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Small aircraft flying VFR below the TCA, advised by tower he had penetrated the TCA at 2300 ft. Was maintaining 1500 ft at all times. Found 600 ft error in transponder.
| Attributes | |
| ACN | 345890 |
| Time | |
| Date | 199608 |
| Day | Wed |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : sea |
| State Reference | WA |
| Altitude | msl bound lower : 1700 msl bound upper : 1750 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : sea tower : bfi |
| Operator | general aviation : personal |
| Make Model Name | Other |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other |
| Route In Use | approach : visual |
| Flight Plan | VFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : single pilot |
| Qualification | pilot : private |
| Experience | flight time last 90 days : 59 flight time total : 469 flight time type : 405 |
| ASRS Report | 345890 |
| Person 2 | |
| Affiliation | government : faa |
| Function | controller : local |
| Qualification | controller : non radar |
| Events | |
| Anomaly | aircraft equipment problem : less severe other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | none taken : unable |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
Each day from may to present date, aug/xx, have travelled same route, same altitude 1700 ft. Altimeter set on departure field elevation and verified again on arrival at destination field. This day, bfi tower called to 'the wbound plane 1-2 mi north of the space needle, are you monitoring this frequency?' my exact position was above the north end of lake union at 1750 ft, 1 1/2 NM north of the needle. The controller told me to 'descend immediately' and asked for my tail number. When my altimeter indicated 1200 ft she told me she had me at 1800 ft and that 2 1/2 mi back I had been at 2300 ft in the bravo space. My encoder was 600 ft in error. At 1200 ft I was nearly level with the 1014 ft radio towers off my left wingtip. I am getting my encoder calibrated/repaired. There was no intrusion into bravo airspace, however, the mode C was reporting 600 ft higher than actual. I immediately verified a problem by connecting a LORAN readout to the mode C output once at home airport. The error on the ground was also 600 ft. The unit will be repaired before further flight.
Original NASA ASRS Text
Title: SMA FLYING VFR BELOW THE TCA, ADVISED BY TWR HE HAD PENETRATED THE TCA AT 2300 FT. WAS MAINTAINING 1500 FT AT ALL TIMES. FOUND 600 FT ERROR IN XPONDER.
Narrative: EACH DAY FROM MAY TO PRESENT DATE, AUG/XX, HAVE TRAVELLED SAME RTE, SAME ALT 1700 FT. ALTIMETER SET ON DEP FIELD ELEVATION AND VERIFIED AGAIN ON ARR AT DEST FIELD. THIS DAY, BFI TWR CALLED TO 'THE WBOUND PLANE 1-2 MI N OF THE SPACE NEEDLE, ARE YOU MONITORING THIS FREQ?' MY EXACT POS WAS ABOVE THE N END OF LAKE UNION AT 1750 FT, 1 1/2 NM N OF THE NEEDLE. THE CTLR TOLD ME TO 'DSND IMMEDIATELY' AND ASKED FOR MY TAIL NUMBER. WHEN MY ALTIMETER INDICATED 1200 FT SHE TOLD ME SHE HAD ME AT 1800 FT AND THAT 2 1/2 MI BACK I HAD BEEN AT 2300 FT IN THE BRAVO SPACE. MY ENCODER WAS 600 FT IN ERROR. AT 1200 FT I WAS NEARLY LEVEL WITH THE 1014 FT RADIO TWRS OFF MY L WINGTIP. I AM GETTING MY ENCODER CALIBRATED/REPAIRED. THERE WAS NO INTRUSION INTO BRAVO AIRSPACE, HOWEVER, THE MODE C WAS RPTING 600 FT HIGHER THAN ACTUAL. I IMMEDIATELY VERIFIED A PROB BY CONNECTING A LORAN READOUT TO THE MODE C OUTPUT ONCE AT HOME ARPT. THE ERROR ON THE GND WAS ALSO 600 FT. THE UNIT WILL BE REPAIRED BEFORE FURTHER FLT.
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.