Narrative:

Air carrier X was at interim altitude of FL290 en route bws-srq. We received clearance to climb to FL330 and turned 10 degrees. We read back clearance and no acknowledgement after initiating climb received a 'TA' on our TCASII as we were climbing then fl 29.8. Sighted a MTR same direction 5 mi. 1 O'clock position descending. Questioned controller about traffic. He advised us that we should be at FL290 that we had received the wrong clearance we descended to 290 immediately topping out at FL30.2. There were similar call signs, and workload was extremely heavy, controller was doing a good job. Supplemental information from acn 201814. At approximately FL300 we received TCASII traffic alert at 1 O'clock 400 ft low. We visually observed military MTR crossing our nose low! We questioned controller about this traffic and were told to descend immediately back down to FL290. We read back our climb clearance to FL330 but did not receive another acknowledgement. Many aircraft on same frequency. Blocking numerous controller instructions which necessitated many read backs and confusion due to similar call signs.

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Original NASA ASRS Text

Title: ACR X UNAUTHORIZED CLB FROM ASSIGNED ALT RECEIVED TCASII TA HAD LTSS FROM MTR. PLTDEV.

Narrative: ACR X WAS AT INTERIM ALT OF FL290 ENRTE BWS-SRQ. WE RECEIVED CLRNC TO CLB TO FL330 AND TURNED 10 DEGS. WE READ BACK CLRNC AND NO ACKNOWLEDGEMENT AFTER INITIATING CLB RECEIVED A 'TA' ON OUR TCASII AS WE WERE CLBING THEN FL 29.8. SIGHTED A MTR SAME DIRECTION 5 MI. 1 O'CLOCK POS DSNDING. QUESTIONED CTLR ABOUT TFC. HE ADVISED US THAT WE SHOULD BE AT FL290 THAT WE HAD RECEIVED THE WRONG CLRNC WE DSNDED TO 290 IMMEDIATELY TOPPING OUT AT FL30.2. THERE WERE SIMILAR CALL SIGNS, AND WORKLOAD WAS EXTREMELY HVY, CTLR WAS DOING A GOOD JOB. SUPPLEMENTAL INFO FROM ACN 201814. AT APPROX FL300 WE RECEIVED TCASII TFC ALERT AT 1 O'CLOCK 400 FT LOW. WE VISUALLY OBSERVED MIL MTR XING OUR NOSE LOW! WE QUESTIONED CTLR ABOUT THIS TFC AND WERE TOLD TO DSND IMMEDIATELY BACK DOWN TO FL290. WE READ BACK OUR CLB CLRNC TO FL330 BUT DID NOT RECEIVE ANOTHER ACKNOWLEDGEMENT. MANY ACFT ON SAME FREQ. BLOCKING NUMEROUS CTLR INSTRUCTIONS WHICH NECESSITATED MANY READ BACKS AND CONFUSION DUE TO SIMILAR CALL SIGNS.

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.