The pilot of a beech 36 observed a disagreement in his instruments during an IFR approach. He later ...

Narrative:

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.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1102478
Time
Date	201307
Local Time Of Day	0601-1200
Place
Locale Reference	GKT.Airport
State Reference	TN
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Bonanza 36
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	ILS/VOR
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Commercial Flight Crew Instrument
Experience	Flight Crew Last 90 Days 20 Flight Crew Total 2200 Flight Crew Type 2000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

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.