Why isn't the airspeed indicator the primary instrument for power during a constant speed climb?

Question

I am studying the primary and secondary IFR instrument designations. I understand that the primary instrument is the one that closest represents your target value, and is normally the one gauge that isn't moving on the panel during the targeted maneuver (for example, in a constant rate turn, the Turn Coordinator is stabilized on a value after entry is completed and becomes primary).

I fly a variable pitch prop, and I think my confusion might be a result of not flying a constant speed propeller.

Take a look at the item in red:

Question:

• Can someone explain why the CS Climb power primary isn't the airspeed indicator?

If you are stabilized on your airspeed, wouldn't airspeed dictate the power setting you want to maintain? If you change pitch, the airspeed drops/rises and the power is changed - doesn't that make the airspeed indicator primary? I have been taught to set power (on entry) and then monitor airspeed to make pitch adjustments. This makes the idea of a power primary confusing in stabilized descent/climb.

This seems like a confusing way to have to learn the material as I don't find I have to think about this while flying to effectively control the airplane...

Answer 1

Airspeed indicator is a primary instrument for pitch in that row, so it can't be also primary for power.

The point of constant speed climb is that you select power and maintain speed with pitch, getting whatever climb rate that power can support. Most often the point is selecting "climb" or "maximum continuous" power and climbing as fast as possible without overstressing the engine.

The only difference with variable pitch prop is that it decouples rpm from engine power, so you can't use rpm and are left with manifold pressure only (for piston; I am not sure what the correct reference is for turbine).

Note that two lines lower there is a constant rate climb and there airspeed is primary reference for power, because there you adjust pitch to maintain desired vertical speed and power to maintain airspeed. But since you shouldn't use more power than the recommended climb setting anyway, the constant speed climb gives you better performance.