Gear or flap malfunctions

Your C172 can't raise its landing gear, so this element splits cleanly in two: a gear concept you should understand for the airplanes in your future, and a flap problem you might actually fly home tomorrow.

Gear: a concept, not a C172 drill

The C172S is fixed-gear — there is no gear malfunction to have, and no gear procedure to fly. But the knowledge area expects you to understand the idea, because the airplanes you transition into later (IX.B's complex aircraft, your eventual checkout) will have retractable gear. So treat this as concept, explicitly not a C172 task:

• A gear malfunction shows up as an unsafe or disagreeing indication — a gear-down light that won't illuminate, a position indicator that disagrees with the handle.
• The response is an emergency extension, and the method is type-specific: a hand crank, a CO₂ or nitrogen blow-down bottle, or a gravity free-fall (sometimes aided by yawing the airplane) that lets the gear drop and lock. The POH for that airplane is the authority.
• Confirm down-and-locked by the indication, and if doubt remains, by a tower fly-by for a visual check before committing to land.

That's the whole gear story for a PP applicant in a 172: know that the failure mode is an indication problem, that there's a manual backup, and that the procedure depends entirely on the type. Don't over-invest here.

Flaps: the malfunction you'll really meet

The flap failure is the one with teeth in a 172, because the flaps are electric and can fail in ways that change how the airplane flies. Three cases:

• Asymmetric / split flap — one flap extends and the other doesn't. This produces a strong roll toward the side with less flap, and it can be powerful. Counter with aileron, stop moving the flaps (don't chase it by cycling the switch), and fly the approach at the higher speed the partial configuration needs. Plan a longer, flatter, faster arrival and don't force a normal touchdown.
• Stuck up (flaps won't deploy) — a flatter, faster, longer approach. With no flaps, your approach speed is higher and float is greater, so pick a longer runway, carry the speed honestly to the flare, and accept the extra distance rather than forcing it down.
• Stuck down (flaps won't retract) — extra drag that won't go away. Carry a little more power to hold the glidepath, expect reduced climb performance on any go-around, and fly the steeper, draggier path deliberately.

A flap motor that simply won't run is frequently an electrical problem — a popped breaker or a charging failure — which loops straight back to K1. The handling response to all of this (counter the roll, re-plan the landing, hit your speeds) is the skill in S1; the knowledge here is just what each failure does to the airplane.