Narrative:

At FL280, ZMP said 'air carrier X maintain two five zero for metering into msp.' first officer responded 'roger, descending to two five zero.' we descended to FL250. About 3 or 4 mins later, center asked 'what is your assigned altitude?' and we responded 'FL250.' he said 'no, that was your speed, slow to 250 and descend to FL240.' later we heard 2 other aircraft confused by instructions from same controller. He told one aircraft to 'maintain one seven zero for metering into msp.' they responded with question in tone, 'fly heading one seven zero?' and center responded, 'no, speed one seven zero.' fatigue on our part probably prevented us from questioning clearance, because I commented to first officer when starting down that it was a strange clearance. We had an 8 hour minimum rest layover the night before and early get-up last night.

Related reports:

Google
 

Original NASA ASRS Text

Title: ZMP CTLR CLRS ACR TO 'MAINTAIN TWO FIVE ZERO.' FLC INTERPS THIS AS A DSCNT CLRNC. CTLR WANTED SPD REDUCTION.

Narrative: AT FL280, ZMP SAID 'ACR X MAINTAIN TWO FIVE ZERO FOR METERING INTO MSP.' FO RESPONDED 'ROGER, DSNDING TO TWO FIVE ZERO.' WE DSNDED TO FL250. ABOUT 3 OR 4 MINS LATER, CTR ASKED 'WHAT IS YOUR ASSIGNED ALT?' AND WE RESPONDED 'FL250.' HE SAID 'NO, THAT WAS YOUR SPD, SLOW TO 250 AND DSND TO FL240.' LATER WE HEARD 2 OTHER ACFT CONFUSED BY INSTRUCTIONS FROM SAME CTLR. HE TOLD ONE ACFT TO 'MAINTAIN ONE SEVEN ZERO FOR METERING INTO MSP.' THEY RESPONDED WITH QUESTION IN TONE, 'FLY HDG ONE SEVEN ZERO?' AND CTR RESPONDED, 'NO, SPD ONE SEVEN ZERO.' FATIGUE ON OUR PART PROBABLY PREVENTED US FROM QUESTIONING CLRNC, BECAUSE I COMMENTED TO FO WHEN STARTING DOWN THAT IT WAS A STRANGE CLRNC. WE HAD AN 8 HR MINIMUM REST LAYOVER THE NIGHT BEFORE AND EARLY GET-UP LAST NIGHT.

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.