Narrative:

Upon arrival (on final) at fresno air terminal, the tower informed me that my mode C indicated '1 foot'. (I was about 1000 AGL.) several hours later, upon departure at several hundred feet, the tower instructed me to 'please turn off your mode C'. I did not immediately respond because I was intently flying the plane. A significant amount of traffic was present in the area and most importantly I could not immediately determine the meaning of the instructions. My failure to respond agitated the tower and his second call was terse and commanding. If he was using the words altitude encoder I could not register exactly what action I was supposed to be taking. I requested a repeat. I believe he requested my indicated altitude and altimeter setting. I remember stating the four possible settings on my transponder on, off, altitude, and standby -- could he tell me which setting he was requesting. I asked if I should turn the transponder off? 'No, no, I need that on' was the reply. At about this point the tower said 'just leave it along, lady', clearly annoyed. The remainder of my flight was uneventful. I failed to recognize, upon arrival at fat the significance of the '1 foot' information from the tower. Had I spent even a few moments thinking thru the malfunctioning mode C I could have taken corrective action upon departure and avoided the departure problem completely. Another contributing factor was the fact that this was my 1ST arsa experience and my anxiety and experience limited my ability to take in the information the tower was trying to provide me. My passenger had only had one other light/small plane experience and I was peripherally aware that my exchange with the tower, to her, probably meant we were on the verge of falling out of the sky. The malfunctioning mode C was reported to the FBO upon my return.

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Original NASA ASRS Text

Title: SMA PLT HAD MALFUNCTIONING MODE C. DID NOT UNDERSTAND CTLR REQUEST TO TURN OFF ALT REPORTING FUNCTION.

Narrative: UPON ARR (ON FINAL) AT FRESNO AIR TERMINAL, THE TWR INFORMED ME THAT MY MODE C INDICATED '1 FOOT'. (I WAS ABOUT 1000 AGL.) SEVERAL HRS LATER, UPON DEP AT SEVERAL HUNDRED FEET, THE TWR INSTRUCTED ME TO 'PLEASE TURN OFF YOUR MODE C'. I DID NOT IMMEDIATELY RESPOND BECAUSE I WAS INTENTLY FLYING THE PLANE. A SIGNIFICANT AMOUNT OF TFC WAS PRESENT IN THE AREA AND MOST IMPORTANTLY I COULD NOT IMMEDIATELY DETERMINE THE MEANING OF THE INSTRUCTIONS. MY FAILURE TO RESPOND AGITATED THE TWR AND HIS SECOND CALL WAS TERSE AND COMMANDING. IF HE WAS USING THE WORDS ALT ENCODER I COULD NOT REGISTER EXACTLY WHAT ACTION I WAS SUPPOSED TO BE TAKING. I REQUESTED A REPEAT. I BELIEVE HE REQUESTED MY INDICATED ALT AND ALTIMETER SETTING. I REMEMBER STATING THE FOUR POSSIBLE SETTINGS ON MY XPONDER ON, OFF, ALT, AND STANDBY -- COULD HE TELL ME WHICH SETTING HE WAS REQUESTING. I ASKED IF I SHOULD TURN THE XPONDER OFF? 'NO, NO, I NEED THAT ON' WAS THE REPLY. AT ABOUT THIS POINT THE TWR SAID 'JUST LEAVE IT ALONG, LADY', CLEARLY ANNOYED. THE REMAINDER OF MY FLT WAS UNEVENTFUL. I FAILED TO RECOGNIZE, UPON ARR AT FAT THE SIGNIFICANCE OF THE '1 FOOT' INFORMATION FROM THE TWR. HAD I SPENT EVEN A FEW MOMENTS THINKING THRU THE MALFUNCTIONING MODE C I COULD HAVE TAKEN CORRECTIVE ACTION UPON DEP AND AVOIDED THE DEP PROBLEM COMPLETELY. ANOTHER CONTRIBUTING FACTOR WAS THE FACT THAT THIS WAS MY 1ST ARSA EXPERIENCE AND MY ANXIETY AND EXPERIENCE LIMITED MY ABILITY TO TAKE IN THE INFO THE TWR WAS TRYING TO PROVIDE ME. MY PAX HAD ONLY HAD ONE OTHER LIGHT/SMALL PLANE EXPERIENCE AND I WAS PERIPHERALLY AWARE THAT MY EXCHANGE WITH THE TWR, TO HER, PROBABLY MEANT WE WERE ON THE VERGE OF FALLING OUT OF THE SKY. THE MALFUNCTIONING MODE C WAS REPORTED TO THE FBO UPON MY RETURN.

Data retrieved from NASA's ASRS site as of August 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.