Narrative:

This will scare anyone who flies for a living. We were given a clearance to descend, our discretion, to FL250 and (we thought) cross lamma intersection at 250 KTS at 12000 ft. Both pilots heard the above clearance. In fact, the first officer, who was flying, set 12000 ft in the autoplt altitude window and then reset 25000 ft so as to stay high longer. We were shocked when the controller asked our altitude when we were about 24300 ft in descent. We were so convinced of the clearance that I requested a playback of the tape. Imagine our shock to find that the controller said to expect the lamma restriction and I read it back as it was issued! Unbelievable! I'm just tickled that the controller caught it after we had descended only 500 ft in a very busy, very narrow congested sector. He probably prevented us from killing somebody! It is terrifying to know that there is no procedure to compensate for the time when both pilots suffer a mental block at the same time. Supplemental information from acn 246367: ZJX cleared us for the blitha 6 arrival, then gave us 'pilot's discretion' to FL250, cross lamma 12000 ft and 250 KTS. That is how we read it back. At FL245 center said 'maintain FL240.'

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Original NASA ASRS Text

Title: CLRNC INTERP ACKNOWLEDGED YET FLC CREATED AN ALTDEV ALT EXCURSION IN A DSCNT PROC THAT ANTICIPATED AND USED THE 'EXPECT' XING ALT.

Narrative: THIS WILL SCARE ANYONE WHO FLIES FOR A LIVING. WE WERE GIVEN A CLRNC TO DSND, OUR DISCRETION, TO FL250 AND (WE THOUGHT) CROSS LAMMA INTXN AT 250 KTS AT 12000 FT. BOTH PLTS HEARD THE ABOVE CLRNC. IN FACT, THE FO, WHO WAS FLYING, SET 12000 FT IN THE AUTOPLT ALT WINDOW AND THEN RESET 25000 FT SO AS TO STAY HIGH LONGER. WE WERE SHOCKED WHEN THE CTLR ASKED OUR ALT WHEN WE WERE ABOUT 24300 FT IN DSCNT. WE WERE SO CONVINCED OF THE CLRNC THAT I REQUESTED A PLAYBACK OF THE TAPE. IMAGINE OUR SHOCK TO FIND THAT THE CTLR SAID TO EXPECT THE LAMMA RESTRICTION AND I READ IT BACK AS IT WAS ISSUED! UNBELIEVABLE! I'M JUST TICKLED THAT THE CTLR CAUGHT IT AFTER WE HAD DSNDED ONLY 500 FT IN A VERY BUSY, VERY NARROW CONGESTED SECTOR. HE PROBABLY PREVENTED US FROM KILLING SOMEBODY! IT IS TERRIFYING TO KNOW THAT THERE IS NO PROC TO COMPENSATE FOR THE TIME WHEN BOTH PLTS SUFFER A MENTAL BLOCK AT THE SAME TIME. SUPPLEMENTAL INFO FROM ACN 246367: ZJX CLRED US FOR THE BLITHA 6 ARR, THEN GAVE US 'PLT'S DISCRETION' TO FL250, CROSS LAMMA 12000 FT AND 250 KTS. THAT IS HOW WE READ IT BACK. AT FL245 CTR SAID 'MAINTAIN FL240.'

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.