Chancellor 414A / C414
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 26000; Flight Crew Type 60
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance; Flight Crew Became Reoriented; General Maintenance Action
Aircraft
IFR clearance received from Miami Center: Direct to Freeport VOR (ZFP) BR63V to MRLIN Intersection; etc. Maintain 8;000 FT. Told to report over ZFP VOR (MIA Center radar coverage is spotty in the vicinity of ZFP VOR). While proceeding to ZFP using GPS the GPS set unlocked (lost signal). I determined my location as 7 miles south of ZFP VOR and was about to call ATC and advise them of our location when ATC called me and advised that I was 7 miles south of ZFP instead of over ZFP as cleared. My apologies were made to ATC and he gave me a 325 degree heading to intercept BR63V westbound out of ZFP and shortly thereafter a clearance direct to MRLIN Intersection. Rest of flight was flown as cleared. Problem was caused by a very weak warning light on the GPS unit that is almost impossible to see in the bright light of a daytime flight. Avionics man is checking out the GPS problem.
C414 pilot experiences GPS failure while navigating direct ZFP at 8;000 FT resulting in a navigational error that is detected by ATC. The GPS failure warning light was on but too faint to be seen readily in the bright daylight.