Narrative:

Flight from minneapolis to salt lake city, between rock springs (ocs) and ogden (ogd), the flight was cleared to descend at pd to FL240, then subsequently cleared to cross the 15 DME northeast of the ogd VORTAC at and maintain an assigned altitude. I understood the descent clearance to be to 'one-five thousand', as did the first officer. He set 15,000' in the altitude alerter, read back 'cross 15 NM northeast of ogd at and maintain one five thousand'. Descent was initiated from FL310 with that crossing restriction in mind. Descending thru approximately 16,000', the controller asked the altitude to which we were descending. When the first officer replied 'one-five thousand', the controller responded 'ok'. When queried about the clearance, he indicated that the minimum altitude to which the flight had been cleared was 'one-seven thousand', but that we were ok and he would coordinate. I am relatively certain that the center supervisor has checked the tape of the pertinent xmissions, but both the first officer and I remember hearing a crossing altitude of 15,000. I am certain that he read back 'one-five thousand'. The second officer was monitoring ramp frequency and was not aware of the clearance. It is possible to confuse a distance and altitude number when they are so close together. It might be considered good practice for the controller and the aircrew to say the altitude numbers twice when issuing and acknowledging clrncs like this.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT.

Narrative: FLT FROM MINNEAPOLIS TO SALT LAKE CITY, BTWN ROCK SPRINGS (OCS) AND OGDEN (OGD), THE FLT WAS CLRED TO DSND AT PD TO FL240, THEN SUBSEQUENTLY CLRED TO CROSS THE 15 DME NE OF THE OGD VORTAC AT AND MAINTAIN AN ASSIGNED ALT. I UNDERSTOOD THE DSCNT CLRNC TO BE TO 'ONE-FIVE THOUSAND', AS DID THE F/O. HE SET 15,000' IN THE ALT ALERTER, READ BACK 'CROSS 15 NM NE OF OGD AT AND MAINTAIN ONE FIVE THOUSAND'. DSCNT WAS INITIATED FROM FL310 WITH THAT XING RESTRICTION IN MIND. DSNDING THRU APPROX 16,000', THE CTLR ASKED THE ALT TO WHICH WE WERE DSNDING. WHEN THE F/O REPLIED 'ONE-FIVE THOUSAND', THE CTLR RESPONDED 'OK'. WHEN QUERIED ABOUT THE CLRNC, HE INDICATED THAT THE MINIMUM ALT TO WHICH THE FLT HAD BEEN CLRED WAS 'ONE-SEVEN THOUSAND', BUT THAT WE WERE OK AND HE WOULD COORDINATE. I AM RELATIVELY CERTAIN THAT THE CENTER SUPVR HAS CHECKED THE TAPE OF THE PERTINENT XMISSIONS, BUT BOTH THE F/O AND I REMEMBER HEARING A XING ALT OF 15,000. I AM CERTAIN THAT HE READ BACK 'ONE-FIVE THOUSAND'. THE S/O WAS MONITORING RAMP FREQ AND WAS NOT AWARE OF THE CLRNC. IT IS POSSIBLE TO CONFUSE A DISTANCE AND ALT NUMBER WHEN THEY ARE SO CLOSE TOGETHER. IT MIGHT BE CONSIDERED GOOD PRACTICE FOR THE CTLR AND THE AIRCREW TO SAY THE ALT NUMBERS TWICE WHEN ISSUING AND ACKNOWLEDGING CLRNCS LIKE THIS.

Data retrieved from NASA's ASRS site as of August 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.