What was found
NR 1 BLEED TRIP OFF ILLUMINATED 5 MINUTES AFTER LEVELING OFF AT FL 410. TRIP RESET IAW QRH. DESCENDED TO FL 370, 5 MINUTES AFTER LEVEL OFF, NR 1 BLEED TRIP OFF ILLUMINATED AGAIN. ONCE AGAIN RESET IAW QRH. BOTH TIMES PRESSURIZATION REMAINED AT CRUSING ALT OR 8000 FT ON 1 PACK. NO EXCESS TEMP NOTED ON SUPPLY DUCT TEMP GUAGE. ACFT GROUNDED. PERFORMED BLEED TRIP OFF LIGHT FAULT ISOLATION IAW FIM TASK 36-10, TASK 801. GROUND VERIFIED NR 1 ENGINE BLEED AIR COMPONENTS OPS CHECK GOOD. R & R BLEED AIR REGULATOR, OPS CHECK GOOD IAW AMM 36-11-03, NR 1 ENG BLEED AIR TRIP LIGHT EXTINGUISHED.