Coastguard helicopters in the UK use two callsigns, “RESCUE” and “COASTGUARD”. The one they use depends on what they are doing at the time.

  • “RESCUE” is used when they are on a real emergency callout. Your flight tracking app may display this callsign as SRG

  • “COASTGUARD” is used for non emergency operations, like a training exercise or a repositioning flight. Your flight tracking app may display this callsign as SRD

The callsign will then be followed by a 3 digit number, which refers to the base that aircraft is operating from. Each Coastguard base has its own number. For example, Prestwick uses 199. So when there’s an emergency one of the fells in the Lake District and they call in SAR support from Prestwick, the heli will deploy with the callsign RESCUE 199.

When you watch OpenADSB long enough you will start seeing times where a Coastguard heli on a training or routine flight gets caled into action. The SRD will suddenly change to SRG along with a drastic change in course and speed.