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A PA28 pilot with a newly installed transponder flew the transponder pressure altitude instead of the barometrically corrected altimeter.
| Attributes | |
| ACN | 921586 |
| Time | |
| Date | 201011 |
| Local Time Of Day | 0001-0600 |
| Place | |
| Locale Reference | RTS.Airport |
| State Reference | NV |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | PA-28 Cherokee/Archer/Dakota/Pillan/Warrior |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Initial Climb |
| Flight Plan | None |
| Component | |
| Aircraft Component | Transponder |
| Person 1 | |
| Function | Pilot Flying Single Pilot |
| Qualification | Flight Crew Commercial Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 30 Flight Crew Total 5000 Flight Crew Type 500 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Airspace Violation All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance |
Narrative:
I took off and started a spiral climb at night out of rts (reno-stead) after installation of new transponder. While circling up to gain sufficient altitude before flying into the sierras towards truckee; ca; I believe I may have inadvertently crossed into class C airspace for reno international. When I noticed the C airspace on my moving map GPS; I immediately proceeded more northwest-bound to clear that airspace. However; I was probably only below the lateral layer of the C airspace. Then; while trying to learn the workings of the new transponder; I noticed that the transponder was indicating on the display the pressure altitude (or flight levels); not the MSL altitude. Since the barometric pressure was 30.40 to 30.50 in the area; the transponder was reporting about a 400 ft different altitude than at what I was flying as I approached the sacramento area and flew on into the san fransisco bay area. I was not sure which altitude I should be flying; so I flew hemispherical rule altitude based on the transponders fl readout; instead of the altimeter. This meant I was flying 400 ft higher than what the transponder was reporting 6;850 ft baro altitude versus 6;500 pressure altitude. I thought there was something I could do to reset the transponder to the local barometric setting; but couldn't figure out how to do it while flying the airplane. My mistake; I learned later; was ATC radar software converts the pressure altitude that the transponder reports; and converts it to MSL altitude based on local altimeter settings. Nowhere in the transponder's literature does it discuss this. So in effect I was flying IFR altitudes instead of VFR altitudes based on the very high pressure existing in the area at the time. This seems to be very important information that should be placed in the transponder's manual; as well as in the aim and other educational publications. While I was thinking I was flying a correct altitude based on what the transponder was reporting; I was; in fact; a danger to others at their correct flight levels. The fact that ATC radar software correct the reporting PA should be publicized so that pilots know what is going on.
Original NASA ASRS Text
Title: A PA28 pilot with a newly installed transponder flew the transponder pressure altitude instead of the barometrically corrected altimeter.
Narrative: I took off and started a spiral climb at night out of RTS (Reno-Stead) after installation of new transponder. While circling up to gain sufficient altitude before flying into the Sierras towards Truckee; CA; I believe I may have inadvertently crossed into Class C airspace for Reno International. When I noticed the C airspace on my moving map GPS; I immediately proceeded more northwest-bound to clear that airspace. However; I was probably only below the lateral layer of the C airspace. Then; while trying to learn the workings of the new transponder; I noticed that the transponder was indicating on the display the Pressure Altitude (or Flight Levels); not the MSL altitude. Since the barometric pressure was 30.40 to 30.50 in the area; the transponder was reporting about a 400 FT different altitude than at what I was flying as I approached the Sacramento area and flew on into the San Fransisco Bay Area. I was not sure which altitude I should be flying; so I flew hemispherical rule altitude based on the transponders FL readout; instead of the altimeter. This meant I was flying 400 FT higher than what the transponder was reporting 6;850 FT baro altitude versus 6;500 pressure altitude. I thought there was something I could do to reset the transponder to the local barometric setting; but couldn't figure out how to do it while flying the airplane. My mistake; I learned later; was ATC radar software converts the pressure altitude that the transponder reports; and converts it to MSL altitude based on local altimeter settings. Nowhere in the transponder's literature does it discuss this. So in effect I was flying IFR altitudes instead of VFR altitudes based on the very high pressure existing in the area at the time. This seems to be very important information that should be placed in the transponder's manual; as well as in the AIM and other educational publications. While I was thinking I was flying a correct altitude based on what the transponder was reporting; I was; in fact; a danger to others at their correct flight levels. The fact that ATC radar software correct the reporting PA should be publicized so that pilots know what is going on.
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.