Narrative:

My altitude assignment was FL210. Descending from FL230 the company mechanic adjusted the altitude alert for FL210. I verified that FL210 was selected in the altitude alert. Descending through FL220 the altitude alert chime went off and I observed the light out of the corner of my eye. With 1000 ft to go to the assigned altitude, my focus became more concentrated on the radar (see sketch) our destination marked by tip of arrow, addison airport, tx. I was given a heading by ATC that would have placed me in the area in the closest proximity to the aircraft just left of the nose (shaded red returns). I could not accept this and requested a heading about 30 degrees right of what ATC wanted. This was approved, but I was advised that I could not hold this heading for long as I would be in dfw airspace. My descent rate was 500 FPM. I was also monitoring addison airport ATIS which was 700 ft broken, thunderstorm and rain. A crosswind of 12 KTS out of the west gusting to 15 KTS (since they were landing runway 33) occasional lightning could be seen in the distance north of the addison airport approximately 10 mi. In my mind I was evaluating whether to continue to addison or divert. I heard the altitude chime go off and saw the light on the altitude alert out of the corner of my eye. I thought I had 1000 ft to go, but I had just flown through my assigned altitude. At FL206 ATC advised 'maintain FL210 (pause) I'll tell you what make that FL200.' I complied and elected to continue to addison airport and landed. No evasive action was required. The incident occurred because of my shift in attention from altitude awareness to staying clear of thunderstorms, combined with listening to WX at addison, and evaluating that WX into a decision to whether to continue or divert, then which airport to divert to. I feel that this incident occurred because I normally fly single pilot, and on this particular day our company mechanic was trying to be helpful by adjusting my altitude alert for me. He didn't even notice that I flew through my altitude assigned, but that's not his responsibility. Maybe it was just enough of his helpfulness that took me out of the altitude awareness loop that contributed to this. Though, don't get the wrong idea. I accept full responsibility. In debriefing myself, I need to make adjustments should a high workload situation like that arise again, especially if someone else is assisting me.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION. PLT IS DISTRACTED BY WX AND OTHER DUTIES AND DSNDS BELOW HIS ASSIGNED ALT.

Narrative: MY ALT ASSIGNMENT WAS FL210. DSNDING FROM FL230 THE COMPANY MECH ADJUSTED THE ALT ALERT FOR FL210. I VERIFIED THAT FL210 WAS SELECTED IN THE ALT ALERT. DSNDING THROUGH FL220 THE ALT ALERT CHIME WENT OFF AND I OBSERVED THE LIGHT OUT OF THE CORNER OF MY EYE. WITH 1000 FT TO GO TO THE ASSIGNED ALT, MY FOCUS BECAME MORE CONCENTRATED ON THE RADAR (SEE SKETCH) OUR DEST MARKED BY TIP OF ARROW, ADDISON ARPT, TX. I WAS GIVEN A HDG BY ATC THAT WOULD HAVE PLACED ME IN THE AREA IN THE CLOSEST PROX TO THE ACFT JUST L OF THE NOSE (SHADED RED RETURNS). I COULD NOT ACCEPT THIS AND REQUESTED A HDG ABOUT 30 DEGS R OF WHAT ATC WANTED. THIS WAS APPROVED, BUT I WAS ADVISED THAT I COULD NOT HOLD THIS HDG FOR LONG AS I WOULD BE IN DFW AIRSPACE. MY DSCNT RATE WAS 500 FPM. I WAS ALSO MONITORING ADDISON ARPT ATIS WHICH WAS 700 FT BROKEN, TSTM AND RAIN. A XWIND OF 12 KTS OUT OF THE W GUSTING TO 15 KTS (SINCE THEY WERE LNDG RWY 33) OCCASIONAL LIGHTNING COULD BE SEEN IN THE DISTANCE N OF THE ADDISON ARPT APPROX 10 MI. IN MY MIND I WAS EVALUATING WHETHER TO CONTINUE TO ADDISON OR DIVERT. I HEARD THE ALT CHIME GO OFF AND SAW THE LIGHT ON THE ALT ALERT OUT OF THE CORNER OF MY EYE. I THOUGHT I HAD 1000 FT TO GO, BUT I HAD JUST FLOWN THROUGH MY ASSIGNED ALT. AT FL206 ATC ADVISED 'MAINTAIN FL210 (PAUSE) I'LL TELL YOU WHAT MAKE THAT FL200.' I COMPLIED AND ELECTED TO CONTINUE TO ADDISON ARPT AND LANDED. NO EVASIVE ACTION WAS REQUIRED. THE INCIDENT OCCURRED BECAUSE OF MY SHIFT IN ATTN FROM ALT AWARENESS TO STAYING CLR OF TSTMS, COMBINED WITH LISTENING TO WX AT ADDISON, AND EVALUATING THAT WX INTO A DECISION TO WHETHER TO CONTINUE OR DIVERT, THEN WHICH ARPT TO DIVERT TO. I FEEL THAT THIS INCIDENT OCCURRED BECAUSE I NORMALLY FLY SINGLE PLT, AND ON THIS PARTICULAR DAY OUR COMPANY MECH WAS TRYING TO BE HELPFUL BY ADJUSTING MY ALT ALERT FOR ME. HE DIDN'T EVEN NOTICE THAT I FLEW THROUGH MY ALT ASSIGNED, BUT THAT'S NOT HIS RESPONSIBILITY. MAYBE IT WAS JUST ENOUGH OF HIS HELPFULNESS THAT TOOK ME OUT OF THE ALT AWARENESS LOOP THAT CONTRIBUTED TO THIS. THOUGH, DON'T GET THE WRONG IDEA. I ACCEPT FULL RESPONSIBILITY. IN DEBRIEFING MYSELF, I NEED TO MAKE ADJUSTMENTS SHOULD A HIGH WORKLOAD SIT LIKE THAT ARISE AGAIN, ESPECIALLY IF SOMEONE ELSE IS ASSISTING ME.

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.