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IFR Lesson Guides - Power Control

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Three phases of an instrument rating A widely accepted method of teaching instrument approaches includes the following power-performance model.  To assist you in your instrument training, learn the power settings for each of these phases of flight.  Once you become familiar with the performance of the aircraft, it becomes easier to fly approaches.

1. Effect of Power Changes 

a. In level flight, increase power and point out that the nose has a tendency to rise and yaw left. Hold forward elevator pressure to maintain level flight and relieve the pressure with trim. The position of the ball indicates the need for rudder trim. 
b. In level flight, reduce power and point out that the nose has a tendency to drop and yaw right. Hold back pressure to maintain level flight. The position of the ball indicates the need for rudder trim. 
c. Increase and decrease power, demonstrating that little banking tendency exists if proper rudder pressure and trim are applied. 
d. Student practice. Make large power changes and have the student practice trim control in straight-and-level flight. 
2. Airspeed Changes  -  The terms Low Cruise, Normal Cruise, and High Cruise used in this section refer to speeds which can be established for an airplane used in instrument training or during actual instrument flight. Normal Cruise and High Cruise are enroute speeds. Low Cruise is maintained during holding patterns and the approach phase of an instrument flight. Airspeed changes should be practiced first in a "clean" configuration, then as proficiency increases, while extending the flaps and landing gear. Some of the performance figures and approximate pitch attitudes for a representative general aviation single-engine-airplane follow: 
 

MP RPM IAS Pitch
High Cruise 23 2300 160 1/2 bar low
Normal Cruise 21 2300 140 level
Low Cruise 17 2300 110 1/2 bar high 
500 FPM Climb 23 2500 110 2 bars high 
500 FPM Descent 13 2500 110 1/2 bar low
Low Cruise - Gear Down 22 2500 110 1/2 bar high 
500 FPM Climb - Gear Down 22 2500 110 2 bars high
500 FPM Descent - Gear Down 15 2500 110 1/2 bar low
a. Decrease airspeed - from High Cruise to Normal Cruise or from High Cruise or Normal Cruise to Low Cruise. 
(1) Reduce manifold pressure 3 to 5 inches (or 200 to 300 RPM on an aircraft with a fixed pitch propeller) below power required for desired cruise. Stress smooth and accurate throttle movement in all power changes. When the throttle is moved to the approximate correct position, the manifold pressure gauge is included in the cross-check and a final adjustment made. Re-emphasize the need for proper rudder and elevator trim. 
(2) Pitch must be changed to maintain a constant altitude as airspeed changes. Remind student of acceleration and deceleration errors of the attitude indicator. 
(3) The manifold pressure gauge is the primary power instrument while the airspeed is changing. As the airspeed approaches desired cruise, the airspeed indicator becomes primary for power. Power should then be increased to the approximate setting that will maintain desired cruise airspeed. 

b. Increase airspeed - from Slow Cruise to Normal Cruise or High Cruise, or from Normal Cruise to High Cruise. Increase power 3 to 5 inches (or 200 to 300 RPM on an aircraft with a fixed pitch propeller) above the power required to maintain desired cruise. Trim. The manifold pressure gauge is primary for power while the airspeed is changing. As desired cruise airspeed is approached, the airspeed indicator becomes primary for power and the manifold pressure is adjusted to maintain it. Trim. 

3. Control of Altitude and Airspeed in Straight-and-Level Flight 
a. Altitude is maintained with pitch control and airspeed is maintained with power control. The need for a pitch or power change is indicated by a cross-check between the altimeter and the airspeed indicator. 
b. If the altitude is correct and the airspeed is either high or low, change power to attain the desired airspeed. When the altitude is low and the airspeed is high (or when the altitude is high and the airspeed is low), only a pitch change may be needed to attain the desired altitude and airspeed. When both altitude and airspeed are high or low, a change in both pitch and power is needed. 
4. Interpretation and Cross-Check of Pitch, Bank, and Power Instruments in Straight-and-Level Flight

a. The altimeter is primary for pitch; the heading indicator (or magnetic compass, if the heading indicator is not available) is primary for bank; and the airspeed indicator is primary for power control. During power changes, your cross-check must be particularly efficient and accurate.  b. Student practice changing airspeed in straight-and-level flight: 
(1) With all available pitch, bank, and power instruments. 
(2) Without the heading indicator. 
(3) Without the heading indicator and attitude indicator.


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