How do planes descend for landing? I fly occasionally  on a pretty short route on a turboprop (DHC-8). When the airplane descends for landing, I can look through the window and see the ground below getting closer over time. However I can't really tell what the pilots do to achieve that. I know that turns make you lose altitude, but it's very clear to me when the airplane makes a turn, so let's count that one out. So we're basically left with:


Slight nose-down attitude
Reduction of engine power
Combination of both


The reason I'm asking this is that during descent I do get this sensation of going down. However, during that time I cannot really see what the pilot did to achieve it. The nose-down attitude might be too minor for me to actually notice (I do not notice a slight nose-up cruising attitude to be honest). I hear a slight reduction in engine power a few times during a descent, but the feeling of going down and the audible noise reduction are separated in time. Is it that it takes time for an airplane to reduce speed (and as a result, descend) when you reduce engine power?

One additional question: I guess that with all the electronics in the cockpit pilots just set a target altitude or rate of descent, and then the airplane systems apply the correct measures to achieve this. How does the airplane know how much to reduce engine power and/or pitch to achieve this exact rate of descent?
If the pilot reduces the airspeed while he increases the rate of descent, you will not notice any change in pitch attitude when the aircraft descends. With jets you should be able to hear a change in engine pitch when thrust is reduced. Turboprops run their engines at constant speed, and a reduction in power here means a reduction in propeller pitch. This causes the propeller noise to change, but this change is harder to discern. With a little practice you should be able to hear the slight drop in propeller noise which signals the begin of the descent, though.

Gliders control their sink rate by flying in rising or sinking air, and additionally by flying slow (and near their minimum sink rate) or fast. To descend quickly, they can open speed brakes and/or sideslip. My favorite for a fast descent is to spin the aircraft, but airliners do not use this option.

In order to produce the necessary lift to keep the aircraft in the air, the pilot picks a combination of speed and angle of attack at which lift equals weight. Other combinations would result in an accelerating vertical speed and are only used in transitions from one flight state to the next.

To arrive at the aircraft's pitch attitude, you need to add the flight path angle to this angle of attack. If the plane descends with a flight path angle of -3° and the pilot reduces speed such that he needs to increase the angle of attack by the same 3° to produce the same lift, the resulting pitch angle of the aircraft would stay the same.

Normally, the correct answer to your question is 2. Reduction of engine power. But the other answers are also correct: If the speed is held constant, the attitude has to be reduced by the desired flight path angle change. Note that this is achieved by reducing thrust alone. If the pilot wishes to descend really fast, he might move to answer 3. Combination of both as in this answer.