to land" you are not shooting for the runway, but pattern altitude.

Doesn't really matter - If you shoot for the runway, you'll hit pattern altitude 3-4 miles out from the airport at groundspeeds typical of trainers (I'd hit TPA around 6 miles out in the Mooney, but that still works fine), at which point you can either level off and join the pattern, or continue the approach to the runway as the situation warrants.

You can also approach from any altitude above most airports with a spiraling descent down to pattern altitude, or with clearance, all the way in.

That sounds like a bad idea to me. You'll end up descending right through the pattern, greatly increasing the chance of a midair if there's someone else in the pattern. For traffic avoidance, it'd better to arrive at pattern altitude early so you can get a visual on the other traffic.

Feet in thousands you want to lose (4..5..10.. whatever) x 3 = miles out.

Half your groundspeed, then add a zero and that is your vertical descent rate.

That doesn't work so well for faster aircraft - I'd have to descend at 900-1200 fpm in the Mooney. I prefer to keep it to 500 fpm to be nice to the pax.

I personally recommend learning to descend at ~650 fpm; this is the typical ILS/GPS glideslope.

At Baron speeds, yes. Like the "miles per thousand feet" methods, this depends on your groundspeed. At 90 kts GS, the typical 3-degree glideslope is about 480 fpm.

Some day you may fly high-performance and/or retractable gear aircraft; learning to control airspeed during decent is an important skill in order to stay ahead of the airplane. The best way to do this is to fly by the numbers; start early and you’ll have no issue with transitioning.

Definitely.

 

[Skyscraper]

Forgive the noob question here, but do most of you use trim to get your rate of descent achieved as opposed to using the yoke?

 

[bnt83]

Forgive the noob question here, but do most of you use trim to get your rate of descent achieved as opposed to using the yoke?

Trim if in a hurry, or I back the throttle off very slowly about 200-300 RPM (for fixed pitch props) or a few inches a manifold pressure (for constant speed props)

Or I do a combination of both.

The beauty of using power is, just restore to previous power setting and the airplane levels out by itself no trimming required. Tho you can accomplish the same via trim, just note where the trim was set prior to decent.

 

[douglas393]

Forgive the noob question here, but do most of you use trim to get your rate of descent achieved as opposed to using the yoke?

I pull back power, and rarely touch the trim much, and almost never use the yoke. As you get familar with the flying characteristics of your plane you find the settings that work the best to acheive the speeds and rates you desire.

 

[Skyscraper]

I pull back power, and rarely touch the trim much, and almost never use the yoke. As you get familar with the flying characteristics of your plane you find the settings that work the best to acheive the speeds and rates you desire.

I rarely use the trim either. Mostly I'll use the yoke and throttle together. If using only the throttle, how would you then confirm your exact rate of descent? I'm sure feel and experience is all you really need for most situations, but if you really wanted to hone in one exactly 480 FPM of descent, wouldn't you need to use the yoke, as the adjusting the power doesn't necessarily adjust pitch attitude?

 

[JoeSelch]

I rarely use the trim either. Mostly I'll use the yoke and throttle together. If using only the throttle, how would you then confirm your exact rate of descent? I'm sure feel and experience is all you really need for most situations, but if you really wanted to hone in one exactly 480 FPM of descent, wouldn't you need to use the yoke, as the adjusting the power doesn't necessarily adjust pitch attitude?

Add or remove power without touching the yoke or trim ... the aircraft will adjust its pitch to maintain a constant airspeed.
As for knowing the exact rate of descent, check the VSI (if so equipped).

Try playing around changing only one variable at a time - pitch or power - and see what happens. Get to know your plane.


For me, I tend to use only power for descent from cruise. Pull back 200 RPM or thereabouts for a 500fpm descent in most typical trainers.

 

[douglas393]

I rarely use the trim either. Mostly I'll use the yoke and throttle together. If using only the throttle, how would you then confirm your exact rate of descent? I'm sure feel and experience is all you really need for most situations, but if you really wanted to hone in one exactly 480 FPM of descent, wouldn't you need to use the yoke, as the adjusting the power doesn't necessarily adjust pitch attitude?

480 fpm, sorry I am not that good. I aim for about 500 fpm and just by adjusting the throttle I can acheive that regularly.

 

[RV10flyer]

I dial in my "descend to" altitude and 500 fpm into my EFIS and monitor the magic.

 

[douglas393]

I dial in my "descend to" altitude and 500 fpm into my EFIS and monitor the magic.

Still not 480 fpm:wink2:

 

[Skyscraper]

Add or remove power without touching the yoke or trim ... the aircraft will adjust its pitch to maintain a constant airspeed.
As for knowing the exact rate of descent, check the VSI (if so equipped).

Try playing around changing only one variable at a time - pitch or power - and see what happens. Get to know your plane.


For me, I tend to use only power for descent from cruise. Pull back 200 RPM or thereabouts for a 500fpm descent in most typical trainers.

Thanks for the advice!

 

[MAKG1]

That won't generalize to a high performance aircraft.

There, you can't screw with the throttle too much -- 2 or 3 inches MP all at once is a bit much; much more than that is a big no-no.

But you can nose the aircraft over and descend at 500 FPM or Vno (whichever is the more gradual descent), and gradually reduce throttle to get both at once, and keep it there.

There is no reason to descend at any airspeed below Vno unless it's turbulent (then, use Va). The guy behind you inbound will appreciate that. So will the Hobbs meter.

 

[comanchepilot]

This is so easy and does not matter one whit if you are at 400 knots or 40 . . .

Time to Airport times two, drop the zeros. 500fpm.

If you want to go down at 1000fpm, then its time to destination, drop the zeros.

Are you 6000 feet? Pattern Alt is 1500? Need to lost 4500 feet to pattern altitude? 45, times 2 = 90 - drop the zeros - 9 min out. 500 fpm. should put in 2-3 miles out since you slow down as you descend generally.

Are you 16,000 feet, in a jet, at 400kts about 10k and 250 below? And need 1000fom? 16000 / 1000 = 16 min out. You will need to slow at 10k, but you will also need to slow to deploy things like flaps and gear. It all works out. No one in a jet ever descends that way anyway - even at 4am.

If you are piston IFR none of this is important since you get told when to descend and to what altitude - unless you are in a part of the nation where you can ask for a PD.

 

[John Baker]

That sounds like a bad idea to me. You'll end up descending right through the pattern, greatly increasing the chance of a midair if there's someone else in the pattern. For traffic avoidance, it'd better to arrive at pattern altitude early so you can get a visual on the other traffic..

You are right, I did not explain that properly. I've done the spiraling descent more than a few times at both Ramona, but especially over the hill at Borrego Valley.

I should have explained that it is never done directly above the pattern, but well off to the side of it, over a field or like Borrego, empty desert.

Join the pattern in the normal manner at 45 to the downwind unless otherwise instructed.

-John

 

[taters]

I triple the altitude to lose ie 5 thousand equals is 15 miles out
Add a zero to the ground speed /2 and that's your decent rate 100(0) knots/2 500 FPM.

 

[keo56]

Amount of altitude you need to lose, double it, thats how far from destination you should start a standard rate of descent. (If you are a fast mover add 15 to the number)

Example: At 12,000 ft, pattern alt at destination is 1K, need to lose 11K....double 11 = 22 mile out start a standard rate. Always work for me. Taught to me by a grey-beard pilot, may god hold him close.

 

[denverpilot]

My airplane is slow, so I just trim down, and keep trimming down until the airspeed barely makes it to yellow line. Sometimes. Just pick a reasonable rate of descent for human ears.

Throttle stays wide open. I'd like to arrive before next Thursday. Haha.

Throttle doesn't come back until level off at pattern altitude -- in time to slow up to enter the pattern at or slightly above and slowing to, a reasonable pattern speed.

The 182 is nothing but drag, so that doesn't take very long.

That's VFR of course... IFR it's slowed up for the approach before the FAF to a speed I and the controller can live with.

So there's not a good answer for the question that covers every airplane and all scenarios.

Kent even has speed brakes, but I know he tries not to use them. Waste of energy.

Like the old joke...

"Airliner 1234 cross INT at or below one-zero thousand, reduce speed to 210 knots."

"Unable, Airliner 1234"

"Doesn't that thing have speed brakes?"

"Yeah, but they're for my mistakes, not yours."

 

[flyingcheesehead]

Amount of altitude you need to lose, double it, thats how far from destination you should start a standard rate of descent. (If you are a fast mover add 15 to the number)

Example: At 12,000 ft, pattern alt at destination is 1K, need to lose 11K....double 11 = 22 mile out start a standard rate. Always work for me.

You must fly a pretty slow airplane... To get a 500 fpm descent using that method, you'd have to be going only 60 knots. If I tried that using a normal descent in the Mooney, I'd have to make the entire descent at an ear-popping 1500 fpm!

Also, what do you consider a "standard rate of descent"?

 

[azure]

Amount of altitude you need to lose, double it, thats how far from destination you should start a standard rate of descent. (If you are a fast mover add 15 to the number)

Don't double it, multiply by your ground speed in kts, mod 30. I use the next higher multiple of 30. So if I'm going 110 kts I multiply by 4, but if I'm going 130 kts, I multiply by 5. In your example, at 130 kts I would need 55 nm to descend at standard rate to pattern altitude.

 

[EdFred]

$10,000 answers to a $5 question.

 

[EdFred]

Actually, a jet will fly the same decent gradient as any other plane. It is a requirement. This is important to know for wake turbulence avoidance.

Meh. I generally see all white on the PAPI/VASI until I am SHORT final. I pretty sure the jets don't come in as high as I do. My power off descent isn't 3 degrees.

 

[denverpilot]

Meh. I generally see all white on the PAPI/VASI until I am SHORT final. I pretty sure the jets don't come in as high as I do. My power off descent isn't 3 degrees.

I've had at least one person say that a steep power-off descent wasn't "stabilized". Which, of course, is rediculousness...

But it shows the misconception and inaccurate conmection some make between "stabilized approach" and "standard glidepath angle".

I need to be WAY above the VASI or PAPI or what-have-you... to make a stabilized power-off approach with the flaps hanging out at 40 degrees. At least one advocate of "stabilized approaches" didn't like a trimmed, hands-off, steep power off descent at Flaps 40 in the 182 and thought it "wasn't stabilized".

 

[MAKG1]

That's odd. It's stabilized if the airspeed, vertical speed, course and configuration are constant. Regardless of how steep the glidepath is.

That it's not on the PAPI's glidepath but on some other is an orthogonal question.

It makes me wonder....under such logic, is there a such thing as a stabilized approach with no visual glidepath references?

I've certainly made my share of steep stabilized approaches. Sometimes you need to due to terrain, for instance. Like landing at 2O3 on rwy 34 (there is a ridge ahead of short final).

 

[EdFred]

That's odd. It's stabilized if the airspeed, vertical speed, course and configuration are constant. Regardless of how steep the glidepath is.

That it's not on the PAPI's glidepath but on some other is an orthogonal question.

It makes me wonder....under such logic, is there a such thing as a stabilized approach with no visual glidepath references?

I've certainly made my share of steep stabilized approaches. Sometimes you need to due to terrain, for instance. Like landing at 2O3 on rwy 34 (there is a ridge ahead of short final).

If the runway numbers ain't moving up and down on the windscreen, and I'm not constantly jacking with the power to keep them still, I call it stabilized. That's my visual reference.