Stabilized Approach - Glideslope Edition

labbadabba

labbadabba

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labbadabba
So, did my mock checkride with our chief pilot. He's a corporate pilot with 26,000 hours mostly turbine. He gave me a full endorsement so that was good but he did have some interesting pointers, one of which struck me as odd.

Typically to stabilize my decent, I set descent power, pitch for 90KIAS and adjust power based upon my VSI/Glideslope. This is the standard behind the power curve flying just like any VFR pilot would fly.

His suggestion for a 3-degree GS was to pitch for 450fpm on the VSI and set descent power for 90KGS. So in other words, pitch for altitude and power for speed like cruise flight. He said that this method leads to less of a pitching moment when trying to establish the glideslope.

I'll give it a shot, but I wonder if this technique is more suited to flying a jet rather than a 160hp piston.
 
There are many ways to skin a CAT. Nothing prevents you from experimenting, but my own preference is to use the conventional power for VS and pitch for AS. The reason is that I like to be trimmed for AS, so pitch should be pretty much neutral, except to prevent excursions due to turbulence. Using power for VS and Glide Slope tracking works for me because I can make very tiny adjustments and keep it there, like trim. So essentially coming down the GS I have two trimmed vertical inputs: power and pitch trim, which makes the vertical dimension very stabilized, allowing me to focus on the lateral dimension which typically requires more work, esp. closer in.
 
RotorDude said:
There are many ways to skin a CAT. Nothing prevents you from experimenting, but my own preference is to use the conventional power for VS and pitch for AS. The reason is that I like to be trimmed for AS, so pitch should be pretty much neutral, except to prevent excursions due to turbulence. Using power for VS and Glide Slope tracking works for me because I can make very tiny adjustments and keep it there, like trim. So essentially coming down the GS I have two trimmed vertical inputs: power and pitch trim, which makes the vertical dimension very stabilized, allowing me to focus on the lateral dimension which typically requires more work, esp. closer in.
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+2 good explanation Rotor
 
Pitch and power are inter-related for stabilized approach. Best to go back to basics.

Throttle for power.
Elevator for pitch.
 
RotorDude said:
There are many ways to skin a CAT. Nothing prevents you from experimenting, but my own preference is to use the conventional power for VS and pitch for AS. The reason is that I like to be trimmed for AS, so pitch should be pretty much neutral, except to prevent excursions due to turbulence. Using power for VS and Glide Slope tracking works for me because I can make very tiny adjustments and keep it there, like trim. So essentially coming down the GS I have two trimmed vertical inputs: power and pitch trim, which makes the vertical dimension very stabilized, allowing me to focus on the lateral dimension which typically requires more work, esp. closer in.
Click to expand...

Agreed, I like the idea of trimming for an airspeed, provided there's not a drastic change in wind speed/direction, your descent should basically be stable without having to touch the elevator if properly trimmed.

In fairness, he may have meant this as a technique to get established onto the glide slope since ground speed is what will ultimately determine the descent rate on a glide slope. Once established then you can go back to the typical configuration of pitching for airspeed. I'll text him to see if that's what he meant...
 
BigBadLou said:
I see what you did there. :D

If you use GS for reference, now you need to work constantly against the changing wind. If you have 30 on the nose, you'll have to fly the ILS at 120KIAS to maintain GS at 90.
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Either that, or fly the VSI at 300fpm...
 
labbadabba said:
So, did my mock checkride with our chief pilot. He's a corporate pilot with 26,000 hours mostly turbine. He gave me a full endorsement so that was good but he did have some interesting pointers, one of which struck me as odd.

Typically to stabilize my decent, I set descent power, pitch for 90KIAS and adjust power based upon my VSI/Glideslope. This is the standard behind the power curve flying just like any VFR pilot would fly.

His suggestion for a 3-degree GS was to pitch for 450fpm on the VSI and set descent power for 90KGS. So in other words, pitch for altitude and power for speed like cruise flight. He said that this method leads to less of a pitching moment when trying to establish the glideslope.

I'll give it a shot, but I wonder if this technique is more suited to flying a jet rather than a 160hp piston.
Click to expand...

You are not behind the power curve at 90 knots, not even close.

The technique the chief pilot described is the way ILS is usually taught.
 
kgruber said:
Pitch and power are inter-related for stabilized approach. Best to go back to basics.
Click to expand...
That's really the bottom line. And, felines aside, there are multiple way to accomplish it.

For glidepath, for me it depends.

Once the glideslope is captured and descent stabilized on a relatively calm day, I will control the glideslope with pitch. The deviations tend to be minor and correctable with slight pressure on the yoke or stick with only minor changes in airspeed. The throttle, even with a vernier, doesn't seem to have the same degree of "touch and feel." Heck, the autopilot does that and seems to do a great job of tracking.

Of course, that's not the end of the story and one has to be ready to add or reduce power if the excursions are or threaten to be greater. You need to do that with an autopilot too (assuming you don't have one with auto-throttle).
 
BigBadLou said:
I see what you did there. :D

If you use GS for reference, now you need to work constantly against the changing wind. If you have 30 on the nose, you'll have to fly the ILS at 120KIAS to maintain GS at 90.
Click to expand...

I think we are using "GS" to mean "Glide Slope" in this thread.
 
labbadabba said:
So, did my mock checkride with our chief pilot. He's a corporate pilot with 26,000 hours mostly turbine. He gave me a full endorsement so that was good but he did have some interesting pointers, one of which struck me as odd.

Typically to stabilize my decent, I set descent power, pitch for 90KIAS and adjust power based upon my VSI/Glideslope. This is the standard behind the power curve flying just like any VFR pilot would fly.

His suggestion for a 3-degree GS was to pitch for 450fpm on the VSI and set descent power for 90KGS. So in other words, pitch for altitude and power for speed like cruise flight. He said that this method leads to less of a pitching moment when trying to establish the glideslope.

I'll give it a shot, but I wonder if this technique is more suited to flying a jet rather than a 160hp piston.
Click to expand...
I doubt it. Flying an ILS is, at heart, a constant airspeed/constant rate descent.When you do it the way you described, setting power and pitching for 90 Kts, aren't you also targeting a 450 FPM descent rate as part of your ballpark*? He's just getting to the same place a slightly different way.

[*That's just a 3° glidepath at 90 KTS GS. At 120 KTS , it would be 600 FPM. I assume you learned that standard rule of thumb - GS X 5 or GS/2 and add a 0, GS meaning ground speed]
 
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When you fly an ILS with an autopilot the autopilot adjusts pitch to stay on the glide slope. The pilot adjusts the power to stay on airspeed. That is assuming you don't have autothrottles. That's probably why it's more natural for him to think of pitching for altitude and throttle for speed. Also, it's quicker to make corrections on the glideslope using pitch rather than power. But as many have said in this thread, it's all interconnected.
 
midlifeflyer said:
[*That's just a 3° glidepath at 90 KTS GS. At 120 KTS , it would be 600 FPM. I assume you learned that standard rule of thumb - GS X 5 or GS/2 and add a 0, GS meaning ground speed]
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Nope, I memorized common descent profiles based on airspeed for the aircraft I fly (either 90 or 120 kts) I like this tho.
 
Everskyward said:
When you fly an ILS with an autopilot the autopilot adjusts pitch to stay on the glide slope. The pilot adjusts the power to stay on airspeed. That is assuming you don't have autothrottles. That's probably why it's more natural for him to think of pitching for altitude and throttle for speed. Also, it's quicker to make corrections on the glideslope using pitch rather than power. But as many have said in this thread, it's all interconnected.
Click to expand...

Going along with the its all interconnected thing - if I am on my target airspeed and find I am low on the glideslope I will make a pitch adjustment and increase power at the same time. Pitch is an immediate correction and adding power maintains airspeed.

If you are not active with pitch and just make power adjustments, you will wallow around as the corrections are slow to take effect and there is usually some oscillation until the airplane will stabilize descent rate, airspeed and pitch on the new power setting.
 
labbadabba said:
Nope, I memorized common descent profiles based on airspeed for the aircraft I fly (either 90 or 120 kts) I like this tho.
Click to expand...
Then I think I see what he was getting at. No so much pitch/power vs power/pitch, but using a commonly taught mental calculation to anticipate the descent rate that will produce a 3° glidepath (which is what an ILS is). It gets you in the ballpark, just like your other configuration numbers do.

It also provides some valuable information about your groundspeed. If your IAS is 90 and a target 450 FPM is not keeping you on the glidepath, you know whether you have a tailwind or headwind and can better compensate with a power adjustment because you are anticipating what is needed rather than simply chasing the needle.

And if you have a GS readout (most of us do these days), it's even easier to get the proper descent rate to start with on a windy day using the quick calculation.
 
labbadabba said:
So, did my mock checkride with our chief pilot. He's a corporate pilot with 26,000 hours mostly turbine. He gave me a full endorsement so that was good but he did have some interesting pointers, one of which struck me as odd.

Typically to stabilize my decent, I set descent power, pitch for 90KIAS and adjust power based upon my VSI/Glideslope. This is the standard behind the power curve flying just like any VFR pilot would fly.

His suggestion for a 3-degree GS was to pitch for 450fpm on the VSI and set descent power for 90KGS. So in other words, pitch for altitude and power for speed like cruise flight. He said that this method leads to less of a pitching moment when trying to establish the glideslope.

I'll give it a shot, but I wonder if this technique is more suited to flying a jet rather than a 160hp piston.
Click to expand...
If you ever fly an airplane with a flight director, particularly a single-cue version, you "follow the bird" with pitch and control airspeed with power. This is not limited to jets.
 
aterpster said:
If you ever fly an airplane with a flight director, particularly a single-cue version, you "follow the bird" with pitch and control airspeed with power. This is not limited to jets.
Click to expand...

G1000s with the GFC700 autopilot do that. Those are the inputs to the autopilot, so, it's not surprising that they use pitch to control track.
 
Shocking how those flight directors and autopilots don't know that pitch controls airspeed and power controls altitude. One would almost be led to think the whole pitch/power debate is kind of silly. :D ;)
 
midlifeflyer said:
Shocking how those flight directors and autopilots don't know that pitch controls airspeed and power controls altitude. One would almost be led to think the whole pitch/power debate is kind of silly. :D ;)
Click to expand...
An old airline joke: An FAA inspector boards the jump seat during preflight. "Okay captain, what controls airspeed and what controls altitude?" The captain responds, "Power controls airspeed and elevator controls altitude." Fed, "You've got it backwards. Power controls alitude and elevator controls air speed." End of conversation. They start up, taxi out, and are eventually cleared into position to hold (line up and wait these days). The captain looks at the F/O and says, "Okay, when the tower clears us for takeoff I'll pump the yoke. When we get to 140 knots, then you apply takeoff power."
 
aterpster said:
An old airline joke: An FAA inspector boards the jump seat during preflight. "Okay captain, what controls airspeed and what controls altitude?" The captain responds, "Power controls airspeed and elevator controls altitude." Fed, "You've got it backwards. Power controls alitude and elevator controls air speed." End of conversation. They start up, taxi out, and are eventually cleared into position to hold (line up and wait these days). The captain looks at the F/O and says, "Okay, when the tower clears us for takeoff I'll pump the yoke. When we get to 140 knots, then you apply takeoff power."
Click to expand...
Yep. There's also a joke for those who insist on the reverse. I don't recall it exactly but it's probably something like, "Okay, when the tower clears us for takeoff, I'll pull back on the yoke. One we leave the ground add power. "
 
Okay, so I tried it last night. I pegged the VSI at 450fpm in descent and set power and trimmed for 90kts over the ground, all the while I cross-checked against the VSI. The Glide Slope was pinned right in the middle the whole time. The only time the needle moved is when I put in flaps and had to re-trim a bit.

In retrospect this makes a lot of sense. Following a glide slope is basically a constant rate descent, so it's only natural that the VSI would be the primary instrument in that case.
 
Yes, it works great unless there is a strong tailwind. Don't want the airspeed TOO slow.

For that case, you can use 120 knots GS and 600 FPM.

FYI, it's also a constant airspeed descent. Unless it's one of those really really long ILS's (KSNS ILS 31, for instance -- GS interception is at 5000, airport is at sea level).
 
MAKG1 said:
Yes, it works great unless there is a strong tailwind. Don't want the airspeed TOO slow.

For that case, you can use 120 knots and 600 FPM.
Click to expand...

Yeah, was considering that, flying with a tailwind changes things. I think if I can set 450 on the VSI and shoot for 90KIAS and adjust from there. Knowing that 60kts ground speed is 300 fpm and 120kts ground speed is 600fpm I should be able to adjust my decent on the VSI within that range pretty easily. I do like the idea of pegging my descent angle tho. The times that I've tried it have resulted in much more stable glide paths.
 
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