Narrative:

While on a vector for spacing, ZID assigned our flight a speed of 250 KIAS for additional spacing. About 5 mins later, we were given a descent, cleared to the brickyard VOR (vhp), and then told 'if able do 300 KIAS.' near brickyard VOR the controller asked us our speed, at which time we said '250 KIAS.' the controller then replied, 'no. You were assigned 300 KIAS.' we then told the controller that our speed was '300 KIAS if able.' the controller, obviously confused and frustrated, made a few non pertinent remarks and then assigned us a speed of 290 KIAS. We believe that this event stems from the controller not remembering his initial clearance for us. By saying '300 KIAS if able,' the controller is leaving the speed to the flight crew's discretion. Also contributing to the controller's confusion was that there were several other aircraft in his sector, all going to the same destination, that were also on vectors and speed reductions for spacing. At the time, we had another pilot on our jump seat that agreed with our interpretation of the clearance. The jump seat rider made a comment about the controller's obviously overloaded situation well before there was any misunderstanding of airspeed assignments.

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Original NASA ASRS Text

Title: FLC OF A CANADAIR CL65 FAILED TO MAINTAIN AIRSPD GIVEN BY ARTCC CTLR DUE TO A MISUNDERSTANDING OVER THE 'IF ABLE' SPD.

Narrative: WHILE ON A VECTOR FOR SPACING, ZID ASSIGNED OUR FLT A SPD OF 250 KIAS FOR ADDITIONAL SPACING. ABOUT 5 MINS LATER, WE WERE GIVEN A DSCNT, CLRED TO THE BRICKYARD VOR (VHP), AND THEN TOLD 'IF ABLE DO 300 KIAS.' NEAR BRICKYARD VOR THE CTLR ASKED US OUR SPD, AT WHICH TIME WE SAID '250 KIAS.' THE CTLR THEN REPLIED, 'NO. YOU WERE ASSIGNED 300 KIAS.' WE THEN TOLD THE CTLR THAT OUR SPD WAS '300 KIAS IF ABLE.' THE CTLR, OBVIOUSLY CONFUSED AND FRUSTRATED, MADE A FEW NON PERTINENT REMARKS AND THEN ASSIGNED US A SPD OF 290 KIAS. WE BELIEVE THAT THIS EVENT STEMS FROM THE CTLR NOT REMEMBERING HIS INITIAL CLRNC FOR US. BY SAYING '300 KIAS IF ABLE,' THE CTLR IS LEAVING THE SPD TO THE FLC'S DISCRETION. ALSO CONTRIBUTING TO THE CTLR'S CONFUSION WAS THAT THERE WERE SEVERAL OTHER ACFT IN HIS SECTOR, ALL GOING TO THE SAME DEST, THAT WERE ALSO ON VECTORS AND SPD REDUCTIONS FOR SPACING. AT THE TIME, WE HAD ANOTHER PLT ON OUR JUMP SEAT THAT AGREED WITH OUR INTERP OF THE CLRNC. THE JUMP SEAT RIDER MADE A COMMENT ABOUT THE CTLR'S OBVIOUSLY OVERLOADED SIT WELL BEFORE THERE WAS ANY MISUNDERSTANDING OF AIRSPD ASSIGNMENTS.

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.