What was found
INVERTER FAILURE MASTER CAUTION & FLASHING INDICATORS ILLUMINATED 3 DAYS IN A ROW. AFTER FIRST FAILURE PERFORMED OPERATION TEST OF INVERTERS UNDER CART & UNDER ENG POWER. NO DEFECTS SAME FAILURE THE NEXT DAY 15 MIN INTO FLIGHT. FOUND AUXILIARY CONNECTOR LOOSE. AFTER REINSTALLING CONNECTOR, INVERTERS CHECKED GOOD. AGAIN THE SAME FAILURE ON THE NEXT DAY 90 MIN INTO FLIGHT. R & R 115 VOLT AC INVERTER SELECT RELAY.