Narrative:

I was asked by a friend (a private pilot who also filled out a NASA form) to fly with him on a flight from lot airport (southwest of chicago) to maine and then returning. My purpose was to be there as insurance, since I am instrument rated and have a CFI. It was agreed prior to flight, that I would only be acting as a CFI or PIC during IMC, marginal WX, night flight, and during any emergency sits. The first flight (lot-izg) was without incident and my friend did very well. On the return flight, I acted as PIC on the first leg (izg to roc) because we ended up flying IFR due to mountain obscurement. During the remainder of the flight, my friend was PIC because the WX was exceptionally good. I was just there for the ride. I had no problem with this because my friend's past performance was excellent. On the last flight segment (fwa-lot) I was resting while my friend flew the airplane. Apparently, my friend naved the airplane from fwa to the chicago heights VOR using VOR, GPS, and pilotage. After crossing the chicago heights VOR, my friend descended to 3000 ft MSL and tracked direct to lot using GPS in order to avoid both chicago's class B airspace and midway's class C airspace. Apparently, the GPS was giving my friend erroneous information, having my friend fly well north of course. While my friend was flying, I happened to glance out the window and noticed what appeared to me to be midway off to the northeast. I questioned my friend on this, and he agreed. It appeared that we were in the airspace. At this point I helped my friend get back on course. We ended up north of lot, and flew south to land without incident. It appeared to me that we may have penetrated both midway's class C airspace and possibly chicago's class B airspace -- just what my friend was trying to avoid. After landing, my friend told me that he thought he was getting conflicting information from the GPS compared to his pilotage. However, he incorrectly chose to follow the GPS. I believe that if he would have communicated this information to me in flight, this entire situation could have been avoided. Callback conversation with reporter revealed the following information: reporter states the aircraft was a rental and it has an installed GPS unit. The aircraft was a PA28 arrow. Reporter was becoming familiar with GPS on this flight and it was a 'learn as you go' operation. The GPS worked very well 99.9% of the time, but twice sent them astray. Once was in maine, where there are few ground based navaids to use for backup so pilotage was used. The second time it gave erroneous information was the incident reported to ASRS. There seemed to be correct waypoint information but the tracking information was incorrect.

Related reports:

Google
 

Original NASA ASRS Text

Title: PA28 ARROW PLT USING GPS NAV HAS POSSIBLE PENETRATION OF AIRSPACE. GPS EQUIP GIVES FALSE TRACING INFO.

Narrative: I WAS ASKED BY A FRIEND (A PVT PLT WHO ALSO FILLED OUT A NASA FORM) TO FLY WITH HIM ON A FLT FROM LOT ARPT (SW OF CHICAGO) TO MAINE AND THEN RETURNING. MY PURPOSE WAS TO BE THERE AS INSURANCE, SINCE I AM INST RATED AND HAVE A CFI. IT WAS AGREED PRIOR TO FLT, THAT I WOULD ONLY BE ACTING AS A CFI OR PIC DURING IMC, MARGINAL WX, NIGHT FLT, AND DURING ANY EMER SITS. THE FIRST FLT (LOT-IZG) WAS WITHOUT INCIDENT AND MY FRIEND DID VERY WELL. ON THE RETURN FLT, I ACTED AS PIC ON THE FIRST LEG (IZG TO ROC) BECAUSE WE ENDED UP FLYING IFR DUE TO MOUNTAIN OBSCUREMENT. DURING THE REMAINDER OF THE FLT, MY FRIEND WAS PIC BECAUSE THE WX WAS EXCEPTIONALLY GOOD. I WAS JUST THERE FOR THE RIDE. I HAD NO PROB WITH THIS BECAUSE MY FRIEND'S PAST PERFORMANCE WAS EXCELLENT. ON THE LAST FLT SEGMENT (FWA-LOT) I WAS RESTING WHILE MY FRIEND FLEW THE AIRPLANE. APPARENTLY, MY FRIEND NAVED THE AIRPLANE FROM FWA TO THE CHICAGO HEIGHTS VOR USING VOR, GPS, AND PILOTAGE. AFTER XING THE CHICAGO HEIGHTS VOR, MY FRIEND DSNDED TO 3000 FT MSL AND TRACKED DIRECT TO LOT USING GPS IN ORDER TO AVOID BOTH CHICAGO'S CLASS B AIRSPACE AND MIDWAY'S CLASS C AIRSPACE. APPARENTLY, THE GPS WAS GIVING MY FRIEND ERRONEOUS INFO, HAVING MY FRIEND FLY WELL N OF COURSE. WHILE MY FRIEND WAS FLYING, I HAPPENED TO GLANCE OUT THE WINDOW AND NOTICED WHAT APPEARED TO ME TO BE MIDWAY OFF TO THE NE. I QUESTIONED MY FRIEND ON THIS, AND HE AGREED. IT APPEARED THAT WE WERE IN THE AIRSPACE. AT THIS POINT I HELPED MY FRIEND GET BACK ON COURSE. WE ENDED UP N OF LOT, AND FLEW S TO LAND WITHOUT INCIDENT. IT APPEARED TO ME THAT WE MAY HAVE PENETRATED BOTH MIDWAY'S CLASS C AIRSPACE AND POSSIBLY CHICAGO'S CLASS B AIRSPACE -- JUST WHAT MY FRIEND WAS TRYING TO AVOID. AFTER LNDG, MY FRIEND TOLD ME THAT HE THOUGHT HE WAS GETTING CONFLICTING INFO FROM THE GPS COMPARED TO HIS PILOTAGE. HOWEVER, HE INCORRECTLY CHOSE TO FOLLOW THE GPS. I BELIEVE THAT IF HE WOULD HAVE COMMUNICATED THIS INFO TO ME IN FLT, THIS ENTIRE SIT COULD HAVE BEEN AVOIDED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THE ACFT WAS A RENTAL AND IT HAS AN INSTALLED GPS UNIT. THE ACFT WAS A PA28 ARROW. RPTR WAS BECOMING FAMILIAR WITH GPS ON THIS FLT AND IT WAS A 'LEARN AS YOU GO' OP. THE GPS WORKED VERY WELL 99.9% OF THE TIME, BUT TWICE SENT THEM ASTRAY. ONCE WAS IN MAINE, WHERE THERE ARE FEW GND BASED NAVAIDS TO USE FOR BACKUP SO PILOTAGE WAS USED. THE SECOND TIME IT GAVE ERRONEOUS INFO WAS THE INCIDENT RPTED TO ASRS. THERE SEEMED TO BE CORRECT WAYPOINT INFO BUT THE TRACKING INFO WAS INCORRECT.

Data retrieved from NASA's ASRS site as of July 2007 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.