Narrative:

I attempted to follow the blue VFR route around the west side of las vegas. I was informed by the vgt tower that I had violated the class B airspace of las international. I was told to contact approach on an assigned frequency, which I did. My plan was to follow the route over the ceiling of 4500 ft for vgt and under the floor of 5000 ft for the class B airspace above. I got the altimeter setting from vgt ATIS of 30.03 and flew at 4700 ft to go through the window. I tuned to vgt tower frequency. My transponder was set to 1200 and the light was flashing as I was 'painted.' the transponder had been on this setting the whole trip with the light flashing. As I was directly over vgt, the tower asked the cessna directly over the field to give its call sign. I did. The reply was that I should contact approach on the assigned frequency, which I did. A controller asked me to squawk a code and identify. Controller said she could not see me. I turned the knob back to 'altitude.' controller then saw me and asked my altitude. I had begun my descent to get below the 4000 ft floor. Controller asked my altitude again, I replied 4000 ft and she said she showed me as 4100 ft so I went lower. Controller asked me my destination and I replied the los angeles area. Controller gave me a telephone number to copy down, and said for me to call in. Barstow-daggett was the next place that was attended, so I landed there and telephoned. I spoke with a gentleman. He seemed familiar with what had happened and spoke with the female controller who had handled me. He took notes on what I said. His advice, that I now will always follow, is that approach would always prefer that when I reach the mode C veil that even though I am making a VFR transit, I should ask for a squawk code and they would vector me through the area. He also said, when I approached los angeles I should ask for a transponder check. I did that and lax approach reported that they could see my ok. They said they would check the altitude sensing of the transponder.

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Original NASA ASRS Text

Title: C172 VIOLATES LAS MODE C XPONDER VEIL.

Narrative: I ATTEMPTED TO FOLLOW THE BLUE VFR RTE AROUND THE W SIDE OF LAS VEGAS. I WAS INFORMED BY THE VGT TWR THAT I HAD VIOLATED THE CLASS B AIRSPACE OF LAS INTL. I WAS TOLD TO CONTACT APCH ON AN ASSIGNED FREQ, WHICH I DID. MY PLAN WAS TO FOLLOW THE RTE OVER THE CEILING OF 4500 FT FOR VGT AND UNDER THE FLOOR OF 5000 FT FOR THE CLASS B AIRSPACE ABOVE. I GOT THE ALTIMETER SETTING FROM VGT ATIS OF 30.03 AND FLEW AT 4700 FT TO GO THROUGH THE WINDOW. I TUNED TO VGT TWR FREQ. MY XPONDER WAS SET TO 1200 AND THE LIGHT WAS FLASHING AS I WAS 'PAINTED.' THE XPONDER HAD BEEN ON THIS SETTING THE WHOLE TRIP WITH THE LIGHT FLASHING. AS I WAS DIRECTLY OVER VGT, THE TWR ASKED THE CESSNA DIRECTLY OVER THE FIELD TO GIVE ITS CALL SIGN. I DID. THE REPLY WAS THAT I SHOULD CONTACT APCH ON THE ASSIGNED FREQ, WHICH I DID. A CTLR ASKED ME TO SQUAWK A CODE AND IDENT. CTLR SAID SHE COULD NOT SEE ME. I TURNED THE KNOB BACK TO 'ALT.' CTLR THEN SAW ME AND ASKED MY ALT. I HAD BEGUN MY DSCNT TO GET BELOW THE 4000 FT FLOOR. CTLR ASKED MY ALT AGAIN, I REPLIED 4000 FT AND SHE SAID SHE SHOWED ME AS 4100 FT SO I WENT LOWER. CTLR ASKED ME MY DEST AND I REPLIED THE LOS ANGELES AREA. CTLR GAVE ME A TELEPHONE NUMBER TO COPY DOWN, AND SAID FOR ME TO CALL IN. BARSTOW-DAGGETT WAS THE NEXT PLACE THAT WAS ATTENDED, SO I LANDED THERE AND TELEPHONED. I SPOKE WITH A GENTLEMAN. HE SEEMED FAMILIAR WITH WHAT HAD HAPPENED AND SPOKE WITH THE FEMALE CTLR WHO HAD HANDLED ME. HE TOOK NOTES ON WHAT I SAID. HIS ADVICE, THAT I NOW WILL ALWAYS FOLLOW, IS THAT APCH WOULD ALWAYS PREFER THAT WHEN I REACH THE MODE C VEIL THAT EVEN THOUGH I AM MAKING A VFR TRANSIT, I SHOULD ASK FOR A SQUAWK CODE AND THEY WOULD VECTOR ME THROUGH THE AREA. HE ALSO SAID, WHEN I APCHED LOS ANGELES I SHOULD ASK FOR A XPONDER CHK. I DID THAT AND LAX APCH RPTED THAT THEY COULD SEE MY OK. THEY SAID THEY WOULD CHK THE ALT SENSING OF THE XPONDER.

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.