Narrative:

ZID had assigned us FL280 while we were climbing to a final cruise altitude of FL310. This altitude (FL280) was assigned shortly after initial contact with ZID. A few mins later, ZID changed our assigned altitude to FL270. We were in the mid teens at the time this assignment was made. Our rate of climb was approximately 1000 FPM, so 8-10 mins elapsed before we approached our assigned altitude of FL270. As we passed through FL268 ATC contacted us and informed us we had been assigned FL260. The first officer, as PNF, told ATC we had been assigned FL270. The controller denied assigning us FL270. As fp, while this exchanged occurred, I descended immediately to FL260. Less than 1 min after leveling at FL260, ATC cleared us to climb to FL310. We requested a contact phone number from ATC, and upon arrival at phx, I attempted to contact ZID quality assurance. The shift supervisor informed me that the mistake had been made by the controller, not us. This was based on his review of the tapes. My crew and I followed SOP regarding ATC communication and clearance which requires the PF to repeat the clearance back to the PNF after he has acknowledged it to ATC. I personally make it a practice to brief my crew that we will ask for clarification of any clearance if any member of the crew has doubts about what the clearance was, or did not hear it. I am not sure if there was conflicting traffic, as we do not have TCASII. I believe TCASII should be required on all transport category aircraft. If there were a conflict in this case TCASII might have prevented it. There was a great amount of traffic on frequency and I believe the controller was saturated.

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Original NASA ASRS Text

Title: LOSS OF SEPARATION WHEN CTR CTLR AMENDED RPTR'S DC8 CLB ALT TO FL270 INSTEAD OF FL260.

Narrative: ZID HAD ASSIGNED US FL280 WHILE WE WERE CLBING TO A FINAL CRUISE ALT OF FL310. THIS ALT (FL280) WAS ASSIGNED SHORTLY AFTER INITIAL CONTACT WITH ZID. A FEW MINS LATER, ZID CHANGED OUR ASSIGNED ALT TO FL270. WE WERE IN THE MID TEENS AT THE TIME THIS ASSIGNMENT WAS MADE. OUR RATE OF CLB WAS APPROX 1000 FPM, SO 8-10 MINS ELAPSED BEFORE WE APCHED OUR ASSIGNED ALT OF FL270. AS WE PASSED THROUGH FL268 ATC CONTACTED US AND INFORMED US WE HAD BEEN ASSIGNED FL260. THE FO, AS PNF, TOLD ATC WE HAD BEEN ASSIGNED FL270. THE CTLR DENIED ASSIGNING US FL270. AS FP, WHILE THIS EXCHANGED OCCURRED, I DSNDED IMMEDIATELY TO FL260. LESS THAN 1 MIN AFTER LEVELING AT FL260, ATC CLRED US TO CLB TO FL310. WE REQUESTED A CONTACT PHONE NUMBER FROM ATC, AND UPON ARRIVAL AT PHX, I ATTEMPTED TO CONTACT ZID QUALITY ASSURANCE. THE SHIFT SUPVR INFORMED ME THAT THE MISTAKE HAD BEEN MADE BY THE CTLR, NOT US. THIS WAS BASED ON HIS REVIEW OF THE TAPES. MY CREW AND I FOLLOWED SOP REGARDING ATC COM AND CLRNC WHICH REQUIRES THE PF TO REPEAT THE CLRNC BACK TO THE PNF AFTER HE HAS ACKNOWLEDGED IT TO ATC. I PERSONALLY MAKE IT A PRACTICE TO BRIEF MY CREW THAT WE WILL ASK FOR CLARIFICATION OF ANY CLRNC IF ANY MEMBER OF THE CREW HAS DOUBTS ABOUT WHAT THE CLRNC WAS, OR DID NOT HEAR IT. I AM NOT SURE IF THERE WAS CONFLICTING TFC, AS WE DO NOT HAVE TCASII. I BELIEVE TCASII SHOULD BE REQUIRED ON ALL TRANSPORT CATEGORY ACFT. IF THERE WERE A CONFLICT IN THIS CASE TCASII MIGHT HAVE PREVENTED IT. THERE WAS A GREAT AMOUNT OF TFC ON FREQ AND I BELIEVE THE CTLR WAS SATURATED.

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.