ACR LTT CREW PERFORMS 2 TKOF ATTEMPTS AND 2 ABORTED TKOFS.

Narrative

WE WERE GETTING A LINE CHK FROM AN FAA EXAMINER WHICH WAS IN THE JUMP SEAT; FROM PIT TO JHW. AFTER COMPLETING THE BEFORE START CHKLIST; AFTER START CHKLIST; WE OBTAINED A TAXI CLRNC AND TAXIED TO THE ACTIVE RWY. WHILE TAXIING WE COMPLETED THE TAXI CHKLIST AND NOW WE WERE #1 FOR TKOF. WHEN WE WERE CLRED ONTO THE RWY FOR TKOF; WE COMPLETED THE LINE-UP CHKLIST AND WERE READY FOR DEP. THEN THE CAPT ADDED PWR AND WE WERE ROLLING DOWN THE RWY WHEN A WARNING HORN SOUNDED. THE CAPT IMMEDIATELY VERIFIED THAT THE CONDITIONS WERE FORWARD; WHICH THEY WERE; AND THAT THE FLAPS WERE UP; AND THEY WERE; AND THAT THE TRIM WAS IN THE GREEN ARC FOR TKOF; WHICH IT WASN'T. THEREFORE; THE CAPT ABORTED THE TKOF AND WE TAXIED CLR OF THE RWY. THE CAPT RESET THE TRIM TO AN APPROPRIATE TKOF POS AND WE TAXIED BACK TO THE ACTIVE RWY FOR DEP. WHEN TAXIING BACK WE ENCOUNTERED A HDG COMPARATOR WARNING LIGHT WHICH WE WERE ABLE TO RESET AND EXTINGUISH THE WARNING LIGHT. THIS HAPPENED TWICE. WE COMPLETED ALL THE APPROPRIATE CHKLISTS AND AGAIN WE WERE CLRED FOR TKOF. ON TKOF THE HDG COMPARATOR WARNING LIGHT ILLUMINATED AGAIN SO THE CAPT ABORTED THE TKOF AND TAXIED BACK TO THE GATE. MAINT WAS CALLED AND IT WAS DETERMINED THAT ONE OF THE ACFT'S COMPUTERS HAD A PROB AND WAS GNDED. THE FLT WAS CANCELED. NOTE: THAT NEW CHKLISTS WERE MADE TO IMPROVE THE FLOW OF THE PREVIOUS ONES; AND WERE ONLY IMPLEMENTED A FEW DAYS PRIOR TO THIS.