When an aircraft engine is left running on the ground and no person remains onboard, the aircraft’s movement must be restricted and
Why this is the answer
Under CAR 602.10, an aircraft with its engine running may be left with no one aboard only if its movement is restricted and it is not left unattended — a competent person must be at the controls or monitoring it. Weight limits and control locks (the other options) are not the rule.
Reference
CARs 602.10 – Starting and Ground Running of Aircraft Engines
Question reproduced verbatim from Transport Canada’s PSTAR Study and Reference Guide (TP 11919E). The answer key is Transport Canada’s; the explanation is ours.
A study aid — not a substitute for the official guide, the CARs, or your instructor.