Are you one of those pilots who think the engine primer is one of the primary instruments? Nahhh, no one would mix those two things up, right? A few pilots might, however, confuse the definition of primary instruments. In fact, they do. I see it happen frequently during instrument proficiency flights.
There are three primary instruments for any given flight condition: one for pitch, one for bank, one for power. For instance, during instrument flight, all initial attitude changes are made on the attitude indicator. You simply look at the attitude indicator and place the airplane in the attitude desired. But the attitude indicator is only a "ball park" instrument. It doesn't give you the finely detailed information necessary to maintain a specific pitch or bank condition. That's the job of the primary instruments.
Of course, all this is a bit complicated because the primary instruments change based on the flight attitude chosen. The primary pitch and bank instruments for straight-and-level flight are different from those of a climbing turn.
Here is one of the easiest methods I've found for identifying which instruments are primary for any given flight condition. Slice off the top quarter inch (the sticky side) from six Post It Notes. Label and place them under the six instruments as shown in Figure 1. I recommend Post Its instead of stronger forms of adhesive materials. Attempting to remove industrial tape from the panel might result in pulling off enormous slabs of plastic, as well as popping a few instruments out of their sockets.
Now you have an easy means of identifying which instruments are primary for any given condition of flight. Let's examine what those words mean. The word START, located under the attitude indicator, signifies that all major attitude changes commence here. Simply select the new attitude desired on this instrument.
Let's assume you want to transition from a climb to straight-and-level flight. Start at the attitude indicator and put the airplane in an approximately straight-and-level flight condition. Then look at the instruments having the words STRAIGHT and LEVEL underneath them. These will be the primary bank and pitch instruments for that given flight condition.
The heading indicator and the altimeter are the primary instruments for bank and pitch. In other words, they are the most useful ones to look at to accomplish straight-and-level flight. From the attitude indicator, go to the word STRAIGHT, and look at that instrument (the heading indicator). See if it's doing what you want it to do, then immediately return to the attitude indicator, making any necessary changes in bank to keep the airplane going straight.Next, leave the attitude indicator and go to the word LEVEL, and look at that instrument (the altimeter). See if it's doing what you want it to do, then immediately return to the attitude indicator, making any changes in pitch to keep the airplane level. Repeat this process between the primary instruments as many times as is necessary to put the airplane in the precise straight-and-level flight condition desired.
Suppose you were in straight-and-level flight and wanted to enter a climbing turn. You start the attitude change with the attitude indicator, then move to the instrument with the word CLIMB under it. The airspeed indicator is now your primary pitch instrument for a climb (or descent). You then return to the attitude indicator, making any adjustments in pitch necessary to give you the desired airspeed.
Next you move to the instrument with the word TURN underneath it. The turn coordinator becomes your primary bank instrument while in a turn. Observe its reading and return to the attitude indicator, making whatever bank adjustments are necessary to give you a standard rate turn. In all the above-mentioned flight conditions, the tachometer is the primary power instrument. For the most part, you don't need to look at the tachometer when entering a climb or descent in most small airplanes with fixed-pitch propellers. Simply apply full power or sufficiently retard the power and select the appropriate attitude.
While leveling off from a climb or descent to straight-and-level flight, initially place the throttle (by feel only) in the approximate cruise power position when the desired airspeed is reached. Then leave the attitude indicator, glance at the tachometer, adjust power if necessary and return to the attitude indicator.
There is one condition, however, where the tachometer is not a primary power instrument. Suppose you wanted to make a constant rate descent at 500 feet per minute. This is typically done on an ILS approach where a given descent rate for a given groundspeedproduces a path parallel with the glide slope. Essentially, you're making a straight descent at a constant rate while keeping the airspeed constant.
When you maintain a specific descent rate, the VSI becomes primary for pitch (RATE), the heading indicator is primary for bank (STRAIGHT) and the airspeed becomes primary for power (POWER). Simply look at each instrument, interpret its movement or position then return to the attitude indicator to make any necessary adjustments.
A few years ago I experimented with 10 instrument students using this primary instrument identification procedure. After approximately 10 hours of basic instrument training (in an airplane or simulator or both), I removed the Post Its from underneath each instrument. As I expected, these students acquired the habit of knowing which instrument were primary for any given flight condition without dependency on the Post It prompts.
The intent here is not to teach instrument scan. This is a slightly more complex subject. Rather, my intent is to teach an easy way to recognize the primary instruments for any given flight attitude in hopes of improving your scan efficiency.
Excerpted and modified from Rod Machado's Instrument Pilot's Survival Manual.
For more information on this subject, see "Instrument Training: Instrument Scan, Part 3," "Instrument Training: Instrument Scan, Part 1," "Instrument Training: Instrument Scan, Part 2," and "Instrument Training: Instrument Interpretation."
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