Narrative:

Flight msy-tpa J-58, climbing through FL210 so noticed cabin was at 7500 ft and climbing at 500-700 FPM. I leveled aircraft at FL210 while we analyzed problem. We decided to descend until the cabin stabilized. This was at 17000 ft. We spent the rest of the flight trying to determine the exact cause, but we were unable. The flight continued normally to tpa. The next day we realized that we were technically in violation of our operation specifications which say that over water (over 50 mi from land) we need to be at FL250 or above. It occurred to us that with VOR navigation we would be low due to the large distance between vors, but our omega was working normally so we thought at the time all was ok. The WX was clear and smooth over the gulf but there were significant thunderstorms along the shoreline of the gulf, so we felt comfortable with our decision to stay on J-58. As I said, we didn't even think of the overwater requirement as a possibility until the next day. It may be a little obscure but it's something we should have considered. I suppose we just need to review operation specifications more often.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB. PRESSURIZATION PROB. CABIN DIDN'T STABILIZE UNTIL ACFT DSNDED TO 17000 FT. OVERWATER NAV ON VORS REQUIRE MINIMUM ALT OF FL250. FLC WAS NOT AWARE OF REG AT THE TIME.

Narrative: FLT MSY-TPA J-58, CLBING THROUGH FL210 SO NOTICED CABIN WAS AT 7500 FT AND CLBING AT 500-700 FPM. I LEVELED ACFT AT FL210 WHILE WE ANALYZED PROB. WE DECIDED TO DSND UNTIL THE CABIN STABILIZED. THIS WAS AT 17000 FT. WE SPENT THE REST OF THE FLT TRYING TO DETERMINE THE EXACT CAUSE, BUT WE WERE UNABLE. THE FLT CONTINUED NORMALLY TO TPA. THE NEXT DAY WE REALIZED THAT WE WERE TECHNICALLY IN VIOLATION OF OUR OP SPECS WHICH SAY THAT OVER WATER (OVER 50 MI FROM LAND) WE NEED TO BE AT FL250 OR ABOVE. IT OCCURRED TO US THAT WITH VOR NAV WE WOULD BE LOW DUE TO THE LARGE DISTANCE BTWN VORS, BUT OUR OMEGA WAS WORKING NORMALLY SO WE THOUGHT AT THE TIME ALL WAS OK. THE WX WAS CLR AND SMOOTH OVER THE GULF BUT THERE WERE SIGNIFICANT TSTMS ALONG THE SHORELINE OF THE GULF, SO WE FELT COMFORTABLE WITH OUR DECISION TO STAY ON J-58. AS I SAID, WE DIDN'T EVEN THINK OF THE OVERWATER REQUIREMENT AS A POSSIBILITY UNTIL THE NEXT DAY. IT MAY BE A LITTLE OBSCURE BUT IT'S SOMETHING WE SHOULD HAVE CONSIDERED. I SUPPOSE WE JUST NEED TO REVIEW OP SPECS MORE OFTEN.

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.