Instrument Training: Instrument Scan, Part 3

Proper instrument selection is your third priority

February's and April's "Instrument Training" discussed the first two steps of my four-step scan procedure. Step One emphasizes common sense and instrument flying's first priority -the undeniable principle of "attitude plus power equals performance." Step Two emphasizes proper thinking and the Inverted-V instrument scan. You scan the "trap door" and the "fine tuners" - the attitude indicator (AI), and the turn coordinator (TC) and vertical speed indicator (VSI). Remember, I use unique terms to help pilots identify and remember specific objectives. This month we'll discuss the remaining steps.

Step Three

You scan the primary instruments for specific numbers (quantitative information). A major error occurs if you make "the numbers" your primary scanning priority because aircraft control then requires too much attention, and your flight management functions - communication and navigation - receive too little attention. To avoid this problem and maintain the proper scan priorities, you must treat the primary instruments as the tertiary instruments, the third level of importance.

Pilots have three primary (tertiary) instruments for each flight maneuver - one for pitch, one for bank, and one for power. To identify which instruments they are, match the maneuver's numerical requirement for pitch, bank, and power to the instrument that provides that number. This task is easy to do. Study Figure 1 and the following examples.

For straight and level flight you need a specific altitude, heading, and power setting. Therefore, the altimeter is the primary pitch instrument, the heading indicator is the primary bank instrument, and the tachometer or manifold pressure (tach/MP) gauge is the primary power instrument. For level turns you need a specific altitude, turn rate, and power setting. The altimeter is primary for pitch, the TC is primary for bank, and the tach/MP gauge is primary for power.

For a straight climb you need a specific airspeed, heading, and power setting. The airspeed indicator is primary for pitch, the heading indicator is primary for bank, and the tach/MP gauge is primary for power. For a turning descent you need a specific airspeed, turn rate, and power setting. The airspeed indicator is primary for pitch, the TC is primary for bank, and the tach/MP is primary for power. Based on your visual flight training, the above relationships should make sense. While climbing or descending, you adjust pitch to maintain airspeed. While flying level, you adjust pitch to maintain altitude. Those relationships are correct for both visual and basic instrument flying because you have only one pitch requirement, and therefore, you need only one primary pitch instrument.

Advanced instrument flying introduces new tasks. You must maintain two pitch requirements simultaneously - airspeed and altitude, or airspeed and vertical speed (ILS approach). Four of Figure 1's maneuvers have asterisks to indicate that airspeed is the primary power instrument, not the tach/MP gauge. Two of the three primary instruments for these maneuvers are pitch instruments. The airspeed indicator can be a pitch or a power instrument. When airspeed is your only pitch requirement, the airspeed indicator is your primary pitch instrument. When airspeed and altitude or airspeed and vertical speed are your two pitch requirements, the airspeed indicator becomes your primary power instrument and the altimeter or the VSI is your primary pitch instrument.

No pitch and power arguments, please. I know the theory, I've heard all the arguments, and I agree. That stuff is correct. But, in the real world, you must deal with the effects of wind and turbulence. I'm explaining what works best when you fly an airplane in weather, not what supports classroom or flight simulator theory.

Figure 2 depicts instrument categories based on pitch, bank, or power. The airspeed indicator has two roles, as does the AI - indicating pitch and bank. The AI becomes a primary bank instrument only when you need a specific bank angle for a maneuver such as a steep turn, a measurement made by the pointer and indices at the top of the instrument.

In Step Two (April 1998 "Instrument Training") you music-scanned the Inverted-V, and you do the same with the primary instruments in Step Three, but the musical count increases by one number because you add one additional instrument. Figure 3 depicts your eye movement when you scan the primary instruments for a level turn at a specific airspeed. Look at the AI every time you say "and." Every time you say a number (one, two, or three), look at one of the three primary instruments. Here is the musical beat - "and one, and two, and three; and one, and two, and three..." To establish the proper timing, repeat this sequence out loud and slowly.

When the tach/MP gauge is the primary power instrument, it requires little attention because you will have set power during Step One. Consequently, you scan only three instruments in most cases - the AI and the primary pitch and bank instruments.

Step Four

In Step Four you scan all the flight instruments for deviations and fine-trim the airplane for hands-off flight. It can take 15 seconds to reach Step Four because you need up to five seconds each for the first three steps. When you reach the last step, your scan pattern changes from the music scan to a circular scan (Figure 4). Your eyes will welcome the change because the circular scan is less fatiguing.

You will not always reach Step Four. If you have to make frequent attitude or power changes (because of turbulence, instrument approaches, and coordination maneuvers) you'll return frequently to Step One during or after Step Two or Step Three. Whenever you redirect the aircraft - attitude or power change - you must return to Step One.

A mental concern might interrupt your scan pattern occasionally, and your eyes will move immediately to the instrument that caught your attention. You should restart the circular scan from that point, but your instincts may tell you to restart at the AI.

Proper cockpit management is what happens when you perform other cockpit tasks - frequency changes, navigation computations, chart reference or organization, checklists, and systems monitoring - during Step Four rather than Steps One, Two, or Three.

If you look at the AI before leaving the flight instruments and then cross-check the AI - and only the AI - while you perform that task, your success is guaranteed. If you look at any other instrument you're wasting time because the other flight instruments will mind their manners if you maintain the desired attitude. When you finish, return to the AI and review Steps Two and Three to validate the AI and check for trend of movement and primary instrument deviations.

Four-Step Summary

1. Scan the attitude indicator and the tachometer or manifold pressure gauge while you establish the desired attitude and power setting. Rough-trim the elevator if you need to and proceed to Step Two.
2. Music scan the Inverted-V in order to validate the AI and check the TC and VSI trends of movement. If you can't validate the AI, figure out which instrument or system is at fault by using the triangle of knowledge. If your trend of movement is incorrect, return to Step One and restart the scan procedure. If your validation and trend are correct, proceed to Step Three.
3. Music scan the primary instruments. If "the numbers" are incorrect, return to Step One and restart the scan procedure. If "the numbers" are correct, proceed to Step Four.
4. Circular scan the flight instruments, and fine-trim the airplane for hands-off flight. If something distracts you from your scan, always check the trap door (AI) before leaving, while gone, and upon returning to the flight instrument group.

Practice my four-step scan procedure until it becomes habitual. You cannot manage an instrument flight properly if the flight instruments demand your constant attention. As you gain experience, your eyes won't move that much, and you'll look at the six flight instruments as a group and let your brain execute the four steps I've discussed. Instrument flying becomes a cinch because you now have lots of time for flight management and you'll never be victimized by an instrument or system failure.

Editor's Note: More detailed information on the Four-Step Scan and instrument training in general is available in the author's Instrument Pilot Flight Training Manual, published by Skyroamers Publications (800/406-5780 or www.skyroamers.com).