Narrative:

Flight XXX was dispatched on a WX avoidance route that was longer than normal. The WX in question had moved east and allowed us to go on a more direct route but required us to burn more fuel to be under landing weight. We were at FL290; I requested FL230 from center at XA30Z. Center replied 'how about FL250 for now; I have to coordination for FL230.' I replied; 'roger; FL250 for XXXX;' and the first officer (PF) began the descent. About 1 min later; center asked what we were doing. The first officer replied to the call and center told us to level off at FL280; that we were not cleared to FL250. This occurred at FL283 and caused no loss of separation or other conflict. Nothing else was said to us. We were handed off to the next frequency and inquired about a lower altitude -- concerned about being at FL280 the wrong way; we received a vector and lower altitude and landed at XXX uneventfully and legally below mlw. Both the first officer and I acknowledged ATC's reply as a clearance and acted accordingly. The center never corrected us after reading back his clearance if; in fact; we did misunderstand him. Contributing factors were lots of WX and; therefore; many different aircraft on abnormal airways. Also; I had a reduced rest from the previous evening which definitely reduces sharpness the next day. In this case; I still believe that nonstandard phraseology had more to do with it. However; these are all contributing factors. Being rescheduled to fly without a meal break after a reduced rest overnight is a bad idea.

Google
 

Original NASA ASRS Text

Title: AN EMJ CREW COMMENCED A DSCNT FOLLOWING A REQUESTED CLRNC PHRASEOLOGY CONFUSION. ADDITIONALLY; CAPT CITES REDUCED REST THE PREVIOUS EVENING BEING A CONTRIBUTORY FACTOR.

Narrative: FLT XXX WAS DISPATCHED ON A WX AVOIDANCE RTE THAT WAS LONGER THAN NORMAL. THE WX IN QUESTION HAD MOVED E AND ALLOWED US TO GO ON A MORE DIRECT RTE BUT REQUIRED US TO BURN MORE FUEL TO BE UNDER LNDG WT. WE WERE AT FL290; I REQUESTED FL230 FROM CTR AT XA30Z. CTR REPLIED 'HOW ABOUT FL250 FOR NOW; I HAVE TO COORD FOR FL230.' I REPLIED; 'ROGER; FL250 FOR XXXX;' AND THE FO (PF) BEGAN THE DSCNT. ABOUT 1 MIN LATER; CTR ASKED WHAT WE WERE DOING. THE FO REPLIED TO THE CALL AND CTR TOLD US TO LEVEL OFF AT FL280; THAT WE WERE NOT CLRED TO FL250. THIS OCCURRED AT FL283 AND CAUSED NO LOSS OF SEPARATION OR OTHER CONFLICT. NOTHING ELSE WAS SAID TO US. WE WERE HANDED OFF TO THE NEXT FREQ AND INQUIRED ABOUT A LOWER ALT -- CONCERNED ABOUT BEING AT FL280 THE WRONG WAY; WE RECEIVED A VECTOR AND LOWER ALT AND LANDED AT XXX UNEVENTFULLY AND LEGALLY BELOW MLW. BOTH THE FO AND I ACKNOWLEDGED ATC'S REPLY AS A CLRNC AND ACTED ACCORDINGLY. THE CTR NEVER CORRECTED US AFTER READING BACK HIS CLRNC IF; IN FACT; WE DID MISUNDERSTAND HIM. CONTRIBUTING FACTORS WERE LOTS OF WX AND; THEREFORE; MANY DIFFERENT ACFT ON ABNORMAL AIRWAYS. ALSO; I HAD A REDUCED REST FROM THE PREVIOUS EVENING WHICH DEFINITELY REDUCES SHARPNESS THE NEXT DAY. IN THIS CASE; I STILL BELIEVE THAT NONSTANDARD PHRASEOLOGY HAD MORE TO DO WITH IT. HOWEVER; THESE ARE ALL CONTRIBUTING FACTORS. BEING RESCHEDULED TO FLY WITHOUT A MEAL BREAK AFTER A REDUCED REST OVERNIGHT IS A BAD IDEA.

Data retrieved from NASA's ASRS site as of January 2009 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.