A C182 with a student and instructor pilots aboard suffered a track deviation when both VOR cdis sho...

Narrative:

My instrument student had just completed 3 VOR/DME runway 16 instrument approaches at mcc and the airplane's navigational equipment appeared to function normally. We then proceeded to artey intersection for the VOR/DME runway 22L instrument approach at mather field mhr.after completing the procedure turn and establishing ourselves on the final approach course (intermediate approach segment) we noted that the GPS (garmin 296--used for situational awareness only) depicted us flying south; away from the final approach course. However; both cdis remained centered. This caused me and my student to question the accuracy of the airplane's equipment. I tuned the imhr localizer frequency in navigation two and the CDI indicated that we were south of the localizer. Since we were VFR I contacted mhr tower and canceled our IFR clearance and proceeded to the airport VFR and landed. I notified the tower of our navigational discrepancy and after parking also notified norcal approach control as well just in case there was a problem with the sac VOR. My student and I trouble shot the vors on the ground and could not determine if a problem existed with the airplane or the sac VOR.I also wanted to mention that mhr tower did an excellent job of observing our course divergence and pointing it out to us.

Original NASA ASRS Text

Title: A C182 with a student and instructor pilots aboard suffered a track deviation when both VOR CDIs showed on course inbound on the VOR/DME approach when they were; in fact; tracking south of course. A GPS used primarily for situational awareness provided the initial awareness of the deviation.

Narrative: My instrument student had just completed 3 VOR/DME Runway 16 Instrument Approaches at MCC and the airplane's navigational equipment appeared to function normally. We then proceeded to ARTEY Intersection for the VOR/DME Runway 22L Instrument Approach at Mather Field MHR.After completing the procedure turn and establishing ourselves on the final approach course (intermediate approach segment) we noted that the GPS (Garmin 296--used for situational awareness only) depicted us flying south; away from the final approach course. However; both CDIs remained centered. This caused me and my student to question the accuracy of the airplane's equipment. I tuned the IMHR LOC frequency in NAV Two and the CDI indicated that we were south of the Localizer. Since we were VFR I contacted MHR Tower and canceled our IFR Clearance and proceeded to the airport VFR and landed. I notified the Tower of our navigational discrepancy and after parking also notified NORCAL Approach Control as well just in case there was a problem with the SAC VOR. My student and I trouble shot the VORs on the ground and could not determine if a problem existed with the airplane or the SAC VOR.I also wanted to mention that MHR Tower did an excellent job of observing our course divergence and pointing it out to us.

Data retrieved from NASA's ASRS site as of April 2012 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	925377
Time
Date	201012
Local Time Of Day	1201-1800
Place
Locale Reference	MHR.Airport
State Reference	CA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 17000 Flight Crew Type 200
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Clearance Deviation - Track / Heading All Types

A C182 with a student and instructor pilots aboard suffered a track deviation when both VOR cdis showed on course inbound on the VOR/DME approach when they were; in fact; tracking south of course. A GPS used primarily for situational awareness provided the initial awareness of the deviation.