Bonanza 36
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 20; Flight Crew Total 2200; Flight Crew Type 2000
Confusion
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem
Aircraft
This was a personal IFR flight with landing airport conditions approximately 2;000 FT overcast; with good visibility. Winds favored Runway 10. Conditions deteriorated slightly too about 1;900 FT overcast as I approached the area and upon being turned over to ATC Approach by the Center Controller. Because the airport was MVFR; I elected to fly the VOR approach; and was vectored onto the approach course just outside of [the final approach fix]. I noted that the aircraft had drifted south of course; likely because of a stronger southerly wind than anticipated. As I corrected; ATC advised that I was south of course; but noted that I was correcting. However; I noted disagreement among instruments as to precise course: The VOR indicator indicated that I was on course; the GPS moving map showed me slightly south of course; and the handheld iPad with geo-referenced approach flight through Foreflight also showed me slightly south of course. As indicated above; I corrected my course and at approximately that point entered VFR conditions. At that point; I proceeded visually and canceled my IFR flight plan. The problem in question was not severe; because I was very familiar with the area; the approach; and my specific location. However; the disagreement among instruments was confusing; particularly since it was my understanding that the VOR indicator was primary. However; I later learned upon testing the indicator that it; rather than the geo-referenced approach plate and GPS moving map; was erroneous. Moving maps offer wonderful situational awareness; but confusion results when various indicators disagree as to position. Frequent cross-checking in good VFR conditions is necessary in order to verify that all are accurate and to correct any inaccuracies or disagreements that might exist.
The pilot of a Beech 36 observed a disagreement in his instruments during an IFR approach. He later confirmed that the VOR indicator was incorrect; even though it is recognized as the primary instrument.