When should an arm signal be used as a non-pyrotechnic VDS?

An arm signal should be used as a non-pyrotechnic Visual Distress Signal (VDS) when no other distress signals are available. This is because arm signals can effectively communicate distress to nearby vessels or individuals, even in the absence of more conventional signals such as flares or flags. The use of an arm signal is particularly valuable in situations where immediate assistance is needed and alternative methods are either unavailable or impractical.

Other contexts, such as nighttime use, inclement weather, or specific water conditions like shallow waters, may affect the visibility and effectiveness of distress signals, but they do not negate the primary guideline that arm signals serve as a backup when standard distress-signal options are lacking. In essence, the key function of an arm signal is to provide a simple and immediate way to indicate distress when more formal signals are not at hand.