Three deadlines, each tied to a signal.
27.1
By the warning signal: signal the course if the sailing instructions have not fixed it (and swap one course signal for another), and require personal flotation devices with flag Y and one sound.
27.2
By the preparatory signal: move a starting mark. After that the line is fixed for that start.
27.3
Up to the starting signal, for any reason: postpone (AP, AP over H, AP over A, two sounds) or abandon (N, N over H, N over A, three sounds).
Changed in 2025
Flag N is now listed among the signals available before the starting signal.