Narrative:

ZBW told us to cross bronc intersection at 10000'. We questioned center as STAR reads 'expect to cross at 11000 at 250K.' when level at 10000', ZBW asked us to say our altitude. We responded 10000'. They responded we were told to maintain 11000'. In turn, we said we read back 10000' twice, as it differed with STAR gardner 2 arrival. They said to maintain 10000' and there would be no problem. Callback conversation with reporter revealed the following: when descent clearance was issued the PIC (reporter) was in the lav, and when he returned to cockpit ATC was questioning altitude and first officer was telling controller that he understood clearance to 10000' and had read it back twice. Reporter not sure if first officer used digit form (1-0-thousand), or group form (10-thousand) in readback. Says that ZBW controller was trnee and instrument controller came on air to say that there was no conflict and no problem. Later, after frequency change to approach control, the PIC went back to ZBW controller to reaffirm that there would be no follow-up on the incident.

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Original NASA ASRS Text

Title: MISUNDERSTANDING OF ALT ASSIGNMENT INVOLVING 1-1-THOUSAND AND 1-0-THOUSAND. ACR DESCENT TO 10000' IN ERROR.

Narrative: ZBW TOLD US TO CROSS BRONC INTXN AT 10000'. WE QUESTIONED CENTER AS STAR READS 'EXPECT TO CROSS AT 11000 AT 250K.' WHEN LEVEL AT 10000', ZBW ASKED US TO SAY OUR ALT. WE RESPONDED 10000'. THEY RESPONDED WE WERE TOLD TO MAINTAIN 11000'. IN TURN, WE SAID WE READ BACK 10000' TWICE, AS IT DIFFERED WITH STAR GARDNER 2 ARR. THEY SAID TO MAINTAIN 10000' AND THERE WOULD BE NO PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: WHEN DSCNT CLRNC WAS ISSUED THE PIC (RPTR) WAS IN THE LAV, AND WHEN HE RETURNED TO COCKPIT ATC WAS QUESTIONING ALT AND F/O WAS TELLING CTLR THAT HE UNDERSTOOD CLRNC TO 10000' AND HAD READ IT BACK TWICE. RPTR NOT SURE IF F/O USED DIGIT FORM (1-0-THOUSAND), OR GROUP FORM (10-THOUSAND) IN READBACK. SAYS THAT ZBW CTLR WAS TRNEE AND INSTR CTLR CAME ON AIR TO SAY THAT THERE WAS NO CONFLICT AND NO PROB. LATER, AFTER FREQ CHANGE TO APCH CTL, THE PIC WENT BACK TO ZBW CTLR TO REAFFIRM THAT THERE WOULD BE NO FOLLOW-UP ON THE INCIDENT.

Data retrieved from NASA's ASRS site as of August 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.