BE35 pilot is advised by ATC to have his compass checked after landing. It is found that the glaresh...

Attributes
ACN	1111155
Time
Date	201308
Local Time Of Day	1201-1800
Place
Locale Reference	DAY.Airport
State Reference	OH
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	Bonanza 35
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Vectors Direct
Flight Plan	IFR
Component
Aircraft Component	Compass (HSI/ETC)
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine Flight Crew Commercial
Experience	Flight Crew Last 90 Days 144 Flight Crew Total 4791 Flight Crew Type 2000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

Columbus approach put me on vectors for the ILS 24L. Vectors were intended to align aircraft with zambo IAF. Before handing me over to dayton tower; columbus approach mentioned that I should check my compass for deviations as he noticed my compass headings being off by about 30 degrees; requiring him to make several adjustments. On the ground I investigated the cause of the deviation and found that the garmin 496 GPS unit (on glareshield with bean-bag mount) I had used on this flight was close enough to the compass to cause this deviation. When removed; the compass worked accurately as per my compass deviation card. There was no hazard in this instance but I am making this report so that others can benefit from this observation that a glareshield mounted portable GPS unit may in fact cause the compass to show a deviated heading.

Original NASA ASRS Text

Title: BE35 pilot is advised by ATC to have his compass checked after landing. It is found that the glareshield mounted Garmin 496 causes a 30 degree compass deviation.

Narrative: Columbus approach put me on vectors for the ILS 24L. Vectors were intended to align aircraft with ZAMBO IAF. Before handing me over to Dayton Tower; Columbus Approach mentioned that I should check my compass for deviations as he noticed my compass headings being off by about 30 degrees; requiring him to make several adjustments. On the ground I investigated the cause of the deviation and found that the Garmin 496 GPS unit (on glareshield with bean-bag mount) I had used on this flight was close enough to the compass to cause this deviation. When removed; the compass worked accurately as per my compass deviation card. There was no hazard in this instance but I am making this report so that others can benefit from this observation that a glareshield mounted portable GPS unit may in fact cause the compass to show a deviated heading.

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.

BE35 pilot is advised by ATC to have his compass checked after landing. It is found that the glareshield mounted garmin 496 causes a 30 degree compass deviation.