In reply to Welsh Kate:
Definately a Sea King. I couldn't see exactly what was going on but it didn't look like a training exercise. It flew in from the Brecon direction, over the pass below Cribin and down towards the ridge, where it homed in on one particular spot - I assumed they'd found a casualty. I could see someone on the ridge directly above the spot where the Sea King was hovering. It stayed for about 10 minutes and then took off over the ridge towards Storey Arms.