Narrative:

Air carrier X cruising at FL350 entre to ft wayne. ZID gave us a clearance of 'descend now to FL330, the pilot discretion to FL280.' I set 280 in the altitude window of the autoplt and 330 in the FMS. Prior to level off at FL330, ZID said 'continue descent to FL310.' I acknowledged and put FL310 into the FMS. We changed ZID frequency to 128.22 and I reported in with 'descending to 310, pilot discretion to FL280.' then the controller said 'continue descent to FL290.' I acknowledged FL290 as the assigned, but FL280 was still at our discretion. As we continued descent to 280, we noticed traffic Y at our 10 O'clock and about 6-7 mi. We were at about FL283 and started a climb just as ZID asked about our altitude. ZID told us to go back to FL290 and the conflicting traffic Y to descend to FL240. We had the traffic in sight the entire time and no TCASII warnings came on. There was an obvious miscom either between controllers or me and the controller. I acknowledged to both controllers that I had discretion to FL280. The problem was 4 different atl assignments within a few mins of each other and a frequency change. The controller needed to use a different word or phrase to cancel my FL280 clearance. Supplemental information from acn 261644: we were descending through about 28600 ft when we saw an aircraft on TCASII at FL280, 10 O'clock position, and approximately 6-7 mi out. At about 28400 ft we stopped our descent and started a slow climb back to FL290. As soon as our climb was initiated atl asked our altitude. We told ATC. They directed the other aircraft to expedite to FL240 and us to climb back to FL290. Although we still thought we had pilot's discretion to FL280, it would have helped if there was a reminder to cancel the pilot discretion to FL280, because of all the 2000 ft stepdowns. Supplemental information from acn 261525: air carrier X (MD88) was assigned FL290 and conflicted with cpr Y (HS25) who was converging at FL280. Supplemental information from acn 261524: cpr Y was at FL280. Air carrier X was cleared to FL290. Air carrier X began descending out of FL290. When air carrier X was approximately FL285, controller asked air carrier X his assigned altitude. Air carrier X said he was cleared pilot's discretion to FL280. Tape readback verified air carrier X read back FL290 on initial clearance, thus a pilot deviation.

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Original NASA ASRS Text

Title: ACR X UNAUTH DSCNT THROUGH ASSIGNED ALT HAD LTSS FROM CPR Y. PLTDEV.

Narrative: ACR X CRUISING AT FL350 ENTRE TO FT WAYNE. ZID GAVE US A CLRNC OF 'DSND NOW TO FL330, THE PLT DISCRETION TO FL280.' I SET 280 IN THE ALT WINDOW OF THE AUTOPLT AND 330 IN THE FMS. PRIOR TO LEVEL OFF AT FL330, ZID SAID 'CONTINUE DSCNT TO FL310.' I ACKNOWLEDGED AND PUT FL310 INTO THE FMS. WE CHANGED ZID FREQ TO 128.22 AND I RPTED IN WITH 'DSNDING TO 310, PLT DISCRETION TO FL280.' THEN THE CTLR SAID 'CONTINUE DSCNT TO FL290.' I ACKNOWLEDGED FL290 AS THE ASSIGNED, BUT FL280 WAS STILL AT OUR DISCRETION. AS WE CONTINUED DSCNT TO 280, WE NOTICED TFC Y AT OUR 10 O'CLOCK AND ABOUT 6-7 MI. WE WERE AT ABOUT FL283 AND STARTED A CLB JUST AS ZID ASKED ABOUT OUR ALT. ZID TOLD US TO GO BACK TO FL290 AND THE CONFLICTING TFC Y TO DSND TO FL240. WE HAD THE TFC IN SIGHT THE ENTIRE TIME AND NO TCASII WARNINGS CAME ON. THERE WAS AN OBVIOUS MISCOM EITHER BTWN CTLRS OR ME AND THE CTLR. I ACKNOWLEDGED TO BOTH CTLRS THAT I HAD DISCRETION TO FL280. THE PROB WAS 4 DIFFERENT ATL ASSIGNMENTS WITHIN A FEW MINS OF EACH OTHER AND A FREQ CHANGE. THE CTLR NEEDED TO USE A DIFFERENT WORD OR PHRASE TO CANCEL MY FL280 CLRNC. SUPPLEMENTAL INFO FROM ACN 261644: WE WERE DSNDING THROUGH ABOUT 28600 FT WHEN WE SAW AN ACFT ON TCASII AT FL280, 10 O'CLOCK POS, AND APPROX 6-7 MI OUT. AT ABOUT 28400 FT WE STOPPED OUR DSCNT AND STARTED A SLOW CLB BACK TO FL290. AS SOON AS OUR CLB WAS INITIATED ATL ASKED OUR ALT. WE TOLD ATC. THEY DIRECTED THE OTHER ACFT TO EXPEDITE TO FL240 AND US TO CLB BACK TO FL290. ALTHOUGH WE STILL THOUGHT WE HAD PLT'S DISCRETION TO FL280, IT WOULD HAVE HELPED IF THERE WAS A REMINDER TO CANCEL THE PLT DISCRETION TO FL280, BECAUSE OF ALL THE 2000 FT STEPDOWNS. SUPPLEMENTAL INFO FROM ACN 261525: ACR X (MD88) WAS ASSIGNED FL290 AND CONFLICTED WITH CPR Y (HS25) WHO WAS CONVERGING AT FL280. SUPPLEMENTAL INFO FROM ACN 261524: CPR Y WAS AT FL280. ACR X WAS CLRED TO FL290. ACR X BEGAN DSNDING OUT OF FL290. WHEN ACR X WAS APPROX FL285, CTLR ASKED ACR X HIS ASSIGNED ALT. ACR X SAID HE WAS CLRED PLT'S DISCRETION TO FL280. TAPE READBACK VERIFIED ACR X READ BACK FL290 ON INITIAL CLRNC, THUS A PLTDEV.

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.