Narrative:

During cruise flight from buf to bos at FL290, I responded to and read back a clearance to FL250. The first officer and I pointed to the altitude setting and verbally confirmed the altitude change. While descending, the ZBW controller asked us to say assigned altitude, and we responded 'passing through FL275 for FL250.' he said the clearance we had acknowledged on readback was for another aircraft, but he said that he understood the confusion involved and 'no harm was done.' soon after, further clearance was issued to FL210. No separation errors resulted and no traffic was observed on TCASII within 20 NM. I think the new ATC procedures that allow a controller to ignore an incorrect readback was the main factor in this misunderstanding. Also there was a lot of backgnd noise on ZBW frequency 135.32.

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Original NASA ASRS Text

Title: DC9 CREW HAD ALTDEV.

Narrative: DURING CRUISE FLT FROM BUF TO BOS AT FL290, I RESPONDED TO AND READ BACK A CLRNC TO FL250. THE FO AND I POINTED TO THE ALT SETTING AND VERBALLY CONFIRMED THE ALT CHANGE. WHILE DSNDING, THE ZBW CTLR ASKED US TO SAY ASSIGNED ALT, AND WE RESPONDED 'PASSING THROUGH FL275 FOR FL250.' HE SAID THE CLRNC WE HAD ACKNOWLEDGED ON READBACK WAS FOR ANOTHER ACFT, BUT HE SAID THAT HE UNDERSTOOD THE CONFUSION INVOLVED AND 'NO HARM WAS DONE.' SOON AFTER, FURTHER CLRNC WAS ISSUED TO FL210. NO SEPARATION ERRORS RESULTED AND NO TFC WAS OBSERVED ON TCASII WITHIN 20 NM. I THINK THE NEW ATC PROCS THAT ALLOW A CTLR TO IGNORE AN INCORRECT READBACK WAS THE MAIN FACTOR IN THIS MISUNDERSTANDING. ALSO THERE WAS A LOT OF BACKGND NOISE ON ZBW FREQ 135.32.

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.