Beyond the basics

If an instrument rating is not at the top of your to-do list as a new pilot, you should at least consider expanding your knowledge of instrument-flying technique through some extra time under the hood-or your view-limiting device of choice-with an instructor. The instrument training you received as a student pilot, while important, was rudimentary by comparison to a comprehensive instrument flight rules (IFR) curriculum.

The first stage of instrument training is excellent insurance for both night flying and inadvertent flight into reduced visibility conditions. It should teach you how to properly scan the instruments, interpret what they are telling you, and control the aircraft by referring to the instruments.

Most instrument flying manuals thoroughly cover instrument scan and aircraft control, but the subject of instrument interpretation is often slighted. One would assume that interpretation requires you to look at an instrument, determine what it is indicating, and evaluate how that will affect you. That simplistic, basic understanding is true, but in reality, instrument interpretation is far more involved. When it is properly taught, instrument flying becomes much easier.

Private pilots normally have only one pitch requirement-airspeed or altitude. If climbing or descending at a constant power setting, they control airspeed with pitch; if maintaining altitude with a constant power setting such as cruise power, they control altitude with pitch.

Private pilots and instrument pilots have only one bank requirement-a standard rate turn using the turn coordinator, a constant heading using the heading indicator, or a constant bank angle using the attitude indicator or the Earth's horizon during visual flight.

Here's the catch. Instrument pilots flying under IFR frequently have two pitch requirements-airspeed and altitude during level flight, or airspeed and vertical speed during constant-airspeed, constant-vertical-speed climbs or descents. Now, the question becomes airspeed control and altitude control. How do you do it? The ensuing debate has caused many heated arguments. Here are two typical answers.

"I can do everything with just power providing the elevator is properly trimmed." That is certainly true in smooth air or in a ground training device that has the aerodynamic responses of an airplane, but it is worthless in turbulence-a frequent occurrence during instrument flight.

"I always control airspeed with pitch and altitude or vertical speed with power." That, too, works, but it compromises the precision that instrument flight requires because power responses are slower than pitch responses.

This can be easily proven in smooth air or in a ground training device that has the aerodynamic responses of an airplane. Set up a stabilized 500-fpm descent and decrease power 100 rpm. Note how long it takes for vertical speed to stabilize at approximately 700 fpm. Again, set up a stabilized 500-fpm descent and decrease pitch attitude by half a bar. Note how quickly the vertical speed stabilizes at approximately 700 fpm.

The term half a bar, refers to pitch indications on the attitude indicator. On most light-airplane attitude indicators, the horizontal bars that represent the airplane and the horizon are of equal width. In level flight during cruise, the airplane bar should be adjusted so that it sits directly in front of the horizon bar. If you then decrease pitch so that the top of the airplane bar touches the bottom of the horizon bar, you made a one-bar pitch change. A half-a-bar pitch change is half of that.

Many former U.S. Navy and Marine Corps pilots who have no civilian aviation experience also subscribe to the airspeed-with-pitch-and-altitude or vertical-speed-with-power concept. They flew this way in the military, but they used pitch to control angle of attack (AOA), which is an excellent way to fly if you have an AOA indicator. It is understandable that without an AOA indicator they would assume that pitch is always used to control airspeed. Unfortunately, very few light airplanes have AOA indicators.

So, let's start with a rule that no one can refute. If airspeed is correct, pitch and power must work together when either altitude or vertical speed needs correcting. This is called elevator-throttle coordination, and it is a requirement for proficient instrument flight. If you need to change power for whatever reason, you must simultaneously change pitch in order to maintain airspeed; if you need to change pitch for whatever reason, you must simultaneously change power in order to maintain airspeed.

Finesse is the name of the game when you make these compounded control inputs. A small pitch change combined with a small power change will generate a significant performance change.

Here is the true essence of instrument interpretation: If airspeed is not correct, you must interpret the airspeed and altimeter indications if flying level-or the airspeed and vertical speed indications if climbing or descending-to determine whether a pitch or a power correction will eliminate the deviation. The correct decision will decrease your workload and significantly improve your performance. The table below lists the appropriate initial corrections.

In summary, just remember this: If airspeed is correct, pitch and power must work together. But, if airspeed and altitude or airspeed and vertical speed are incorrect, stop and interpret the two indications before you make an initial control input. If the deviations are small, the correction will require either a pitch or a power change. If, however, the deviations are excessive and you are getting behind the airplane (the airplane is taking you for a ride, and you're almost a passenger), go after airspeed with power and altitude or vertical speed with pitch.

Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying for 43 years and has 25,000 hours in fixed- and rotary-wing aircraft. Visit his Web site.

WANT TO KNOW MORE?

Links to additional resources on instrument flying, and IFR training for VFR pilots, may be found at AOPA Online.