Narrative:

I was on an IFR flight at 6000', approximately 2/3 the way between farmington, mo and amarillo, tx, when ATC handed me off to an approach control frequency. I reported level 6000' and I got a report back from approach with the altimeter readings which I acknowledged. Then I began to calculate whether or not I could extend my flight to abq, and while I was intently analyzing my fuel and distance to extend the flight, approach called me to confirm level 6000'. Upon checking my altimeter I replied, 'negative, 5400 and climbing,' and, 'I must have knocked off my autoplt,' which was on navigation and altitude hold. Then I climbed to 6000' and reported it to approach which acknowledged the report. Nothing more was said except routine reports and change of frequency. My inadvertent disconnect usually occurs when I have my left hand on the top of the yolk and finger the remote microphone button with the forefinger causing a corresponding contraction of the thumb which may touch, very gently, the disconnect switch. Callback conversation with reporter revealed the following: reporter said that there is no visibility autoplt disconnect warning, and the aural warning buzzer is inaudible. Analyst suggested that the reporter contact the FAA to see about altering the autoplt disconnect switch location, and adding a warning light.

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Original NASA ASRS Text

Title: SMA PLT INADVERTENTLY DISCONNECTS AUTOPLT WHILE AT CRUISE AND EXPERIENCES AN ALT EXCURSION.

Narrative: I WAS ON AN IFR FLT AT 6000', APPROX 2/3 THE WAY BTWN FARMINGTON, MO AND AMARILLO, TX, WHEN ATC HANDED ME OFF TO AN APCH CTL FREQ. I RPTED LEVEL 6000' AND I GOT A RPT BACK FROM APCH WITH THE ALTIMETER READINGS WHICH I ACKNOWLEDGED. THEN I BEGAN TO CALCULATE WHETHER OR NOT I COULD EXTEND MY FLT TO ABQ, AND WHILE I WAS INTENTLY ANALYZING MY FUEL AND DISTANCE TO EXTEND THE FLT, APCH CALLED ME TO CONFIRM LEVEL 6000'. UPON CHKING MY ALTIMETER I REPLIED, 'NEGATIVE, 5400 AND CLBING,' AND, 'I MUST HAVE KNOCKED OFF MY AUTOPLT,' WHICH WAS ON NAV AND ALT HOLD. THEN I CLBED TO 6000' AND RPTED IT TO APCH WHICH ACKNOWLEDGED THE RPT. NOTHING MORE WAS SAID EXCEPT ROUTINE RPTS AND CHANGE OF FREQ. MY INADVERTENT DISCONNECT USUALLY OCCURS WHEN I HAVE MY LEFT HAND ON THE TOP OF THE YOLK AND FINGER THE REMOTE MIC BUTTON WITH THE FOREFINGER CAUSING A CORRESPONDING CONTRACTION OF THE THUMB WHICH MAY TOUCH, VERY GENTLY, THE DISCONNECT SWITCH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR SAID THAT THERE IS NO VIS AUTOPLT DISCONNECT WARNING, AND THE AURAL WARNING BUZZER IS INAUDIBLE. ANALYST SUGGESTED THAT THE RPTR CONTACT THE FAA TO SEE ABOUT ALTERING THE AUTOPLT DISCONNECT SWITCH LOCATION, AND ADDING A WARNING LIGHT.

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.