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Primary+Supporting vs. Control+Performance for BAI

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Instrument Rating

I don't think I fully understand how the primary+supporting instrument method works for BAI. Is there a simple way to understand and use the primary+supporting method? What are the advantages and disadvantages of each method, and which do you prefer to use or teach to your students? As a student, I feel it's easier to understand and to actually use the control+performance method in the air.

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2 Answers

  1. Best Answer


    Mark Kolber on Nov 11, 2014

    actually use the control+performance method in the air.

    Control/Performance and Primary/Supporting used to be one of “those” arguments. I think the mistake often made is to think that they are scan techniques. The “mistake” is enhanced by the fact that C/P is closer to the scans usually used. But they are not scan techniques. They are methodologies for understanding and interpreting the instruments. Neither is inherently “better” than the other.

    The following is a copy/paste of a post I did years ago. My thoughts only, not gospel:

    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 selcting 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

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  2. Drew on Nov 13, 2014

    Thanks, Mark. This was helpful.

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