primary inst while on Glide slope?

[Lead Sled]

not be be a wise-a$$, but my primary instrument on the ILS IS the localizor and GS needles

follow those and everything else works out, hell you even are at VREF at 50 feet and land at the 1000 foot markings

can't ask for much more than that

(above is based on airplane being properyly configured per POH/etc during approach)

I was going to say that the primary instrument on the ILS is the flight director.

'Sled

 

[Tinstaafl]

It's a form of linked chain concept.

If you, say, pitch the a/c to correct a GS error using the GS to tell you when to stop pitching then you'll overcorrect, resulting in flying through the GS and a mirror image of the problem. This yo-yo-ing results in the GS being seen -momentarilly - as the a/c passes from one side to another. As a/c speeds, mass & inertia increase, and proximity to the transmitter decreases then the pilot responses will not be adequate to constrain the flight path within the required tolerances.

So, the next step back from the direct reading instrument (the GS display), is to establish a nominal rate of descent for the rate of closure that will match the GS angle. At best the a/c will exactly parallel the GS (if the descent started whilst on the GS), at worst the descent will diverge at a rate inversely proportional to the distance from the transmitter. Of course this assumes the ROD is exactly correct. If the descent rate is incorrect then it will result in either closing with the GS (yay!) or diverging from it (boo, hiss).

Trouble is that pitching to establish a descent rate by reference to a normal VSI results in a similar GS display ie yo-yo-ing.

What next? Use the AI/AH to set a constant pitch angle. If power is unchanged then ROD is roughly linearly proportional to pitch attitude, at least close enough over small changes to be useful. Now the key becomes 'check the GP to determine location WRT to the GS, check VSI to determine ROD WRT a previously calculated approx. 'ideal' ROD --> adjust pitch attitude by a small amount WRT to the AI/AH & wait for a stabilised (or nearly stabilised) new ROD in the appropriate sense --> wait for change of position WRT to the GS to be indicated on the GS display. If the rate of change is insufficient then reiterate.

NB: At some point in this process will be found a pitch attitude that very nearly 'freezes' the GS needle. Remember that attitude for when the GS is eventually regained then use it as the subsequent baseline reference point.

This results in a far more stable & controlled GS than the other scenarios I mentioned.

The principle in the above GS example is no different to establishing a CDI intercept. I don't think anyone would advocate rolling the a/c until they saw the CDI move? Or, one step back from that, roll the a/c until they saw the HDG reach the desired point? Try that a 180deg required HDG change... . Instead we all roll the a/c by referencing the AoB on the AI/AH, holding the desired AoB while the a/c turns, then holding the new heading while waiting for the CDI to move etc.

So... in my view the AI/AH is the primary instrument(s) along with power & the ball.
Sorry if this gets a bit basic, but I found it difficult to explain my point without resorting to first principles.

 

[100LL... Again!]

The LOC and GS capture lights on autopilot panel

 

[nosehair]

If you're looking to maintain the centerline of the LOC and GS, wouldn't your primary instrument be the HSI or VOR/LOC/GS?

Using your nav instruments keeps your needles centered...everything else is supporting?

IE.
LOC/GS = Primary for Bank and Pitch
ASI = Primary for Power

DG/AI = Supporting for Bank
ALT/VSI/AI = Supporting for Pitch
Tach/MAP Gage = Supporting for Power

Perhaps I'm making this too simple...to me what makes sense is on an ILS you maintain the GS and LOC in the center. To do that, you "fly the needles" all the way to DH.



-mini

mini has it!
When this is practiced, the initial overcontrolling will eventually stop. You will learn to percieve the slightest movement of the needles and make an ever-so-slight control input to correct so that the needles don't get even a dot away.
The trouble with setting an attitude and power setting and don't chase the needles is, that it works fine with little or no wind or turbulance. But with strong crosswinds or large vertical movements, as in thunderstorms, the "primary instrument" technique will always work. Setting an attitude won't.

 

[Vandal]

ADI, crosscheck VSI and airspeed.

 

[KeroseneSnorter]

It's a form of linked chain concept.

If you, say, pitch the a/c to correct a GS error using the GS to tell you when to stop pitching then you'll overcorrect, resulting in flying through the GS and a mirror image of the problem. This yo-yo-ing results in the GS being seen -momentarilly - as the a/c passes from one side to another. As a/c speeds, mass & inertia increase, and proximity to the transmitter decreases then the pilot responses will not be adequate to constrain the flight path within the required tolerances.

So, the next step back from the direct reading instrument (the GS display), is to establish a nominal rate of descent for the rate of closure that will match the GS angle. At best the a/c will exactly parallel the GS (if the descent started whilst on the GS), at worst the descent will diverge at a rate inversely proportional to the distance from the transmitter. Of course this assumes the ROD is exactly correct. If the descent rate is incorrect then it will result in either closing with the GS (yay!) or diverging from it (boo, hiss).

Trouble is that pitching to establish a descent rate by reference to a normal VSI results in a similar GS display ie yo-yo-ing.

What next? Use the AI/AH to set a constant pitch angle. If power is unchanged then ROD is roughly linearly proportional to pitch attitude, at least close enough over small changes to be useful. Now the key becomes 'check the GP to determine location WRT to the GS, check VSI to determine ROD WRT a previously calculated approx. 'ideal' ROD --> adjust pitch attitude by a small amount WRT to the AI/AH & wait for a stabilised (or nearly stabilised) new ROD in the appropriate sense --> wait for change of position WRT to the GS to be indicated on the GS display. If the rate of change is insufficient then reiterate.

NB: At some point in this process will be found a pitch attitude that very nearly 'freezes' the GS needle. Remember that attitude for when the GS is eventually regained then use it as the subsequent baseline reference point.

This results in a far more stable & controlled GS than the other scenarios I mentioned.

The principle in the above GS example is no different to establishing a CDI intercept. I don't think anyone would advocate rolling the a/c until they saw the CDI move? Or, one step back from that, roll the a/c until they saw the HDG reach the desired point? Try that a 180deg required HDG change... . Instead we all roll the a/c by referencing the AoB on the AI/AH, holding the desired AoB while the a/c turns, then holding the new heading while waiting for the CDI to move etc.

So... in my view the AI/AH is the primary instrument(s) along with power & the ball.
Sorry if this gets a bit basic, but I found it difficult to explain my point without resorting to first principles.

Holy Crap, Tin!

Loc, G/S, Hdg, Alt, A/S, Repeat until minimums.......small corrections as necessary.

Just fly the freakin thing!!! Works in a 140 as well as a 757!

It ain't rocket science, each student needs to find what works for him/her.

I had a kid one time that got some screwy formula from a retired Air Force Col. that was teaching ground school, He was doing great until he decided to try to use that formula for decent FPM , intercept angle, yadda, yadda, yadda, Once I got him to forget all that crap and just fly the airplane he could nail an ILS no problem!

 

[midlifeflyer]

2¢:

If the question is asking "According to official FAA doctrine, under the 'primary/supporting' method of flight instrument interpretation..." the answer is the VSI. Flying the glideslope is treated as a constant rate descent.

If we're talking about the in-flight techniques that put that theory into practice, I'll leave the argument about the "one true way" to the same people who argue about pitch and power.

 

[nosehair]

"According to official FAA doctrine, under the 'primary/supporting' method of flight instrument interpretation..." the answer is the VSI. Flying the glideslope is treated as a constant rate descent.

mmm...Midlife, do you read that anywhere specific in the FAA-H-8083 Instrument Flying Handbook?, or any other FAA publication?; that flying the glideslope is treated as a constant rate descent??

Trouble is, the FAA Handbook talks about the primary/supporting method in the context of basic flight instrument scan. I can't see where they flow that scan into the nav instruments, which essentially become primary when you consider the basic statement in the bottom right corner of page 4-3: "The instruments that provide the most pertinent and essential information will be refered to as primary instruments."

Flying the glideslope as if it were a constant rate descent won't work - because it's not. Oh, you might have a day or two once or twice a year when there's a dead calm and you can "set it and forget it" on the glideslope. If it wern't for wind and slight turbulance, these things would be as easy to fly as drivin' a car.

But wind, my friend, is the great equalizer.

The glidesope needle tells you what to do with the VSI.

When you are trying to hold a constant altitude, the Altimeter tells you what to do with the VSI, therefore, the Altimeter is the Primary instrument for pitch in level flight, because the altimeter tells you what to do with pitch. My "technique" of controlling that pitch is with the VSI, but that is my "technique". Others use the attitude indicator, that is thier "technique", but we all are using the Altimeter to tell us what to do with the pitch.

When on the glideslope, we are using the glideslope needle to tell us what to do with pitch, then using the VSI to control that pitch, or, depending on personal "technique", using the needle itself to gage pitch input.

I know you know all this, but my original question is, have you found any FAA pub that even talks about the "techniques" of localizer or glideslope capture and/or navigation?

 

[Pull & Rotate]

Primary instrument while on the ILS? Thats an easy one. GPWS.

 

[midlifeflyer]

mmm...Midlife, do you read that anywhere specific in the FAA-H-8083 Instrument Flying Handbook?, or any other FAA publication?; that flying the glideslope is treated as a constant rate descent??

Trouble is, the FAA Handbook talks about the primary/supporting method in the context of basic flight instrument scan. I can't see where they flow that scan into the nav instruments,

No, I haven't seen anything official.

But what you say is exactly the point. The "primary supporting" theory of instrument interpretation is a =flight= instrument methodology for aircraft control - how do we verify that the airplane is doing what it's supposed to do - in this case descend at both a desired airspeed and at a desired (although changeable) decent rate. It deals exclusively with airspeed control, not navigation.

In the glide slope context, yes, we're following the needle. But we also know that following needles leads to overcorrection. If we need to correct for lateral drift, we turn a specific number of degrees. Similarly, if the glide slope needle is low, we don't just pull power to idle (well, some of us probably do ) we make a power and pitch change that adjusts our descent rate to something specific. That's rate descent control (or at least one of the reasons we focus on rate control in early attitude instrument training) . It's sort of a traditional separation of aviate and navigate.