What was found
ABOUT 3 HRS INTO FLT, THE A/T LIM ANNUNCIATED ABOVE ENGINE CLUSTER, VNAV DISCONNECTED. IAW PREVIOUS WRITE UP LOG PAGE 12089346 JUST AFTER BEGINNING DESCENT A/T LIM WENT AWAY. FMC RETURNED TO NORMAL. VNAV AVAILABLE. GROUNDED - YES. PERFORMED BOTH LEFT AND RIGHT HAND FMC BITE PROCEDURE IAWFIM 34-61 TASK 801. FOUND INFLIGHT FAULT. BOTH IRS HAVE TAT- REASON PERFORMED FIM 34-61 TASK 824 ALSO FIM 34-21 TASK 801 IRS BITE TEST, NO CURRENT FAULTS.