Narrative:

We were on a short flight at 15000 ft. There was WX in the area and most flts were either deviating or on vectors around it. ATC was very busy. We were told to climb to maintain 'one seven thousand' ft and given an altimeter setting. I repeated the clearance back as the captain and I both heard it. My captain initiated a 1000 FPM climb using the autoplt. Shortly thereafter, ATC told us they were showing us in a climb (which we were). I then told the controller that she had cleared us to 17000 ft and that I had read it back. The controller told us that the clearance was not to 17000 ft but to maintain 'one seven zero' KTS. We slowed the aircraft and were then given a vector to resequence. At no time were we in conflict with other traffic, ie, no TA's or RA's from TCASII. If indeed we were told 170 KTS and not 17000 ft, then why the altimeter setting? That is something we are used to associating with a change in altitude or a handoff. Corrective action could be to preface a speed assignment using the word 'speed' as in 'reduce speed, maintain 170 KTS' and not just 'maintain 170 KTS.' it's very easy for these things to take place when things get busy. However, that is the reason for the readback. Listening is the key to communication.

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Original NASA ASRS Text

Title: SPD CLRNC IS UNDERSTOOD TO BE AN ALT CLRNC SO CLB WAS STARTED BY ACR.

Narrative: WE WERE ON A SHORT FLT AT 15000 FT. THERE WAS WX IN THE AREA AND MOST FLTS WERE EITHER DEVIATING OR ON VECTORS AROUND IT. ATC WAS VERY BUSY. WE WERE TOLD TO CLB TO MAINTAIN 'ONE SEVEN THOUSAND' FT AND GIVEN AN ALTIMETER SETTING. I REPEATED THE CLRNC BACK AS THE CAPT AND I BOTH HEARD IT. MY CAPT INITIATED A 1000 FPM CLB USING THE AUTOPLT. SHORTLY THEREAFTER, ATC TOLD US THEY WERE SHOWING US IN A CLB (WHICH WE WERE). I THEN TOLD THE CTLR THAT SHE HAD CLRED US TO 17000 FT AND THAT I HAD READ IT BACK. THE CTLR TOLD US THAT THE CLRNC WAS NOT TO 17000 FT BUT TO MAINTAIN 'ONE SEVEN ZERO' KTS. WE SLOWED THE ACFT AND WERE THEN GIVEN A VECTOR TO RESEQUENCE. AT NO TIME WERE WE IN CONFLICT WITH OTHER TFC, IE, NO TA'S OR RA'S FROM TCASII. IF INDEED WE WERE TOLD 170 KTS AND NOT 17000 FT, THEN WHY THE ALTIMETER SETTING? THAT IS SOMETHING WE ARE USED TO ASSOCIATING WITH A CHANGE IN ALT OR A HDOF. CORRECTIVE ACTION COULD BE TO PREFACE A SPD ASSIGNMENT USING THE WORD 'SPD' AS IN 'REDUCE SPD, MAINTAIN 170 KTS' AND NOT JUST 'MAINTAIN 170 KTS.' IT'S VERY EASY FOR THESE THINGS TO TAKE PLACE WHEN THINGS GET BUSY. HOWEVER, THAT IS THE REASON FOR THE READBACK. LISTENING IS THE KEY TO COM.

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.