US-FAA14 CFR 107.15
Condition for safe operation
Read the official ruleOfficial FAA regulation text (public domain)
(a) No person may operate a civil small unmanned aircraft system unless it is in a condition for safe operation. Prior to each flight, the remote pilot in command must check the small unmanned aircraft system to determine whether it is in a condition for safe operation. (b) No person may continue flight of the small unmanned aircraft when he or she knows or has reason to know that the small unmanned aircraft system is no longer in a condition for safe operation.
Verbatim text of a US Federal Aviation Regulation (public domain), reproduced for reference — not legal advice and not for navigation. A plain-English explainer may be added later; always rely on the current official rule linked above.