Why would anyone change to 121.5 to make a mayday call out at NI when they were operating NI radio(or unicom or what whatever its called now?) Why not make it on the frequency which you KNEW was being received locally? And further, if there was little(or no) other traffic operating the frequency I would even dispense with the three repetitions of Mayday and call-sign. One is enough. The meaning is clear. One Mayday, declare emergency, declare intentions.