Difference? - Control/Performance vs. Primary/Supporting

[eetrojan]

I've been reading numerous sources, but am still struggling to find a definitive difference between the "control & performance" and "primary & supporting" concepts.

Here's my potentially incorrect attempt to describe the process of using both methods for maintaining straight & level flight, and it sounds like they're just different ways of saying exactly the same thing.

Under control/performance, I start with the AI and use just it to select/maintain an attitude (pitch and bank) that in combination with my power setting I correlate with constant-altitude, wings-level flight, and then I cross-check the performance instruments to make sure I’m getting the desired performance, maintaining present control forces if all is good, or making smooth adjustments if required. Presumably, this cross-check would involve my checking the ALT, HI, and ASI gauges.

Under primary/supporting, I start by mentally dividing my current task at hand into pitch, bank, and power, and starting with my AI at the heart of the scan, radially cross-check my “primary” pitch instrument (ALT), bank instrument (HI), and power instrument (ASI), maintaining present control forces if all is good, or making smooth adjustments if required.

Color me confused... Using the AI and then checking the "performance" instruments (ALT, HI, and ASI), seems pretty darn close to using a succession of "primary" instruments (ALT, HI, and ASI) with the AI at the "heart" of the scan/cross-check. The "heart" of the scan language comes from Machado's books, and my own school's syllabus.

Am I missing something? Any help?

Maybe a difference would be more apparent in a more transitional phase of flight?

It seems like it may be subtle matter of philosophy? One is more holistic and the other more granular?

 

[bobmrg]

That "distinction" is for knowledge exams. In the real world, you will develop your own scan...which will be a combination of both. I favor the "selected radial" scan, in which your eyes return to the attitude indicator after a glance at the altimeter, the heading indicator, the nav display, the turn coordinator, etc. Using that scan, your eyes never go directly from one instrument to another except by way of the AI. This is based on a six-pack, of course; glass offers other methods. There are a bunch of suggested scans...no one is best.

Bob Gardner

 

[poadeleted20]

It seems like it may be subtle matter of philosophy? One is more holistic and the other more granular?

To me, it's more an issue of terminology. With p/s, each instrument may be either primary or supporting at any given time depending on exactly what you're doing, and, for example, which is which changes four times when making a turn -- rolling in from level flight, maintaining the turn, rolling out of the turn, and then again maintaining level flight. OTOH, with C&P, it's pretty simple -- you have one attitude control instrument which is always your attitude control instrument, one power instrument which is always your power instrument, and everything else is always a performance instrument. So which one do you think is easier for the instructor to teach and the trainee to learn?

 

[James331]

That "distinction" is for knowledge exams. In the real world, you will develop your own scan...which will be a combination of both. I favor the "selected radial" scan, in which your eyes return to the attitude indicator after a glance at the altimeter, the heading indicator, the nav display, the turn coordinator, etc. Using that scan, your eyes never go directly from one instrument to another except by way of the AI. This is based on a six-pack, of course; glass offers other methods. There are a bunch of suggested scans...no one is best.

Bob Gardner

That.

There is a reason we have backup AIs.

 

[jordane93]

That "distinction" is for knowledge exams. In the real world, you will develop your own scan...which will be a combination of both. I favor the "selected radial" scan, in which your eyes return to the attitude indicator after a glance at the altimeter, the heading indicator, the nav display, the turn coordinator, etc. Using that scan, your eyes never go directly from one instrument to another except by way of the AI. This is based on a six-pack, of course; glass offers other methods. There are a bunch of suggested scans...no one is best.

Bob Gardner

This.

 

[kgruber]

That "distinction" is for knowledge exams. In the real world, you will develop your own scan...which will be a combination of both. I favor the "selected radial" scan, in which your eyes return to the attitude indicator after a glance at the altimeter, the heading indicator, the nav display, the turn coordinator, etc. Using that scan, your eyes never go directly from one instrument to another except by way of the AI. This is based on a six-pack, of course; glass offers other methods. There are a bunch of suggested scans...no one is best.

Bob Gardner

Cut this post and frame it.

 

[eetrojan]

Thanks all. Particularly to Bob for his "frameable" post!

 

[denverpilot]

That "distinction" is for knowledge exams. In the real world, you will develop your own scan...which will be a combination of both. I favor the "selected radial" scan, in which your eyes return to the attitude indicator after a glance at the altimeter, the heading indicator, the nav display, the turn coordinator, etc. Using that scan, your eyes never go directly from one instrument to another except by way of the AI. This is based on a six-pack, of course; glass offers other methods. There are a bunch of suggested scans...no one is best.

It's really difficult to add to this. I found after I had to "just do it" that I also flew better with the radial method. If I started leaving the AI out of the scan things got squirrelly much faster.

 

[MarkZ]

During IMC flying, I use the star method. Centered on artificial horizon, correlate with turn coordinator and VSI. Using airspeed, altimeter, and heading to gauge performance. Check OBS for result.

During VMC flying, head out window instead of artificial horizon, same scan otherwise.

YMMV

 

[poadeleted20]

Bob's post is great practical advice, but regrettably won't help you on the instrument written test, where primary/supporting and only primary/supporting is tested.

 

[eetrojan]

Bob's post is great practical advice, but regrettably won't help you on the instrument written test, where primary/supporting and only primary/supporting is tested.

Thanks Ron. I have that down fine for the written. I was really trying to think about the differences (or lack thereof) for some future flying...

 

[poadeleted20]

Thanks Ron. I have that down fine for the written. I was really trying to think about the differences (or lack thereof) for some future flying...

I'd suggest dumping p/s from your head as soon as you get the passing written score report. Try to apply p/s in the plane and you end up spending too much time and brain power trying to remember which instrument is which in any given situation. C&P doesn't require thinking, just memorizing the baseline attitude/power settings for each phase of flight (or writing them on a card you stick where you can see it) and then adjusting them as needed to get the desired performance. Go find a copy of Peter Dogan's "Instrument Flight Training Manual" for practical instrument flying recommendations.

 

[midlifeflyer]

Although, like pitch vs power, crab & kick vs slip, etc, each method tends to have its own adherents, in some cases religious zealots. But they're really just two approaches to teaching instrument interpretation. I think the biggest mistake is in thinking that either is a scan technique.

Primary/Secondary, which was the only approved FAA method for years, focuses on which instrument provides the most pertinent information for a given flight condition. So, for example, in straight and level flight

⦁ the DG is primary for bank because if the DG isn't moving, you aren't turning
⦁ the altimeter is primary for pitch because if the AI isn't changing, you are level
⦁ the AI isn't primary for, say, pitch because, while it may be a direct indication of attitude, level on the AI doesn't necessarily mean level in reality (low power and level AI usually means a descent)
⦁ the other instruments that indicate bank (AI, TC) and pitch (AI, VSI, ASI) are secondary - they back up the primary instruments.

Control/Performance, which has been used just about forever in military flight training, focuses on how we actually control the airplane (both VFR and IFR) - by slecting an attitude (control) and then confirming that the airplane is behaving as we expect it to (performance). So, in almost all flight conditions, the AI is the control instrument for our position (level, climb, descent, turn....). The other instruments tell us if what we're reading on the AI is correct.

IMO, P/S's strength is an understanding of how the each instrument works and how they work together. P/S's primary weakness (in addition to being harder for most to understand) is that is's a bit more theoretical and doesn't really reflect how we actually fly the airplane. C/P's strength is that it reflects how we actually fly the airplane. It molds theory to fit practice rather than the other way around. It's primary weakness is that it's not very specific about how to control the airplane when the control instrument is gone (partial panel).

Interesting: notice how the weakness of one is compensated for by the strength of the other

 

[flyingron]

C'Ron obviously has it nailed. Much like many other things (like the inane definition of controlled flight and the bogus educational theory on the FOI...which they fortunately exempt real teachers from having to study as it causes their heads to explode), this is just one of the pieces of FAA nonsense you learn for the written and forget.

Dogan (and hence the PIC course) teaching of scan and Command-Performance aspects of instrument aircraft control are much more grounded in reality.

 

[dtuuri]

Color me confused... Using the AI and then checking the "performance" instruments (ALT, HI, and ASI), seems pretty darn close to using a succession of "primary" instruments (ALT, HI, and ASI) with the AI at the "heart" of the scan/cross-check. Am I missing something? Any help?

I think you're confusing the instrument scan with instrument interpretation. Also, for simple straight and level flight under your scenario, airspeed is not a primary power instrument. When you ask yourself if you need to change your power setting, do you look at your ASI? No.

Here's my treatise on attitude instrument flying: http://www.avclicks.com/Flash2/Its_Not_Your_Flying/index.html .

The first 19 slides reclaim the essential instrument flying fact from Howard Starks' method, "Don't tip the plane too much!" It's as fundamental today, in both modern systems, as ever.

dtuuri

 

[Bill Watson]

OT: Once you have it all set up in a nice smooth layer of IMC, and you want to smoothly hand fly the plane with minimum effort, use the turn coordinator to keep the wings level. As long as the engine noise stays the same, all good.

I wish I still had one of those.

 

[eetrojan]

I think you're confusing the instrument scan with instrument interpretation. Also, for simple straight and level flight under your scenario, airspeed is not a primary power instrument. When you ask yourself if you need to change your power setting, do you look at your ASI? No.

I might be confused, but in case it helps, I was trying to say that I would use a radial cross-check regardless of whether I was using c/p or p/s. Does that seem wrong for some reason?

On the ASI being primary for straight and level flight, the books I’m reading say that’s the case. I’m not talking about the phase of flight that involves changing power, but rather the phase of flight where I’m maintaining power. Maybe I needed to indicate that it was straight & level flight at “constant airspeed.”?

To help further explain my potentially incorrect understanding, Machado says that in straight & level flight, “the airspeed indicator is primary for power when we want to maintain a constant airspeed.” Also, here’s an excerpt of his primary/supporting table for different scenarios:

Here's my treatise on attitude instrument flying: http://www.avclicks.com/Flash2/Its_Not_Your_Flying/index.html.

The first 19 slides reclaim the essential instrument flying fact from Howard Starks' method, "Don't tip the plane too much!" It's as fundamental today, in both modern systems, as ever.

dtuuri

I watched that deck before (and really love your materials by the way). However, I’m still left with the impression that the difference between c/p and p/s is more semantic than real.

My question about finding a real difference between c/p and s/p stems from my observation that c/p sort of involves s/p in that scanning the “performance” instruments inherently implicate the s/p principals when it comes to which instruments should be prioritized or ignored during the scan. And, conversely, s/p is kind of like c/p in that it inherently involves the AI if you use the radial-scanning technique.

Probably over-thinking it, but there it is.

 

[dtuuri]

I might be confused, but in case it helps, I was trying to say that I would use a radial cross-check regardless of whether I was using c/p or p/s. Does that seem wrong for some reason?

The scan is one thing, interpreting what you scanned is another. The "primary" instrument is the one that answers the question(s), "Do I need to change my (pick one) pitch, bank or power?" It seemed to me you were equating the primary instruments to a type of scan pattern rather than to part of the interpreting process which is the other fundamental skill in the FAA's view.

Maybe I needed to indicate that it was straight & level flight at “constant airspeed.”?

Yes, that's a game changer. In normal cruise you'll set power and refer to power instruments to keep it, airspeed is what it is.

I watched that deck before (and really love your materials by the way). However, I’m still left with the impression that the difference between c/p and p/s is more semantic than real.

I think it's important to keep perspective on the actual amount of time that's needed in teaching attitude instrument flying no matter the method--it's very short. A case could be made that you should already know enough about it after you passed the private license task that requires a demonstration of basic instrument skills. It's easy to succumb to paralysis of analysis with this stuff. In the very beginning, say the first couple of hours, it helps get the student on the right track by asking which instrument tells them they need to make a change in pitch, bank and power during various maneuvers. Once they get the hang of it, it's time to move on. Bottom line? It doesn't matter a lot which system is better, since it doesn't take that much time to acquire basic instrument skills anyway. Of course, there are exceptions, not everybody seems to be able to 'get it'. The difficulty is in learning to apply those skills in the IFR system.

My question about finding a real difference between c/p and s/p stems from my observation that c/p sort of involves s/p in that scanning the “performance” instruments inherently implicate the s/p principals when it comes to which instruments should be prioritized or ignored during the scan. And, conversely, s/p is kind of like c/p in that it inherently involves the AI if you use the radial-scanning technique.

Probably over-thinking it, but there it is.

If the scan you use is the same for either system (it is) then the difference lies in how you interpret what you scanned. The p/s system lets you rely on your intuition, in my view, and move on to the more interesting things a bit sooner.

dtuuri

 

[MauleSkinner]

C'Ron obviously has it nailed. Much like many other things (like the inane definition of controlled flight and the bogus educational theory on the FOI...which they fortunately exempt real teachers from having to study as it causes their heads to explode), this is just one of the pieces of FAA nonsense you learn for the written and forget.

Dogan (and hence the PIC course) teaching of scan and Command-Performance aspects of instrument aircraft control are much more grounded in reality.

Note that Control/Performance has made its way into the Instrument Flying Handbook.

 

[petrolero]

Color me confused... Using the AI and then checking the "performance" instruments (ALT, HI, and ASI), seems pretty darn close to using a succession of "primary" instruments (ALT, HI, and ASI) with the AI at the "heart" of the scan/cross-check. The "heart" of the scan language comes from Machado's books, and my own school's syllabus.

Color me confused also. And I agree this is a book answer for book answer's sake.

I never could understand the difference between these two ideas. It's the same thing stated two ways as if there is a difference. But if it can be argued you better believe there are pilots out there who will pound fist on table about it.

You use one instrument to establish the maneuver and others to see how it's going and make fine adjustments. Simple. I never understood why they made such a BFD out of this.

And scan patterns... "Yes I use the Inverted B scan"... WTF? I dare say no one really flies that way.

 

[denverpilot]

Note that Control/Performance has made its way into the Instrument Flying Handbook.

Stupid spreads. Natural law. LOL

 

[MauleSkinner]

... And scan patterns... "Yes I use the Inverted B scan"... WTF? I dare say no one really flies that way.

Scan patterns are primarily there to give people a way to avoid fixation as they learn to fly instruments.

Whether "no one" really flies that way, I can't say, but with the exception of the Dutchess that I did my multi engine rating in, I've never flown a multi-engine airplane with a "standard" panel, so none of the scan patterns could be used.

 

[petrolero]

Scan patterns are primarily there to give people a way to avoid fixation as they learn to fly instruments.

Whether "no one" really flies that way, I can't say, but with the exception of the Dutchess that I did my multi engine rating in, I've never flown a multi-engine airplane with a "standard" panel, so none of the scan patterns could be used.

I use a cantilevered radial split-S scan myself.

 

[MauleSkinner]

I use a cantilevered radial split-S scan myself.

"Use your Radial-G!"
--Skipper

 

[eetrojan]

So, "scans" are really just the visual equivalent of "happy feet" on the rudder pedals?

 

[MauleSkinner]

So, "scans" are really just the visual equivalent of "happy feet" on the rudder pedals?

I'd say "standard" scan patterns probably relate pretty closely to that.

 

[midlifeflyer]

So, "scans" are really just the visual equivalent of "happy feet" on the rudder pedals?

Kinda.

Scan is how you choose to move from instrument to instrument to acquire information to confirm what you think the airplane is doing and check for discrepancies between instruments providing similar information ("cross-check"). Some standard types but can be very individualistic. Many use one (or more) scan for maneuvering and another for long term straight and level.

P/S and C/P are methodologies of how to process that information, understand when information two or more instruments are giving you conflict, and guidance on how to resolve the discrepancy (AI showing a bank but DG not moving, TC level and compass not really changing although it's bouncing around)