A typical small unmanned aircraft under Part 107 does not go through a Part 91 annual inspection. Section 107.15 is the rule that replaces that picture: no person may operate the aircraft unless it is in a condition for safe operation, and the remote pilot in command must check it before each flight. Scheduled maintenance follows intervals the manufacturer sets. A hard landing starts unscheduled maintenance, and the next flight waits until that problem is corrected.
Condition for safe operation, before every flight
Section 107.15(a) has two sentences that the test treats as one idea. The aircraft may not be operated unless it is in a condition for safe operation. Prior to each flight, the remote pilot in command must check the system to determine whether it is in that condition. Paragraph (b) adds that no person may continue a flight once they know, or have reason to know, that the system is no longer safe.
That check is the remote pilot's, every flight. It is not an annual sign-off by a certificated mechanic, and registration does not make an unsafe aircraft legal to fly. The ACS maintenance item you are assigned cites AC 107-2A paragraph 7.2.2 for the case where preflight finds a need for unscheduled repair, including after a mishap: flight operations should not occur until the issue is corrected. Section 107.15 is the regulation that sits beside that paragraph. "It looks minor and the battery still has a charge" is not the correction. "We will fix it at the next scheduled interval" leaves the aircraft outside a condition for safe operation on purpose.
Who may do the work, for a typical Part 107 aircraft, is the remote pilot or owner following the manufacturer's instructions. Part 107 does not require an FAA-certificated mechanic for that ordinary maintenance. Follow the manual. If the manufacturer, or a rule that applies because the aircraft is being operated under a tighter regime, says someone else must do the work, follow that instruction. Category 4 is the clear example. Section 107.140 requires an airworthiness certificate under part 21 and requires maintenance, preventive maintenance, alterations, and inspections to be done as that section specifies, using the methods in the manufacturer's maintenance manual or Instructions for Continued Airworthiness, or other methods acceptable to the Administrator. A Category 4 aircraft is not "the remote pilot tightens whatever they like." A typical Part 107 quadcopter with no airworthiness certificate is not Category 4, and it does not inherit a Part 91 annual.
The preflight actions in §107.49, including control links and available power, are the operational check that sits next to maintenance. They are covered on the preflight familiarization page. The safe-condition rule itself is the condition for safe operation page.
Scheduled work follows the manufacturer
Scheduled maintenance is maintenance performed at intervals the manufacturer sets: hours, cycles, or calendar time. Propeller replacement at a cycle count, a battery retirement date, and a firmware or hardware interval in the manual are the pattern. The work is not prohibited by Part 107, and it is not something the FAA has to come out and perform.
The interval is the manufacturer's, not an interval you invent to match manned-aircraft tradition. If the manual says 200 cycles, the 200th cycle is the schedule. If the manual is silent, you still have §107.15. Silence in a manual is not permission to fly a cracked arm.
A hard landing is unscheduled
Unscheduled maintenance is the inspection and any repairs that follow a problem you discover. The question uses a hard landing. The inspection and the repairs are unscheduled maintenance. They are not the scheduled program, and they are not an annual inspection. The explanation's phrase is "problem-triggered."
The ACS scenario is the same idea with a sharper stop. During preflight the remote pilot finds a component that needs repair after a mishap, and the finding is outside the manufacturer's scheduled interval. The keyed action is that flight operations should not occur until the issue is corrected. Postponing the repair until the next scheduled interval is the wrong choice. Flying because the damage "looks minor" is the other wrong choice.
Write down what you found and what you did. Part 107 does not create one universal logbook retention period for every small UAS. Category 4 has specific record duties in §107.140. A useful record still helps you show what was wrong and when it was fixed, which is the fact §107.15 cares about: the aircraft is back in a condition for safe operation.
After the grass landing
A gust drops the aircraft onto the grass at the end of a mapping flight. You do not relaunch on the next battery. The hard landing is the trigger for unscheduled maintenance. You inspect the arms, the props, the motors, and the battery for damage the manual tells you to look for. You find a split propeller. That part needs repair, the need showed up outside any hour or cycle interval, and AC 107-2A paragraph 7.2.2 says you do not fly until it is corrected. You replace the propeller using the manufacturer's instructions, confirm the aircraft is in a condition for safe operation, and only then consider another flight. The Category 4 path would add the airworthiness and maintenance-manual duties if this aircraft were in that category. This one is not.
Next month the manual's calendar item comes due: a scheduled inspection at the interval the manufacturer published. That one is scheduled. The split propeller was not. Keeping the two labels straight is the terminology item. Refusing to fly the broken propeller is the scenario item.
The trap
The scheduled-maintenance trap says the work is prohibited, or that the FAA must perform it. The keyed description is manufacturer intervals: hours, cycles, or calendar time.
The hard-landing trap offers "scheduled" or "annual." Problem-triggered work is unscheduled. There is no Part 91 annual hiding in §107.15.
The ACS trap offers a launch with minor-looking damage, or a delay until the next scheduled interval. Flight operations wait until the issue is corrected. Section 107.15 is the regulation. Paragraph 7.2.2 of AC 107-2A is the paragraph the question cites.
Practice the maintenance items on the free practice test. The inspection lessons in the course separate the every-flight condition check from the manufacturer's intervals.