Narrative:

Air carrier X level at FL180 was given clearance to FL210 to be at or above FL190 in 1 1/2 min. Air carrier X acknowledged, and complied. However, air carrier Y climbed to FL210. When I caught air carrier Y's climb through 17000 ft, I requested he stay at 17000 ft his assigned altitude. He replied he had FL210 in the box. I turned him right to a 090 degree heading and requested he descend to 17000 ft. Military Z at FL180 was then turned left to a 360 degree heading. I never heard air carrier Y acknowledge clearance. Air carrier X must have cut him out. In reviewing the tape, I did not hear air carrier Y acknowledge the clearance given to air carrier X. However, I heard air carrier X acknowledge and observed him climb to FL210. Air carrier Y was previously cleared to 17000 ft and was still climbing out of 13000 ft climbing to 17000 ft. There are 3 UHF and 3 VHF frequencys at pab sector. (125.55/398.9- 127.1/290.4-127.4/269.4). 1 pilot blocked the other out. These 6 frequencys are a definite problem at this sector. Supplemental information from acn 286552: I was acting as PNF and using the PA system to speak with our passenger. I was doing this as we were climbing through approximately 13000 ft. Upon resuming 'heads-up' active flight duties we were climbing through approximately 17000 ft. The captain advised me we had been told to expedite climb to FL210. As we climbed through approximately 17200 ft ATC questioned what altitude we were climbing to and I responded that we had been cleared to FL210. ZID said that our clearance was 17000 ft, told us to descend immediately to 17000 ft and turn right to 090 degree which we did. We had visual contact with another aircraft approximately 5 mi away, above us, and at our approximately 10-11 O'clock position. There did not seem to be a conflict. TCASII did not alert. The captain reiterated the clearance he had received (FL210) to ATC but we were told that our clearance was to 17000 ft. I do not know why the controller did not correct the captain when he read back the clearance to FL210. Oftentimes the controllers are extremely busy as are pilots. Sometimes frequencys are congested, call signs are similar, controllers don't acknowledge because 'they are on the other line' (pilots included) -- sometimes things are just very busy and there is a lot of 'stuff' going on. Supplemental information from acn 286952: 2ND aircraft turbo propeller military C26 IFR.

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Original NASA ASRS Text

Title: PLTDEV.

Narrative: ACR X LEVEL AT FL180 WAS GIVEN CLRNC TO FL210 TO BE AT OR ABOVE FL190 IN 1 1/2 MIN. ACR X ACKNOWLEDGED, AND COMPLIED. HOWEVER, ACR Y CLBED TO FL210. WHEN I CAUGHT ACR Y'S CLB THROUGH 17000 FT, I REQUESTED HE STAY AT 17000 FT HIS ASSIGNED ALT. HE REPLIED HE HAD FL210 IN THE BOX. I TURNED HIM R TO A 090 DEG HDG AND REQUESTED HE DSND TO 17000 FT. MIL Z AT FL180 WAS THEN TURNED L TO A 360 DEG HDG. I NEVER HEARD ACR Y ACKNOWLEDGE CLRNC. ACR X MUST HAVE CUT HIM OUT. IN REVIEWING THE TAPE, I DID NOT HEAR ACR Y ACKNOWLEDGE THE CLRNC GIVEN TO ACR X. HOWEVER, I HEARD ACR X ACKNOWLEDGE AND OBSERVED HIM CLB TO FL210. ACR Y WAS PREVIOUSLY CLRED TO 17000 FT AND WAS STILL CLBING OUT OF 13000 FT CLBING TO 17000 FT. THERE ARE 3 UHF AND 3 VHF FREQS AT PAB SECTOR. (125.55/398.9- 127.1/290.4-127.4/269.4). 1 PLT BLOCKED THE OTHER OUT. THESE 6 FREQS ARE A DEFINITE PROB AT THIS SECTOR. SUPPLEMENTAL INFO FROM ACN 286552: I WAS ACTING AS PNF AND USING THE PA SYS TO SPEAK WITH OUR PAX. I WAS DOING THIS AS WE WERE CLBING THROUGH APPROX 13000 FT. UPON RESUMING 'HEADS-UP' ACTIVE FLT DUTIES WE WERE CLBING THROUGH APPROX 17000 FT. THE CAPT ADVISED ME WE HAD BEEN TOLD TO EXPEDITE CLB TO FL210. AS WE CLBED THROUGH APPROX 17200 FT ATC QUESTIONED WHAT ALT WE WERE CLBING TO AND I RESPONDED THAT WE HAD BEEN CLRED TO FL210. ZID SAID THAT OUR CLRNC WAS 17000 FT, TOLD US TO DSND IMMEDIATELY TO 17000 FT AND TURN R TO 090 DEG WHICH WE DID. WE HAD VISUAL CONTACT WITH ANOTHER ACFT APPROX 5 MI AWAY, ABOVE US, AND AT OUR APPROX 10-11 O'CLOCK POS. THERE DID NOT SEEM TO BE A CONFLICT. TCASII DID NOT ALERT. THE CAPT REITERATED THE CLRNC HE HAD RECEIVED (FL210) TO ATC BUT WE WERE TOLD THAT OUR CLRNC WAS TO 17000 FT. I DO NOT KNOW WHY THE CTLR DID NOT CORRECT THE CAPT WHEN HE READ BACK THE CLRNC TO FL210. OFTENTIMES THE CTLRS ARE EXTREMELY BUSY AS ARE PLTS. SOMETIMES FREQS ARE CONGESTED, CALL SIGNS ARE SIMILAR, CTLRS DON'T ACKNOWLEDGE BECAUSE 'THEY ARE ON THE OTHER LINE' (PLTS INCLUDED) -- SOMETIMES THINGS ARE JUST VERY BUSY AND THERE IS A LOT OF 'STUFF' GOING ON. SUPPLEMENTAL INFO FROM ACN 286952: 2ND ACFT TURBO PROP MIL C26 IFR.

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.