Narrative:

I was being vectored by atlanta departure control during a climb to an assigned altitude of 11000 ft. The departure SID is in essence 'radar vectors on course.' the controller was attempting to vector me to join a jet airway. She made a couple of attempts by adding 10 or 15 degrees at each attempt instead of just saying 'join jxx on course.' when I realized she was having a problem picking an intercept angle that would work, I started looking at the map to calculate an intercept that would allow me to join the jet airway. I was using the autoplt to hold heading and climb attitude, but I did not have the altitude preselect armed for capture. I was IMC and monitoring my instruments while looking at the map. I have an xx model transponder that displays the mode C altitude that is being transmitted. I was using looking at the mode C display as an easy way to quickly check my altitude in the climb. When I noticed I was approaching 11000 ft I crosschecked with my altimeter and realized I was passing through 11400 ft. I immediately disconnected the autoplt and started a descent. I descended approximately 100 ft before the controller called and cleared me for a new climb to a higher altitude. She said nothing of the discrepancy between my altimeter and what was being displayed on the mode C display. The total time between starting to look at the map and climbing through 11000 ft was approximately 2 mins. After landing I read the sales and operating literature on the transponder and found out that it is preset to 29.92 inch hg and may only display the actual altitude above FL180 when I reset my altimeter. I have also learned that the computers on the ground that interpret the mode C compensate for this discrepancy automatically. I completed my factory initial training for this aircraft only a couple of weeks prior, with no mention of this as a potential consideration. As a new pilot into the flight levels, it would have been helpful to know this information. I realize that the altimeter is my primary source of altitude reference but in a new airplane flying single pilot IFR in IMC with a controller that seemed unsure of what she was doing, interrupting the altimeter during the climb seemed harder than looking at a digital display.

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Original NASA ASRS Text

Title: SMA PLT IMC EXCEEDS ASSIGNED ALT.

Narrative: I WAS BEING VECTORED BY ATLANTA DEP CTL DURING A CLB TO AN ASSIGNED ALT OF 11000 FT. THE DEP SID IS IN ESSENCE 'RADAR VECTORS ON COURSE.' THE CTLR WAS ATTEMPTING TO VECTOR ME TO JOIN A JET AIRWAY. SHE MADE A COUPLE OF ATTEMPTS BY ADDING 10 OR 15 DEGS AT EACH ATTEMPT INSTEAD OF JUST SAYING 'JOIN JXX ON COURSE.' WHEN I REALIZED SHE WAS HAVING A PROBLEM PICKING AN INTERCEPT ANGLE THAT WOULD WORK, I STARTED LOOKING AT THE MAP TO CALCULATE AN INTERCEPT THAT WOULD ALLOW ME TO JOIN THE JET AIRWAY. I WAS USING THE AUTOPLT TO HOLD HDG AND CLB ATTITUDE, BUT I DID NOT HAVE THE ALT PRESELECT ARMED FOR CAPTURE. I WAS IMC AND MONITORING MY INSTS WHILE LOOKING AT THE MAP. I HAVE AN XX MODEL TRANSPONDER THAT DISPLAYS THE MODE C ALT THAT IS BEING XMITTED. I WAS USING LOOKING AT THE MODE C DISPLAY AS AN EASY WAY TO QUICKLY CHK MY ALT IN THE CLB. WHEN I NOTICED I WAS APCHING 11000 FT I XCHKED WITH MY ALTIMETER AND REALIZED I WAS PASSING THROUGH 11400 FT. I IMMEDIATELY DISCONNECTED THE AUTOPLT AND STARTED A DSCNT. I DSNDED APPROX 100 FT BEFORE THE CTLR CALLED AND CLRED ME FOR A NEW CLB TO A HIGHER ALT. SHE SAID NOTHING OF THE DISCREPANCY BTWN MY ALTIMETER AND WHAT WAS BEING DISPLAYED ON THE MODE C DISPLAY. THE TOTAL TIME BTWN STARTING TO LOOK AT THE MAP AND CLBING THROUGH 11000 FT WAS APPROX 2 MINS. AFTER LNDG I READ THE SALES AND OPERATING LITERATURE ON THE TRANSPONDER AND FOUND OUT THAT IT IS PRESET TO 29.92 INCH HG AND MAY ONLY DISPLAY THE ACTUAL ALT ABOVE FL180 WHEN I RESET MY ALTIMETER. I HAVE ALSO LEARNED THAT THE COMPUTERS ON THE GND THAT INTERPRET THE MODE C COMPENSATE FOR THIS DISCREPANCY AUTOMATICALLY. I COMPLETED MY FACTORY INITIAL TRAINING FOR THIS ACFT ONLY A COUPLE OF WKS PRIOR, WITH NO MENTION OF THIS AS A POTENTIAL CONSIDERATION. AS A NEW PLT INTO THE FLT LEVELS, IT WOULD HAVE BEEN HELPFUL TO KNOW THIS INFO. I REALIZE THAT THE ALTIMETER IS MY PRIMARY SOURCE OF ALT REF BUT IN A NEW AIRPLANE FLYING SINGLE PLT IFR IN IMC WITH A CTLR THAT SEEMED UNSURE OF WHAT SHE WAS DOING, INTERRUPTING THE ALTIMETER DURING THE CLB SEEMED HARDER THAN LOOKING AT A DIGITAL DISPLAY.

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.