Narrative:

Air carrier X en route to bwi was about 60-70 mi southwest csn at FL270. I issued a clearance to cross csn at FL190. I was extremely busy at the time with another arrival fix (doccs) serving iad where I was mixing jets and propellers. I then had air carrier Y being handed off to me about 25 mi north gve descending from around FL273 to FL250. I accepted the handoff and immediately issued a new clearance to air carrier X to maintain FL260. I believe that I heard air carrier X readback but after listening to the tape, it sounded like 'garbled, ok, we'll stop it at 2, 6, 0'. I of course took it to be air carrier X's transmission. I was so busy at the time that I heard what I wanted to hear. I had no one else on the frequency at the time who was higher than FL270 who would've stopped their descent at FL260. Then when air carrier Y came on frequency, I turned him to 340 to pass behind air carrier X. This would've given me ample time to descend air carrier X to FL190 after they had passed. A couple of mins later I observed air carrier X passing FL253 with air carrier Y off his right about 2 1/2 mi. I advised air carrier X that he was to maintain FL260 only. He said last clearance he got was to cross csn at FL190. I issued traffic which he said he saw and I continued his descent to FL190. This I believe was the start of all that was to come. It sort of blew my mind. I knew I heard air carrier X read back to stop it at FL260 and who knows, maybe that garbled part at start of the transmission was his call sign. All this time that was spent on this event caused me to lose my timing on other events that were going on at the other arrival fix. Supplemental information from acn 178980: air carrier X was level at FL270 with washington center. Center cleared air carrier X to cross csn at FL190. Approximately 9-10 mi from top of descent the controller told us to start descent now to FL260. We assumed he needed us out of FL270 and needed us to get to FL260 as soon as possible. Because we were so close to descending to FL190 anyway we let the aircraft continue its descent to FL190. The controller was extremely busy and it was difficult to make radio transmission to him. I believe the confusion was from the improper terminology used by the controller as we passed through approximately FL250 he stated that he wanted us to stay at FL260. Normally when given a descent, eg, to FL190 and the controller wants you to stop your descent or doesn't want you to descend to the altitude previously cleared he will say 'stop your descent at FL260' or 'descend and maintain FL260'. When the controller stated 'start your descent now to FL260' that normally means he wants us to get to FL260 quickly, however, we are still cleared to FL190. Supplemental information from acn 179141: level at 27000 ft. Washington center cleared to cross casanova VOR (csn) at and maintain FL190. FMC was properly programmed for 19000 ft at csn and aircraft was 10 NM from top of descent, when controller instructed us to 'start your descent now to 26000 ft' (not sure of exact words). We executed capture mode, both pilots agreeing on this decision. Going through approximately 25000 ft controller asked us our altitude and/or what we were doing. We advised him we were descending to cross csn at 19000 ft. He then told us he wanted us to maintain 26000 ft and called traffic at 3 O'clock which we acquired. We were unable to establish what he wished us to do now, due to frequency congestion, so we continued so as to cross csn at 19000 ft.

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Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR X ENRTE TO BWI WAS ABOUT 60-70 MI SW CSN AT FL270. I ISSUED A CLRNC TO CROSS CSN AT FL190. I WAS EXTREMELY BUSY AT THE TIME WITH ANOTHER ARR FIX (DOCCS) SERVING IAD WHERE I WAS MIXING JETS AND PROPS. I THEN HAD ACR Y BEING HANDED OFF TO ME ABOUT 25 MI N GVE DSNDING FROM AROUND FL273 TO FL250. I ACCEPTED THE HDOF AND IMMEDIATELY ISSUED A NEW CLRNC TO ACR X TO MAINTAIN FL260. I BELIEVE THAT I HEARD ACR X READBACK BUT AFTER LISTENING TO THE TAPE, IT SOUNDED LIKE 'GARBLED, OK, WE'LL STOP IT AT 2, 6, 0'. I OF COURSE TOOK IT TO BE ACR X'S XMISSION. I WAS SO BUSY AT THE TIME THAT I HEARD WHAT I WANTED TO HEAR. I HAD NO ONE ELSE ON THE FREQ AT THE TIME WHO WAS HIGHER THAN FL270 WHO WOULD'VE STOPPED THEIR DSCNT AT FL260. THEN WHEN ACR Y CAME ON FREQ, I TURNED HIM TO 340 TO PASS BEHIND ACR X. THIS WOULD'VE GIVEN ME AMPLE TIME TO DSND ACR X TO FL190 AFTER THEY HAD PASSED. A COUPLE OF MINS LATER I OBSERVED ACR X PASSING FL253 WITH ACR Y OFF HIS R ABOUT 2 1/2 MI. I ADVISED ACR X THAT HE WAS TO MAINTAIN FL260 ONLY. HE SAID LAST CLRNC HE GOT WAS TO CROSS CSN AT FL190. I ISSUED TFC WHICH HE SAID HE SAW AND I CONTINUED HIS DSCNT TO FL190. THIS I BELIEVE WAS THE START OF ALL THAT WAS TO COME. IT SORT OF BLEW MY MIND. I KNEW I HEARD ACR X READ BACK TO STOP IT AT FL260 AND WHO KNOWS, MAYBE THAT GARBLED PART AT START OF THE XMISSION WAS HIS CALL SIGN. ALL THIS TIME THAT WAS SPENT ON THIS EVENT CAUSED ME TO LOSE MY TIMING ON OTHER EVENTS THAT WERE GOING ON AT THE OTHER ARR FIX. SUPPLEMENTAL INFO FROM ACN 178980: ACR X WAS LEVEL AT FL270 WITH WASHINGTON CENTER. CENTER CLRED ACR X TO CROSS CSN AT FL190. APPROX 9-10 MI FROM TOP OF DSCNT THE CTLR TOLD US TO START DSCNT NOW TO FL260. WE ASSUMED HE NEEDED US OUT OF FL270 AND NEEDED US TO GET TO FL260 AS SOON AS POSSIBLE. BECAUSE WE WERE SO CLOSE TO DSNDING TO FL190 ANYWAY WE LET THE ACFT CONTINUE ITS DSCNT TO FL190. THE CTLR WAS EXTREMELY BUSY AND IT WAS DIFFICULT TO MAKE RADIO XMISSION TO HIM. I BELIEVE THE CONFUSION WAS FROM THE IMPROPER TERMINOLOGY USED BY THE CTLR AS WE PASSED THROUGH APPROX FL250 HE STATED THAT HE WANTED US TO STAY AT FL260. NORMALLY WHEN GIVEN A DSCNT, EG, TO FL190 AND THE CTLR WANTS YOU TO STOP YOUR DSCNT OR DOESN'T WANT YOU TO DSND TO THE ALT PREVIOUSLY CLRED HE WILL SAY 'STOP YOUR DSCNT AT FL260' OR 'DSND AND MAINTAIN FL260'. WHEN THE CTLR STATED 'START YOUR DSCNT NOW TO FL260' THAT NORMALLY MEANS HE WANTS US TO GET TO FL260 QUICKLY, HOWEVER, WE ARE STILL CLRED TO FL190. SUPPLEMENTAL INFO FROM ACN 179141: LEVEL AT 27000 FT. WASHINGTON CENTER CLRED TO CROSS CASANOVA VOR (CSN) AT AND MAINTAIN FL190. FMC WAS PROPERLY PROGRAMMED FOR 19000 FT AT CSN AND ACFT WAS 10 NM FROM TOP OF DSCNT, WHEN CTLR INSTRUCTED US TO 'START YOUR DSCNT NOW TO 26000 FT' (NOT SURE OF EXACT WORDS). WE EXECUTED CAPTURE MODE, BOTH PLTS AGREEING ON THIS DECISION. GOING THROUGH APPROX 25000 FT CTLR ASKED US OUR ALT AND/OR WHAT WE WERE DOING. WE ADVISED HIM WE WERE DSNDING TO CROSS CSN AT 19000 FT. HE THEN TOLD US HE WANTED US TO MAINTAIN 26000 FT AND CALLED TFC AT 3 O'CLOCK WHICH WE ACQUIRED. WE WERE UNABLE TO ESTABLISH WHAT HE WISHED US TO DO NOW, DUE TO FREQ CONGESTION, SO WE CONTINUED SO AS TO CROSS CSN AT 19000 FT.

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.