Narrative:

Approximately 5 mins after leveling at FL410 during the cruise portion of the flight the incident occurred. At that time both the captain, who was in the left seat, and myself, noticed a line of very active thunderstorms both visually and on the radar. By observing the line visually, with the help of an almost full moon, we could tell that some of the cells exceeded our altitude. At that time, the captain told me to tell ZHU that we would need to deviate to the right (south) to avoid the line. ZHU approved the deviation and the captain, who was hand flying the aircraft, started a turn to the right. When the captain started his turn and while he was in the turn I was looking outside at the line of thunderstorms until I heard the altitude alert bell go off. At that time I looked inside the aircraft to find us 500 ft above our assigned altitude of FL410 and still climbing rapidly. At that time I called altitude to the captain and pointed at the altimeter. When the aircraft reached FL420 the captain turned off the transponder and started a descent to FL410. Upon reaching FL410 the captain reached over and turned the transponder back on at which time the flight proceeded normally. I feel that the sole cause of this incident is the poor flying skills on the part of the captain. I also feel that it was very poor practice of this captain to turn off the transponder, not to mention it is illegal. Turning off the transponder did nothing more than increase the risk of a conflict with another aircraft. Supplemental information from acn 238715: flying to cozumel, mexico, from san antonio, tx, to pick up a patient, with autoplt inoperative at cruise 41000 ft north A-766 over the gulf near barow intersection. Line of thunderstorm front extending to 45000 ft from our position to new orleans. Radar was painting WX and aircraft was in turbulence. Aircraft altitude was bouncing on the altimeter plus/minus 200 ft. I was PF, noticed cloud to cloud lightning to our front, made a 90 degree turn to right to avoid WX, and I feel definite lightning strike on aircraft. When I started the turn to my right, evidently I was already 400 ft high. I rolled out at 42000 ft, noticed it and immediately descended and maintained my assigned altitude of 41000 ft. ZHU made no mention of it to us. We avoided WX and remainder of the flight was uneventful.

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Original NASA ASRS Text

Title: LTT CLBS 1000 FT ABOVE ASSIGNED ALT AND TURNS OFF XPONDER TO HIDE THE FACT.

Narrative: APPROX 5 MINS AFTER LEVELING AT FL410 DURING THE CRUISE PORTION OF THE FLT THE INCIDENT OCCURRED. AT THAT TIME BOTH THE CAPT, WHO WAS IN THE L SEAT, AND MYSELF, NOTICED A LINE OF VERY ACTIVE TSTMS BOTH VISUALLY AND ON THE RADAR. BY OBSERVING THE LINE VISUALLY, WITH THE HELP OF AN ALMOST FULL MOON, WE COULD TELL THAT SOME OF THE CELLS EXCEEDED OUR ALT. AT THAT TIME, THE CAPT TOLD ME TO TELL ZHU THAT WE WOULD NEED TO DEVIATE TO THE R (S) TO AVOID THE LINE. ZHU APPROVED THE DEV AND THE CAPT, WHO WAS HAND FLYING THE ACFT, STARTED A TURN TO THE R. WHEN THE CAPT STARTED HIS TURN AND WHILE HE WAS IN THE TURN I WAS LOOKING OUTSIDE AT THE LINE OF TSTMS UNTIL I HEARD THE ALT ALERT BELL GO OFF. AT THAT TIME I LOOKED INSIDE THE ACFT TO FIND US 500 FT ABOVE OUR ASSIGNED ALT OF FL410 AND STILL CLBING RAPIDLY. AT THAT TIME I CALLED ALT TO THE CAPT AND POINTED AT THE ALTIMETER. WHEN THE ACFT REACHED FL420 THE CAPT TURNED OFF THE XPONDER AND STARTED A DSCNT TO FL410. UPON REACHING FL410 THE CAPT REACHED OVER AND TURNED THE XPONDER BACK ON AT WHICH TIME THE FLT PROCEEDED NORMALLY. I FEEL THAT THE SOLE CAUSE OF THIS INCIDENT IS THE POOR FLYING SKILLS ON THE PART OF THE CAPT. I ALSO FEEL THAT IT WAS VERY POOR PRACTICE OF THIS CAPT TO TURN OFF THE XPONDER, NOT TO MENTION IT IS ILLEGAL. TURNING OFF THE XPONDER DID NOTHING MORE THAN INCREASE THE RISK OF A CONFLICT WITH ANOTHER ACFT. SUPPLEMENTAL INFO FROM ACN 238715: FLYING TO COZUMEL, MEXICO, FROM SAN ANTONIO, TX, TO PICK UP A PATIENT, WITH AUTOPLT INOP AT CRUISE 41000 FT N A-766 OVER THE GULF NEAR BAROW INTXN. LINE OF TSTM FRONT EXTENDING TO 45000 FT FROM OUR POS TO NEW ORLEANS. RADAR WAS PAINTING WX AND ACFT WAS IN TURB. ACFT ALT WAS BOUNCING ON THE ALTIMETER PLUS/MINUS 200 FT. I WAS PF, NOTICED CLOUD TO CLOUD LIGHTNING TO OUR FRONT, MADE A 90 DEG TURN TO R TO AVOID WX, AND I FEEL DEFINITE LIGHTNING STRIKE ON ACFT. WHEN I STARTED THE TURN TO MY R, EVIDENTLY I WAS ALREADY 400 FT HIGH. I ROLLED OUT AT 42000 FT, NOTICED IT AND IMMEDIATELY DSNDED AND MAINTAINED MY ASSIGNED ALT OF 41000 FT. ZHU MADE NO MENTION OF IT TO US. WE AVOIDED WX AND REMAINDER OF THE FLT WAS UNEVENTFUL.

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.