Narrative:

The occurrence involved mdt aircraft overflying our sector at FL230 and an air carrier jet departure off cle climbing to FL220 on converging courses. After the air carrier had passed the other aircraft and they were diverging the air carrier's mode C readout showed FL225 and the controller asked the air carrier to verify at FL220. Air carrier replied, 'negative, climbing to FL230, that's what we were cleared to and that's what we read back.' the error occurred because, we the controllers, missed the altitude readback of the air carrier. Because the aircraft already diverged, evasive action was not necessary. The only way I can think of to reduce the chances of an error like this happening is to work on improving awareness to the pilot readbacks. Supplemental information from acn 104302: on climb out from cle, cleared djb 200 degrees to ape 017 degrees, blunt 2 cvg. Filed at FL220. First officer at controls of aircraft. Captain operating radios. ZOB gave climb clearance understood and read back by captain to FL230. Also noted verbally that we were cleared to FL230 and cabin altitude controller reset up 1000'. After level off at FL230, ZOB asked us to confirm that we were level at FL220. Responded, 'negative,' that we understood and read back our clearance to FL230 and were at FL230. Asked center for instructions. After some confusion, ZOB instructed us to descend to FL220. First officer descended aircraft and clarification of previous clearance was requested. ZOB was not forthcoming with information on whether clearance in error or not clearly annunciated. Instead we were given a frequency change to ind center. I have no question that clearance was understood and read back as FL230. No near miss or imminent conflict was involved. I do not, however, know if there was an airspace infringement with other aircraft as ZOB failed to respond to questions.

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Original NASA ASRS Text

Title: ACR-MLG CONFLICTED WITH AN MDT AT SAME ALT DUE TO ALT ASSIGNMENT HEARBACK PROBLEM.

Narrative: THE OCCURRENCE INVOLVED MDT ACFT OVERFLYING OUR SECTOR AT FL230 AND AN ACR JET DEP OFF CLE CLBING TO FL220 ON CONVERGING COURSES. AFTER THE ACR HAD PASSED THE OTHER ACFT AND THEY WERE DIVERGING THE ACR'S MODE C READOUT SHOWED FL225 AND THE CTLR ASKED THE ACR TO VERIFY AT FL220. ACR REPLIED, 'NEGATIVE, CLBING TO FL230, THAT'S WHAT WE WERE CLRED TO AND THAT'S WHAT WE READ BACK.' THE ERROR OCCURRED BECAUSE, WE THE CTLRS, MISSED THE ALT READBACK OF THE ACR. BECAUSE THE ACFT ALREADY DIVERGED, EVASIVE ACTION WAS NOT NECESSARY. THE ONLY WAY I CAN THINK OF TO REDUCE THE CHANCES OF AN ERROR LIKE THIS HAPPENING IS TO WORK ON IMPROVING AWARENESS TO THE PLT READBACKS. SUPPLEMENTAL INFO FROM ACN 104302: ON CLBOUT FROM CLE, CLRED DJB 200 DEGS TO APE 017 DEGS, BLUNT 2 CVG. FILED AT FL220. F/O AT CONTROLS OF ACFT. CAPT OPERATING RADIOS. ZOB GAVE CLB CLRNC UNDERSTOOD AND READ BACK BY CAPT TO FL230. ALSO NOTED VERBALLY THAT WE WERE CLRED TO FL230 AND CABIN ALT CTLR RESET UP 1000'. AFTER LEVEL OFF AT FL230, ZOB ASKED US TO CONFIRM THAT WE WERE LEVEL AT FL220. RESPONDED, 'NEGATIVE,' THAT WE UNDERSTOOD AND READ BACK OUR CLRNC TO FL230 AND WERE AT FL230. ASKED CENTER FOR INSTRUCTIONS. AFTER SOME CONFUSION, ZOB INSTRUCTED US TO DSND TO FL220. F/O DSNDED ACFT AND CLARIFICATION OF PREVIOUS CLRNC WAS REQUESTED. ZOB WAS NOT FORTHCOMING WITH INFO ON WHETHER CLRNC IN ERROR OR NOT CLEARLY ANNUNCIATED. INSTEAD WE WERE GIVEN A FREQ CHANGE TO IND CENTER. I HAVE NO QUESTION THAT CLRNC WAS UNDERSTOOD AND READ BACK AS FL230. NO NEAR MISS OR IMMINENT CONFLICT WAS INVOLVED. I DO NOT, HOWEVER, KNOW IF THERE WAS AN AIRSPACE INFRINGEMENT WITH OTHER ACFT AS ZOB FAILED TO RESPOND TO QUESTIONS.

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.