Narrative:

We were climbing out of miami on the 8TH leg of the night (although it was now daytime) and having flown 7 and a half hours. Our initial clearance was runway heading left to 5000 ft, then the controller gave us a clearance to turn to 360 degrees and 7000 ft. With the warm sunshine and fatigue setting in, my mind must have started to wander. The next thing I knew, the (PF) captain was descending through 9000 ft on the way back to 7000 ft. Our altitude alerter had been intermittent all night and had obviously not worked in this particular instance. The PF swore he had heard a clearance to climb to 16000 ft, but descended back down to 7000 ft when he glanced at the altitude alerter and saw 7000 ft set in it. I could honestly not remember receiving a clearance to 16000 ft and had not changed the altitude alerter, but I still did not see him fly through our 'assigned' altitude (if that was our assigned altitude). When I asked the controller for verification of our assigned altitude -- he seemed as confused as us. He thought he had given us 16000 ft but honestly could not remember. It seems obvious that no conflict had taken place. The captain (who does not fly this route as often as I do) felt that it was possible he had heard a clearance for someone else. He also said that if 7000 ft was our assigned altitude we should not have climbed, and if 16000 ft was our assigned altitude we should not have descended. I still could not remember receiving or reading back a clearance to 16000 ft and was kicking myself for not catching the pilot flying through 7000 ft. Needless to say I felt bad all the way home. Factors that brought about this situation, I feel, are an intermittent altitude alerter. We become conditioned to hearing it ring and warning us (even saving us sometimes). The altitude alerter is deferrable in some cases. Fatigue. We fly a long night (8 legs, 8 plus hours of flying) if we fly this 4 nights a week we will reach the maximum for the yr about 1 1/2 months before the yr ends. For our type of flying (part 135, on demand, even though we have a 'schedule'), that is 1400 hours. I have quite some stamina. I have never complained about this schedule and never felt it could affect my work as a whole, but I can see now how it can catch up with you and affect your performance and I understand why most other pilots in airline and scheduled operations are restr to 1000 hours per yr. Complacency, even a very experienced crew flying in good conditions only needs for one of them to let their guard down temporarily for an incident or potential hazard to occur. I hope I have learned my lesson and am very thankful that nothing worse than embarrassment was the result. Note to researcher: I would appreciate it if this report ends up being published, sufficient details are changed (altitudes, places, number of legs, etc) to assure that no one can correlate it with me as no one else knows about this.

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Original NASA ASRS Text

Title: ALTDEV.

Narrative: WE WERE CLBING OUT OF MIAMI ON THE 8TH LEG OF THE NIGHT (ALTHOUGH IT WAS NOW DAYTIME) AND HAVING FLOWN 7 AND A HALF HRS. OUR INITIAL CLRNC WAS RWY HDG L TO 5000 FT, THEN THE CTLR GAVE US A CLRNC TO TURN TO 360 DEGS AND 7000 FT. WITH THE WARM SUNSHINE AND FATIGUE SETTING IN, MY MIND MUST HAVE STARTED TO WANDER. THE NEXT THING I KNEW, THE (PF) CAPT WAS DSNDING THROUGH 9000 FT ON THE WAY BACK TO 7000 FT. OUR ALT ALERTER HAD BEEN INTERMITTENT ALL NIGHT AND HAD OBVIOUSLY NOT WORKED IN THIS PARTICULAR INSTANCE. THE PF SWORE HE HAD HEARD A CLRNC TO CLB TO 16000 FT, BUT DSNDED BACK DOWN TO 7000 FT WHEN HE GLANCED AT THE ALT ALERTER AND SAW 7000 FT SET IN IT. I COULD HONESTLY NOT REMEMBER RECEIVING A CLRNC TO 16000 FT AND HAD NOT CHANGED THE ALT ALERTER, BUT I STILL DID NOT SEE HIM FLY THROUGH OUR 'ASSIGNED' ALT (IF THAT WAS OUR ASSIGNED ALT). WHEN I ASKED THE CTLR FOR VERIFICATION OF OUR ASSIGNED ALT -- HE SEEMED AS CONFUSED AS US. HE THOUGHT HE HAD GIVEN US 16000 FT BUT HONESTLY COULD NOT REMEMBER. IT SEEMS OBVIOUS THAT NO CONFLICT HAD TAKEN PLACE. THE CAPT (WHO DOES NOT FLY THIS RTE AS OFTEN AS I DO) FELT THAT IT WAS POSSIBLE HE HAD HEARD A CLRNC FOR SOMEONE ELSE. HE ALSO SAID THAT IF 7000 FT WAS OUR ASSIGNED ALT WE SHOULD NOT HAVE CLBED, AND IF 16000 FT WAS OUR ASSIGNED ALT WE SHOULD NOT HAVE DSNDED. I STILL COULD NOT REMEMBER RECEIVING OR READING BACK A CLRNC TO 16000 FT AND WAS KICKING MYSELF FOR NOT CATCHING THE PLT FLYING THROUGH 7000 FT. NEEDLESS TO SAY I FELT BAD ALL THE WAY HOME. FACTORS THAT BROUGHT ABOUT THIS SIT, I FEEL, ARE AN INTERMITTENT ALT ALERTER. WE BECOME CONDITIONED TO HEARING IT RING AND WARNING US (EVEN SAVING US SOMETIMES). THE ALT ALERTER IS DEFERRABLE IN SOME CASES. FATIGUE. WE FLY A LONG NIGHT (8 LEGS, 8 PLUS HRS OF FLYING) IF WE FLY THIS 4 NIGHTS A WK WE WILL REACH THE MAXIMUM FOR THE YR ABOUT 1 1/2 MONTHS BEFORE THE YR ENDS. FOR OUR TYPE OF FLYING (PART 135, ON DEMAND, EVEN THOUGH WE HAVE A 'SCHEDULE'), THAT IS 1400 HRS. I HAVE QUITE SOME STAMINA. I HAVE NEVER COMPLAINED ABOUT THIS SCHEDULE AND NEVER FELT IT COULD AFFECT MY WORK AS A WHOLE, BUT I CAN SEE NOW HOW IT CAN CATCH UP WITH YOU AND AFFECT YOUR PERFORMANCE AND I UNDERSTAND WHY MOST OTHER PLTS IN AIRLINE AND SCHEDULED OPS ARE RESTR TO 1000 HRS PER YR. COMPLACENCY, EVEN A VERY EXPERIENCED CREW FLYING IN GOOD CONDITIONS ONLY NEEDS FOR ONE OF THEM TO LET THEIR GUARD DOWN TEMPORARILY FOR AN INCIDENT OR POTENTIAL HAZARD TO OCCUR. I HOPE I HAVE LEARNED MY LESSON AND AM VERY THANKFUL THAT NOTHING WORSE THAN EMBARRASSMENT WAS THE RESULT. NOTE TO RESEARCHER: I WOULD APPRECIATE IT IF THIS RPT ENDS UP BEING PUBLISHED, SUFFICIENT DETAILS ARE CHANGED (ALTS, PLACES, NUMBER OF LEGS, ETC) TO ASSURE THAT NO ONE CAN CORRELATE IT WITH ME AS NO ONE ELSE KNOWS ABOUT THIS.

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.