Staying on glideslope.

[Mistake Not...]

I know this must have been asked an answered a billion times. I've even found magazine articles on it, but it seems like none of them actually answer the question "What's the best technique for staying on glideslope". Oh sure, they'll have that as the title, then it's all "keep your scan up and keep the needles crossed". Well. Duh.

So, previous instructor wanted a constant airspeed and a preselected descent rate interpolated (quick guess) required to maintain a 3deg slope based on ground speed reported by GPS. That is, look at ground speed, realize you need 478ft/min at 90kts, guess, then adjust power once starting down to maintain both 90kts and keep the needles centered.

Talking to more people since then, a common technique seems to be: Go to preselected power settings, hold glideslope with pitch.

I've tried both, and in the mooney and a sim, and the second is just WAAAAAAY easier for me at my current level of ability. And, it's what the autopilot would have to do, since I don't have a throttle servo. So.. is it a bad technique, and why the complicated one from the instructor?

 

[gsengle]

Well I do both. I do number 2. I start with known settings and config that work. If I'm noticibly fast or slow as I do it I adjust power.


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[Mistake Not...]

Well I do both. I do number 2. I start with known settings and config that work. If I'm noticibly fast or slow as I do it I adjust power.


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Yeah, and that makes sense. My instructor wanted 90kts regardless. If you go by ACS, you get +/- 10kts. Which, unless you're in a hurricane, should be enough margin to compensate for reasonable head wind.

Also, pitch is much quicker to respond than power. But his thing was "pitch to your airspeed, power to your rate", so I ended up constantly adjusting throttle (probably my bad, but...).

 

[Chip Sylverne]

I try fly by the numbers. Not only is it easier to maintain a constant descent rate, but should you lose your asi, you know what rpm, mp and pitch yield a given airspeed. Fr'instance, in my airplane, 18", 2400 rpm in level flight gives me 120kts. Reducing mp to 15" will give me a 500' fpm descent same speed without changing a thing. Keeping 18" and dropping the gear at the FAF gives the same descent rate. Makes GS tracking easier. I should also add I fly my approaches at 120kts. Bumps me up a category, but the airplane is much more solid and does away with any timing interpolation.

Now on a non-precision "dive and drive", depending on what the ceilings are and how far I am from the Maltese cross, I might expedite the descent to get under the deck as soon as safely possible.

 

[labbadabba]

I go with a combo. I set my power for a typical 90 knot descent and then I look at my VSI and Ground Speed. On a 3-degree glide slope, I know that flying 60 knots is 318fpm, 90 knots is 478, and 120 knots is 637. So based upon what performance I'm getting I'll interpolate those numbers and try to peg my VSI and cross check against the GS needle.

 

[dmspilot]

I know this must have been asked an answered a billion times. I've even found magazine articles on it, but it seems like none of them actually answer the question "What's the best technique for staying on glideslope". Oh sure, they'll have that as the title, then it's all "keep your scan up and keep the needles crossed". Well. Duh.

So, previous instructor wanted a constant airspeed and a preselected descent rate interpolated (quick guess) required to maintain a 3deg slope based on ground speed reported by GPS. That is, look at ground speed, realize you need 478ft/min at 90kts, guess, then adjust power once starting down to maintain both 90kts and keep the needles centered.

Talking to more people since then, a common technique seems to be: Go to preselected power settings, hold glideslope with pitch.

I've tried both, and in the mooney and a sim, and the second is just WAAAAAAY easier for me at my current level of ability. And, it's what the autopilot would have to do, since I don't have a throttle servo. So.. is it a bad technique, and why the complicated one from the instructor?

The second technique is more common and is recommended by ASA's Instrument Flying book and by Barry Schiff in Proficient Pilot, among others I'm sure. However I am a little bit confused about what exactly the first technique is. Are you saying you pitch down and only adjust the power afterward to compensate for the increased speed?

 

[labbadabba]

But his thing was "pitch to your airspeed, power to your rate", so I ended up constantly adjusting throttle (probably my bad, but...).

Really?? That to me is weird. My instructor who taught me to fly the VSI told me just the opposite. When flying a visual approach he says, pitch for airspeed/power for altitude. When flying a constant rate, you power for airspeed/pitch for rate. That to me makes sense. Since you're well above the power curve you don't need to fly in the region of reverse command.

 

[Mistake Not...]

The second technique is more common and is recommended by ASA's Instrument Flying book and by Barry Schiff in Proficient Pilot, among others I'm sure. However I am a little bit confused about what exactly the first technique is. Are you saying you pitch down and only adjust the power afterward to compensate for the increased speed?

Yup. Say you're 95kts. Pitch up to slow down, but now your vertical speed is lower, so pull some power off too. I find it very difficult to do at this stage in my training. Lots of things going on all at once. I asked multiple times why do it this way, and got "The examiner wants to see a stabilized approach."

 

[Mistake Not...]

Really?? That to me is weird. My instructor who taught me to fly the VSI told me just the opposite. When flying a visual approach he says, pitch for airspeed/power for altitude. When flying a constant rate, you power for airspeed/pitch for rate. That to me makes sense. Since you're well above the power curve you don't need to fly in the region of reverse command.

Heh. I had to read that multiple times before what I -thought- you were saying stopped getting in the way of what you actually wrote.

So, your instructor's way, if I wanted 450ft/min, I'd pitch for that, and then adjust throttle to get my 90kts? (Since they're both related, I guess it's just a question of which one to hold constant. What I like about yours, if I had to do it, is that the RATE is more important for staying on glide slope than air speed.)

 

[Mistake Not...]

I try fly by the numbers. Not only is it easier to maintain a constant descent rate, but should you lose your asi, you know what rpm, mp and pitch yield a given airspeed. Fr'instance, in my airplane, 18", 2400 rpm in level flight gives me 120kts. Reducing mp to 15" will give me a 500' fpm descent same speed without changing a thing. Keeping 18" and dropping the gear at the FAF gives the same descent rate. Makes GS tracking easier. I should also add I fly my approaches at 120kts. Bumps me up a category, but the airplane is much more solid and does away with any timing interpolation.

Now on a non-precision "dive and drive", depending on what the ceilings are and how far I am from the Maltese cross, I might expedite the descent to get under the deck as soon as safely possible.

Take your example (I have similar numbers figured out for the mooney).. You set the airplane up for those power settings and get 500fpm. Do you then adjust power to stay on glide slope, or just use pitch? Obviously, the same numbers only work with a certain headwind. If that changes, I don't see how the numbers work anymore UNLESS pitch is used to hold glideslope, and you take whatever variation in IAS that gives you.

 

[Bill]

In my 201, I trim for 90kts clean before the glide slope intercept. I know that if I'm on 90 and trimmed, lowering the gear and putting in takeoff flaps will have her going down the pipe at 90kts +/- a few. May need a skitch of throttle in or out to maintain 90kts, but only a skitch. From there pitch for glide slope.

 

[Larry in TN]

Pitch for G/S. Works in anything from a C-172 to a B767.

 

[Mistake Not...]

Thanks, y'all. It's nice to have some confirmation. Maybe there's a reason he wanted it done his way, but there's an easier way (pitch for glideslope) and it's legal and safe.

Stuff like this is what has run the number of instruction hours up above what I see everyone else reporting for an instrument rating, and no end in sight. I fired the instructor, and PIC is coming in March.

 

[coloradobluesky]

Do it the same way every time. Know the throttle settings and all the other engine and airframe settings to get your descent and airspeed at target. You will usually have to make some adjustments, but not many. Fly the same approach 10 times the same way every time. Now you have the confidence to do it in actual. So do it in actual. Fly to minimums if you can get them.

 

[mscard88]

I use and teach using something like this chart. Use it for a crutch to start with and then after awhile you'll have everything more or less memorized.

 

[FastEddieB]

Pitch for G/S. Works in anything from a C-172 to a B767.

Since that's how autopilots do it, it must work!

And if equipped, autothrottles control airspeed.

 

[Chip Sylverne]

Take your example (I have similar numbers figured out for the mooney).. You set the airplane up for those power settings and get 500fpm. Do you then adjust power to stay on glide slope, or just use pitch? Obviously, the same numbers only work with a certain headwind. If that changes, I don't see how the numbers work anymore UNLESS pitch is used to hold glideslope, and you take whatever variation in IAS that gives you.

Once set up, minor g/s adjustments I make with pitch. But I don't understand your comments on winds. Once set up with power and pitch, the airplane will fly at the same IAS in that configuration no matter what the winds are. Your speed over the ground will change, it may take you longer to come down the GS, but the airplane will fly the same in a given configuration every time.

 

[aterpster]

Pitch for G/S. Works in anything from a C-172 to a B767.

Even to the A380 Larry.

 

[Everskyward]

Take your example (I have similar numbers figured out for the mooney).. You set the airplane up for those power settings and get 500fpm. Do you then adjust power to stay on glide slope, or just use pitch? Obviously, the same numbers only work with a certain headwind. If that changes, I don't see how the numbers work anymore UNLESS pitch is used to hold glideslope, and you take whatever variation in IAS that gives you.

Once set up, minor g/s adjustments I make with pitch. But I don't understand your comments on winds. Once set up with power and pitch, the airplane will fly at the same IAS in that configuration no matter what the winds are. Your speed over the ground will change, it may take you longer to come down the GS, but the airplane will fly the same in a given configuration every time.

The airplane will fly at the same IAS with a strong head or tailwind, but you won't stay on the glideslope unless you adjust your rate of descent or your groundspeed. There is a rule of thumb for a 3 degree rate of descent. It is groundspeed X 5. So if you are flying at 100 knots, your rate of descent should be about 500 fpm to stay on the glideslope, using @Mistake Not... 's example above. However the same airplane with a 50 knot headwind (exaggerating for math purposes) will only need a 250 fpm rate of descent. So in that instance, you would shallow your descent to 250 fpm which uses more power. You could also increase your groundspeed back to 100 knots and use a 500 fpm rate of descent, but that would also use more power and might make the landing a little more challenging!

It's great to have a power setting in mind when flying a glideslope, but that power setting may need to be tweaked depending on the winds. In general, you will need more power in a strong headwind.

 

[MAKG1]

Really?? That to me is weird. My instructor who taught me to fly the VSI told me just the opposite. When flying a visual approach he says, pitch for airspeed/power for altitude. When flying a constant rate, you power for airspeed/pitch for rate. That to me makes sense. Since you're well above the power curve you don't need to fly in the region of reverse command.

I've heard -- and tried -- both, and my experience is that I have an easier time adjusting GS with throttle PROVIDED I change no more than 100 RPM or 1 inch Hg at a time. More than that, and you chase needles. It usually comes with a very slight pitch change as well, but not a trim change (unless I deploy flaps or gear). The pitch change is to prevent a transient; without it, the airplane will fly a phugoid around the GS.

The advantage here comes when there is some wind shear on the approach, which is common. I may see 25 knots wind at 3000 and 10 knots at the surface.

The pitch method essentially tries to keep the ground speed constant, which is a good thing (and rather important!) if you're timing an approach, but not so good otherwise, especially with a tailwind.

 

[labbadabba]

Heh. I had to read that multiple times before what I -thought- you were saying stopped getting in the way of what you actually wrote.

So, your instructor's way, if I wanted 450ft/min, I'd pitch for that, and then adjust throttle to get my 90kts? (Since they're both related, I guess it's just a question of which one to hold constant. What I like about yours, if I had to do it, is that the RATE is more important for staying on glide slope than air speed.)

Basically, yeah. You configure for your descent and pitch for 450fpm on the glide slope and adjust your power to get 90kts over the ground. If that really screws with your indicated airspeed then you just interpolate. So let's say you have a 30 kt headwind, instead of jacking around with your power, you just change your pitch to 320 fpm on the descent.

If you can nail your rate of descent for your ground speed you never have to worry about the glide slope needle. That way you aren't constantly chasing the needle, you're more concerned with how you're configured. If you're configured correctly the plane will fly itself down the glide slope.

 

[labbadabba]

I've heard -- and tried -- both, and my experience is that I have an easier time adjusting GS with throttle PROVIDED I change no more than 100 RPM or 1 inch Hg at a time. More than that, and you chase needles. It usually comes with a very slight pitch change as well, but not a trim change (unless I deploy flaps or gear). The pitch change is to prevent a transient; without it, the airplane will fly a phugoid around the GS.

The advantage here comes when there is some wind shear on the approach, which is common. I may see 25 knots wind at 3000 and 10 knots at the surface.

The pitch method essentially tries to keep the ground speed constant, which is a good thing (and rather important!) if you're timing an approach, but not so good otherwise, especially with a tailwind.

I can see that, especially with a tailwind if you're only indicating 60kts to keep 90kts GS. I've found tho, with my own flying that I've been much more stable when I worry about pegging my VSI/rate rather than trying to get my throttle just right for the Glide Slope.

When I can peg a rate for a given airspeed it works basically everytime and I have specific numbers I can shoot for. When I'm adjusting my throttle to meet the glide slope it feels like a much more inexact science.

 

[FastEddieB]

I learned and later taught pitch for glideslope and power for airspeed. The glideslope is so "thin" that small pitch changes seem to work better than adjusting power, which seems to have a delayed effect.

But note that if you're flying with someone who keeps it glued to the glideslope, you will be hard pressed to tell from his actions what is controlling what. In other words, whatever is working for you, keep doing it!

 

[MAKG1]

I can see that, especially with a tailwind if you're only indicating 60kts to keep 90kts GS. I've found tho, with my own flying that I've been much more stable when I worry about pegging my VSI/rate rather than trying to get my throttle just right for the Glide Slope.

When I can peg a rate for a given airspeed it works basically everytime and I have specific numbers I can shoot for. When I'm adjusting my throttle to meet the glide slope it feels like a much more inexact science.

Except the rate is for a given ground speed, not airspeed.

 

[Cooter]

Small GA planes are so pitch responsive, it seems to make pitch/airspeed, power/glideslope more difficult. In the military aircraft I've flown, I use power for glideslope and only "influence" the nose to minimize the delay in response. If you ever have the opportunity to fly with a HUD and velocity vector (or Flight Path Marker), it makes more sense. My technique was to trim it on speed, configured and at GS intercept crack the power, lower the nose 3 deg and give it two clicks of nose down trim. Then once I intercept my target VSI, make adjustments to glideslope with VSI as the reference point. All the while, little to no nose movement at all. I find personally that flying the GS with the nose makes for more sloppy aircraft control. I forgot to add, that airspeed adjustments are made largely by clicks of trim and slightly bumping the nose.

 

[Everskyward]

If you fly with a flight director, either hand flown or coupled to the autopilot, it is pitching to the glideslope...

 

[labbadabba]

Except the rate is for a given ground speed, not airspeed.

Yes, that's what I meant... So if I'm coming into an approach I'll set my descent power, pitch for 475fpm and check my ground speed. If I'm off by a couple knots I'll adjust my power to hit 90 over the ground. If there's a big differential, I'll re-calculate my rate of descent from there.

 

[UngaWunga]

So, your instructor's way, if I wanted 450ft/min, I'd pitch for that, and then adjust throttle to get my 90kts? (Since they're both related, I guess it's just a question of which one to hold constant. What I like about yours, if I had to do it, is that the RATE is more important for staying on glide slope than air speed.)

I've just started training as well, but pitch and airspeed are connected when trying to maintain a specific glideslope. No way around it.
You'll have to change both to get 450'/min decent at 90kts. If you set up for 450', you'll need to pull power back a little to maintain 90. Then you'll need to modify pitch when speed gets back to 90. The goal is to be close. You'll figure out what you need for pitch and power for your plane. You can practice that anywhere, don't need to be on an approach. Go up a few thousand feet somewhere and try it out. When you find a combo that works, make a note of it so you can quickly find it next time.

 

[UngaWunga]

Yes, that's what I meant... So if I'm coming into an approach I'll set my descent power, pitch for 475fpm and check my ground speed. If I'm off by a couple knots I'll adjust my power to hit 90 over the ground. If there's a big differential, I'll re-calculate my rate of descent from there.

Yup.

 

[midlifeflyer]

If you fly with a flight director, either hand flown or coupled to the autopilot, it is pitching to the glideslope...

That is how an autopilot does it. It works for us too. Here's the catch: to work we have to fly like an autopilot. That means seeing deviations early and correcting them with tiny pitch adjustments so that the airspeed variations are tiny as well. Let it get away, or in gusty conditions, a power change will be needed as well, with or without an autopilot (absent autothrottles).

 

[mscard88]

So, no one has mention using the AOA to follow the GS...

 

[GrahamC]

Talking to more people since then, a common technique seems to be: Go to preselected power settings, hold glideslope with pitch.

This.

You cant reasonably fly a small airplane well unless you understand the airplane's pitch and power settings for different phases of flight.
One of the first things I do whenever I get into an airplane I've never flown before is go though a thorough briefing with whichever pilot or instructor I'm flying with on the pitch and power settings for that airplane.
You cant change your pitch without changing your power, and vice versa.
I cringe every time I hear the words Pitch for airspeed, Power for altitude.

 

[MAKG1]

That is how an autopilot does it. It works for us too. Here's the catch: to work we have to fly like an autopilot. That means seeing deviations early and correcting them with tiny pitch adjustments so that the airspeed variations are tiny as well. Let it get away, or ingust conditions, a power change will be needed as well, with or without an autopilot (absent autothrottles).

Well, most of us don't have autothrottles, so an autopilot only has pitch to work with.

 

[labbadabba]

I cringe every time I hear the words Pitch for airspeed, Power for altitude.

I disagree, I think it has its place. Learning how to fly behind the power curve is very useful especially those last few precious seconds after crossing the runway threshold to the flare. When I'm flying a pattern, especially a tight pattern where I don't have a nice long ILS to configure at 90 knots, flying essentially a power-off 180 it's all about pitching for airspeed.

 

[bobmrg]

I know this must have been asked an answered a billion times. I've even found magazine articles on it, but it seems like none of them actually answer the question "What's the best technique for staying on glideslope". Oh sure, they'll have that as the title, then it's all "keep your scan up and keep the needles crossed". Well. Duh.

So, previous instructor wanted a constant airspeed and a preselected descent rate interpolated (quick guess) required to maintain a 3deg slope based on ground speed reported by GPS. That is, look at ground speed, realize you need 478ft/min at 90kts, guess, then adjust power once starting down to maintain both 90kts and keep the needles centered.

Talking to more people since then, a common technique seems to be: Go to preselected power settings, hold glideslope with pitch.

I've tried both, and in the mooney and a sim, and the second is just WAAAAAAY easier for me at my current level of ability. And, it's what the autopilot would have to do, since I don't have a throttle servo. So.. is it a bad technique, and why the complicated one from the instructor?

How does the autopilot do it? Pitch to the glideslope, power to the airspeed (only in your case there is no autothrottle).

Bob

 

[GrahamC]

I disagree, I think it has its place. Learning how to fly behind the power curve is very useful especially those last few precious seconds after crossing the runway threshold to the flare. When I'm flying a pattern, especially a tight pattern where I don't have a nice long ILS to configure at 90 knots, flying essentially a power-off 180 it's all about pitching for airspeed.

You're trying to throw an orange at an apple stand.

When flying to maintain a pre-determined glidepath (the apple stand,) as in the scenario that the OP presented, you cannot change one without having to change the other. Why separate them, instead of making coordinated and combined corrections to maintain your predetermined flight path?

In your scenario, a power off 180, power is a constant (Idle.) In this case (the orange) your only variable left is pitch.

Break.

To your other point, learning to fly behind the power curve is imperative. But try to prove that you can maintain altitude and change your airspeed in slow flight without also changing your power setting.

 

[bobmrg]

So, no one has mention using the AOA to follow the GS...

Please. Enough already.

Bob

 

[dmspilot]

I cringe every time I hear the words Pitch for airspeed, Power for altitude.

Eh, I think it has it's place, like for the single-digit-hour student pilot learning to land who thinks that in order to descend you have to point the nose at the ground.

 

[Larry in TN]

Even to the A380 Larry.

I was commenting from personal experience. I've never flown anything larger than the 767.

 

[GrahamC]

Eh, I think it has it's place, like for the single-digit-hour student pilot learning to land who thinks that in order to descend you have to point the nose at the ground.

This is exactly the place where you would not want to introduce this phrase. Primacy is key.