16C4 A
 A "Distress Hot Key" VHF DSC Distress alert:
A. Always goes out on the DSC frequency of Ch-70 to alert other stations.
B. Must go out on Ch-16 and Ch-70 to indicate "MAYDAY" traffic will follow.  
C. Must go out on Ch-16 to alert the nearest vessels and coast stations of imminent "MAYDAY" traffic.
D. May go out on Ch-70 or Ch-16 depending on the manufacturer. 
